News & Events



February 2, 2024:

THEMIS researchers use citizen science video to study new features (continued from front page):

Citizen scientist photo of STEVE, providing researchers with unprecedented detail of its fine structure. The image was selected as the cover of the Journal of Geophysics Research. Credit: Alan Dyer.

A recent article published in Science News details the captivating yet mysterious phenomenon known as STEVE (Strong Thermal Emission Velocity Enhancement), a rare sky glow observed by citizen scientists like Alan Dyer in rural Alberta, Canada. Unlike traditional auroras, STEVE appears as a ribbon of mauve closer to the equator and exhibits unique characteristics. Dyer's high-resolution footage of STEVE provided scientists, particularly THEMIS researcher Toshi Nishimura from Boston University, with unprecedented details. The video revealed a flickering torrent of purplish-white fuzz that challenged existing understandings of atmospheric chemistry.

Scientists have been grappling with the enigmatic nature of STEVE since its introduction to the scientific community in 2016. While initially thought to be related to auroras, STEVE's distinct purple hue and different behavior have raised numerous questions about its origins and underlying mechanisms. Recent observations suggest a connection between STEVE and another atmospheric phenomenon called stable auroral red (SAR) arcs, indicating a complex interplay of factors contributing to STEVE's appearance.

Further complicating the understanding of STEVE is the discovery of its association with green stripes known as the "picket fence," which was initially mistaken for a type of aurora. However, detailed analysis suggests that the picket fence's green glow may stem from different processes than traditional auroras, possibly involving atmospheric electric fields. Computer modeling and proposed rocket missions aim to shed light on these phenomena and confirm the existence of such electric fields.

NASA's upcoming missions, including the Geospace Dynamics Constellation mission, hold promise for gathering more data to elucidate the mysteries surrounding STEVE and related atmospheric phenomena. Despite the challenges, citizen scientists like Dyer remain instrumental in capturing observations of STEVE from the ground, contributing valuable data that continue to puzzle and intrigue researchers in the field of space physics.

Temming, M. (2023), STEVE and other aurora-like glows perplex scientists with their complex physics, Science News, Published December 2023.

Citation: Nishimura, Y., Dyer, A., Donovan, E. F., Angelopoulos, V. (2023). Fine-scale structures of STEVE revealed by 4K imaging. Journal of Geophysical Research: Space Physics, 128, e2023JA032008.

September 3, 2023:

THEMIS observations of magnetopause Rayleigh-Taylor instability selected as JGR cover:

Artist rendition of the Rayleigh-Taylor Instability at Earth's Magnetopause, when the solar wind dynamic pressure suddenly drops. Credit: G.Q. Yan

Congratulations to Guang Qing Yan et al., for their recent paper on the detailed microphysics of the Rayleigh-Taylor instability in the magnetopause using THEMIS, selected as the cover art for the latest issue of Journal of Geophysics Research, Space Physics.

The magnetopause, the outermost edge that our planet's intrinsic magnetic field reaches, is always in motion. The macroscopic acceleration at the magnetopause is sometimes as large as a few km/s2. Theoretically, such an acceleration of the boundary can facilitate an instability in the motion of the interface, the R-T instability. Such an instability can, in turn, cause a transfer of plasma across the magnetopause, from solar wind into near-Earth space. If the resulting particles are sufficiently energetic, operations of many satellites in space can be threatened. However, details of how the instability operates at the magnetopause have been neither verified nor observed in spacecraft observations. Recent measurements from NASA's THEMIS mission indicate that the R-T instability can be excited at the magnetopause, and many details of the instability, including those of its electric field and plasma transport across the magnetopause, appear to be verified in those observations.

For more detail please read the THEMIS nugget summary here or the paper linked below.

Yan, G. Q., Parks, G. K., Mozer, F. S., Goldstein, M. L., Chen, T., & Liu, Y. (2023). Rayleigh-Taylor instability observed at the dayside magnetopause under northward interplanetary magnetic field. Journal of Geophysical Research: Space Physics, 128, e2023JA031461.

May 15, 2023:

Kelvin-Helmholtz waves shown to influence equinox geomagnetic activity:

Congratulations to Shiva Kavosi et al., for their recent paper on KH-waves and their influence on equinoctial geomagnetic activity, selected as an Editor's Highlight in Nature Communications. Using THEMIS observations across more than a solar cycle was key to the discovery.

More accurate space-weather predictions and safer satellite navigation through radiation belts could someday result from new insights into “space waves,” researchers at Embry-Riddle Aeronautical University reported. The group’s latest research, published on May 4, 2023, by the journal Nature Communications, shows that seasonal and daily variations in the Earth’s magnetic tilt, toward or away from the Sun, can trigger changes in large-wavelength space waves.

The simulation (right) shows the Earth’s magnetic environment during the equinox and the solstice. As the solar wind – a flow of particles from the Sun – hits the Earth’s magnetic environment, it can create breaking waves known as Kelvin-Helmholtz waves. This occurs more often during the equinoxes due to the orientation of the Sun’s and Earth’s magnetic fields (left). Credits: Shiva Kavosi, ERAU

These breaking waves, known as Kelvin-Helmholtz waves, occur at the boundary between the solar wind and the Earth’s magnetic shield. The waves happen much more frequently around the spring and fall seasons, researchers reported, while wave activity is poor around summer and winter. As plasma or solar wind streams from the Sun at speeds up to 1 million miles per hour, it pushes energy, mass and momentum toward the planet’s magnetic shield. It also whips up space waves. Fast-moving solar wind can’t pass directly through the Earth’s magnetic shield, so it thunders along the magnetosphere, propelling Kelvin-Helmholtz waves with massive peaks up to 15,000 kilometers (km) high and 40,000 km long.

Astronaut Safety and Satellite Communication

“Through these waves, solar wind plasma particles can propagate into the magnetosphere, leading to variations in radiation belt fluxes of energetic particles—regions of dangerous radiation—that may affect astronaut safety and satellite communications,” said Dr. Shiva Kavosi, a research associate at Embry-Riddle and first author of the “Nature Communications” paper. “On the ground, these events can impact power grids and Global Positioning Systems.” Describing the properties of space waves and the mechanisms that cause them to intensify is key to understanding and forecasting space weather, Kavosi noted: “Space weather events represent an increasing threat, yet in many cases, we don’t understand exactly what controls it. Any progress we can make in understanding the mechanisms behind space weather disturbances will improve our ability to provide forecasts and warnings.”

In trying to understand the causes of seasonal and diurnal variations of geomagnetic activity, researchers in the field have set forth several different hypotheses. For example, the Russell-McPherron (R-M) effect, first described in 1973, explains why auroras are more frequent and brighter in the spring and fall, based on the interplay of the Earth’s dipole tilt and a small magnetic field near the Sun’s equator. “We don’t have all the answers yet,” said Dr. Katariina Nykyri, professor of physics and associate director for the Center of Space and Atmospheric Research at Embry-Riddle, “but our paper shows that the R-M effect is not the only explanation for the seasonal variation of geomagnetic activities. Equinox-driven events, based on the Earth’s dipole tilt, and R-M effects could operate simultaneously.”

In the future, Nykyri added, constellations of spacecraft in the solar wind and magnetosphere could more fully explain the complicated, multi-scale physics of space weather phenomena. “Such a system would allow advanced warnings of space weather to inform the operators of rocket launches and electrical power grids,” she said. The “Nature Communications” paper concludes that “KH waves activity exhibit seasonal and diurnal variations, indicating the critical role of dipole tilt in modulating KHI across the magnetopause as a function of time.”

Anon. (2023), `Space waves' offer new clues to space weather, Embry Riddle Newsroom, Published on May 4, 2023.

Johnson-Groh, M. (2023), NASA Spacecraft Reveal How Earth’s Tilt Causes Seasons in Space Weather, NASA Sun Spot, Published on May 15, 2023.

Kavosi, S., Raeder, J., Johnson, J.R., Nykyri, K., Farrugia, C.J. (2023) Seasonal and diurnal variations of Kelvin-Helmholtz Instability at terrestrial magnetopause. Nat Commun 14, 2513.

April 17, 2023:

Listen to THEMIS data using HARP Citizen Science web app:

Congratulations to Mike Hartinger et al., for the launch of their new NASA Citizen Science web app called HARP, highlighted in Washington Post and NPR.

An international team of researchers invites the public to help in the search for space weather signals: magnetic vibrations around Earth called plasma waves. This new project, Heliophysics Audified: Resonances in Plasmas, or HARP, has just released a web app that takes THEMIS satellite magnetic data and converts it into sounds that the public can listen to and classify.

Learn about the HARP project, where you can help researchers identify plasma waves and improve their models of space weather. Credit: HARP Team, NASA, NCSA-AVL-UIUC, U. Calgary

Plasma waves arise when charged particles from the sun impact Earth's magnetic field, causing it to vibrate or resonate, unleashing radiation that can potentially damage spacecraft. On the brighter side, plasma waves can also generate the beautiful northern and southern lights. Results from the HARP analysis can be fed into space weather models to improve predictions and help clarify the mysterious processes that govern the auroras.

Plasma waves in Earth's environment are invisible, but they can influence the formation of the aurora. Pulsating and shimmering regions appear when charged particles impact Earth's upper atmosphere, making it glow. Credit: Auroral Imaging Group, U. Calgary

"Earth's magnetic field and plasma waves are invisible to cameras," said Mike Hartinger, principal investigator at SSI and a researcher in the UCLA Department of Earth, Planetary, and Space Sciences (EPSS). "HARP uses data collected by NASA's THEMIS satellites traveling through the changing magnetic environment around our planet, where plasma waves can form."

Just as seismologists use earthquake vibrations to "see" inside the Earth, HARP uses magnetic vibrations to investigate how space weather evolves around our planet in response to the Sun's activity.

Plasmas are charged particles that emanate from the sun, which blows a solar wind in continuous streams and explosive eruptions. When the solar wind impacts Earth's magnetic field, different types of plasma waves can form, analogous to vibrations formed by different musical instruments. Credit: Q.-G. Zong, Peking Univ.; M. O. Archer, Imperial College London; M. Hartinger, SSI, UCLA EPSS

HARP expands upon a pilot project in the UK led by team member Martin Archer of Imperial College London, in which high school students found a new complex pattern of plasma waves and became co-authors in a peer-reviewed journal publication. Studies show that people's eyes and ears in combination are better at finding hidden wave patterns than using computer algorithms or eyes alone. Anyone can work with NASA satellite data with just a few minutes of training and make an important contribution to space science.

"We need the public's help to identify plasma waves in huge datasets gathered over the past 16 years by NASA's THEMIS satellites," said Hartinger.

An overview of the HARP graphic interface and sample sound event from 2012. Credit: HARP Team, Martin Archer, Imperial College London

HARP users will be greeted with a brief tutorial, where they listen to the satellite data simultaneously while viewing it in a graph of frequency and intensity vs. time, called a spectrogram. Users can draw boxes around interesting features and describe their characteristics, such as changes in pitch or whether there are single or multiple tones, and jot down any other observations.

Although HARP currently uses only one satellite mission, the next step is to add other heliophysics satellites and data sources to incorporate more types of plasma waves throughout the solar system. The public holds the key to the success of HARP and can hasten future discoveries, visit and sign up today!

Archer, M.O., Nykyri, K. (2023), Listen to the Sounds of Space, ISSI Bern, Published on April 17, 2023.

Baker, H. (2023), Eerie sounds triggered by plasma waves hitting Earth's magnetic field captured in new NASA sound clip, Livescience, Published on April 18, 2023.

Blakemore, E., (2023), Want to listen to space noise? NASA wants to hear from you, Washington Post, Published on Apr. 23, 2023.

Hoeflinger, J. (2023), Imperial researchers team up with NASA to launch new citizen science study, Imperial College London, Published on April 17, 2023.

Kwong, E., Barber, R.G. (2023), From 'Short Wave': magnetosphere music, Jupiter's icy moons and a runaway black hole, aired on NPR All Things Considered on April 20, 2023.

Masongsong, E. (2023), UCLA Scientists Inviting People to Explore Space With Their Ears, UCLA EPSS website, Published on April 19, 2023.

Matthew, Z. (2023), NASA and UCLA want you to help identify the sounds of space, KCRW Greater LA Podcast, Published on May 4, 2023.

Thomas, V. (2023), Help Discover the Sounds of Space Played by NASA’s HARP, NASA website, Published on April 17, 2023.

April 1, 2023:

THEMIS researcher talks about STEVE in Washington Post:

Congratulations to Toshi Nishimura et al. for receiving quotes and a reference to their Frontiers paper using THEMIS data, featured in a recent article on STEVE in the Washington Post.

STEVE is not an aurora, but you can think of it as a shy, distant cousin. It looks as if it could be part of the family, but it has its own distinct style. The phenomenon generally appears as a long, slender purple-and-white arc, sometimes accompanied by a structure that looks like a green picket fence. It is fainter and narrower, and occurs at lower latitudes than most auroras. It is also harder to predict.

What are some impacts of STEVE? Even if you haven’t seen the awe-inspiring STEVE, its impacts could be experienced by Earthlings in other ways.

STEVE researcher Toshi Nishimura recounted at least one instance in which a radio signal from a radar network disappeared for 30 minutes as STEVE appeared, but then returned once the ghostly light left the area, suggesting that the phenomenon can disrupt such signals. Similar blackouts can occur with space weather associated with auroras, but he said STEVE occurs in a different region. He said it "would have a larger impact on densely populated regions at lower latitudes than aurora.”

STEVE is important because Earth’s magnetic field “is doing something different from usual. … We still don’t understand why,” said Nishimura, who recently published a study on the mysteries of STEVE. He has yet to see the phenomenon in person.

A photo of STEVE captured in Plumas in August 2022. STEVE is often accompanied by a green picket fence structure, appearing here at the lower edge of the pink arc. (Donna Lach)

Nishimura, a researcher at Boston University, said STEVE seems to always occur during local and brief disturbances in Earth’s magnetic field, called substorms. Substorms can occur without a large geomagnetic storm and happen daily. Yet despite the ubiquity of substorms, researchers are perplexed about why STEVE sightings are still relatively rare compared with auroras.

With every photo and report, people are understanding more about this relatively unexplored part of our atmosphere, and its connection with the sun.

Patel, K., (2023), How to find STEVE, the purple streak that looks like an aurora but isn’t, Washington Post, Published on Apr. 1, 2023.
Citation: Nishimura, Y. et al. (2023), Unsolved problems in Strong Thermal Emission Velocity Enhancement (STEVE) and the picket fence, Front. Astron. Space Sci., 10,

February 1, 2023:

THEMIS data reveals lunar tide in the plasmasphere:

Congrats to Xiao et al. for their discovery of a lunar tide effect on the Earth's plasmapause. For their paper published in the journal Nature Physics, the group used data from multiple spacecraft including THEMIS-ARTEMIS and Van Allen Probes over a nearly 40-year period to measure tidal perturbations in the plasmapause.

Early scientists found a connection between the tides and the movement of the moon thousands of years ago. More recent evidence suggests the moon's pull acts on the ionosphere as well. In this new study, the researchers wondered if the moon might also have an impact on the plasmasphere. The plasmasphere is a toroidal mass of plasma that surrounds the Earth. It lies beyond the ionosphere and is made up mostly of electrons and protons. Its particles are charged by the ionosphere, and its outer boundary is known as the plasmapause. To find out if it is impacted by the moon's gravity, the researchers obtained data from approximately 36,000 crossings of the plasmasphere by spacecraft over the years 1977 to 2015. They also used data from the Van Allen Probes from the years 2012 to 2019 to gain a better perspective on possible plasmasphere modulations.

Ocean tides (blue) compared to plasmapause tides (orange). Credit: Q.Q. Shi, Shandong University (video link)

The group found that they were able to isolate tidal variations in the shape of the plasmapause that could be associated with the position of the moon, clear evidence that the moon does exert an influence on the plasmasphere. They also found that they were able to see monthly periodicities in the changes in plasmapause. The researchers propose that three basic elements are responsible for the tidal variations: the existence of a two-body system—namely the Earth and moon—along with the existence of the plasma field and the existence of the magnetic field. They further suggest that similar tidal variations likely occur in other two-body systems throughout the universe.

Yirka, B., (2023), Evidence found of tidal impact on the plasmasphere,, Published on Feb. 1, 2023.

Xiao, C. et al. (2023), Moon can cause a tide in Earth’s “plasma ocean," Nature Portfolio Astronomy Community, Published Jan. 27, 2023.

Phillips, T. (2023), Strange tides in the plasmasphere,, Published on Feb. 8, 2023.

Hua, X. (2023), Scientists find evidence of lunar tide impact on plasmasphere, China Daily, Published Feb. 7, 2023.

Luntz, S. (2023), Even The Earth’s Magnetic Field Has Moon-Driven Tides, IFL Science, Published Feb. 6, 2023.

Stan, J. (2023), Moon Exerts Obscure Tidal Force 'Plasma Ocean' That Creates Fluctuation on Earth's Magnetosphere, Study Reveals, Science Times, Published Feb. 3, 2023.

Citation: Xiao, C. et al. (2023), Evidence for lunar tide effects in Earth's plasmasphere, Nature Physics. DOI: 10.1038/s41567-022-01882-8

October 7, 2022:

Space Raindrops Splashing on Earth’s Magnetic Umbrella :

Congrats to Vuorinen et al. for their recent feature article in Eos magazine, profiling THEMIS-ARTEMIS measurements of magnetosheath jets and their influence on magnetic reconnection.

Though not as damaging as extreme space weather events, showers of plasma jets hit Earth’s magnetic shield every day—yet we’re only beginning to understand their effects. Every few minutes, Earth-sized “droplets” of plasma rain down from space toward Earth. Instead of crashing catastrophically to the ground, these droplet/s, called magnetosheath jets, hit and are deflected by the outer reaches of Earth’s magnetic field.

Despite their frequent occurrence near Earth and likely ubiquity across the solar system, the study of magnetosheath jets is young, and there is much we do not know about their origins and behavior. Specifically, their potential effects on space weather—the phenomena we experience on Earth due to the ever-changing stream of plasma that flows through our solar system—are unclear and still being investigated. Therefore, these jets are not currently factored into space weather models or predictions. Here we discuss recent findings in this field and important questions that remain to be answered.

Fig. 1. The solar wind with its interplanetary magnetic field (yellow lines) flows from the Sun and forms a shock wave called the bow shock (bright orange line) where it meets Earth’s magnetic field upstream of the planet. At the bow shock, the solar wind is slowed, except for fast plasma jets (orange globules) emerging from where the shock wave is corrugated, adjacent to the turbulent foreshock region (brown shading at top right). Jets travel through the magnetosheath (red swirls), and eventually, some of them impact the magnetopause (bright blue line), the outer edge of Earth’s magnetosphere (blue shading). Earth’s magnetic field (faint blue lines) and an aurora in Earth’s ionosphere are also represented. Credit: E. Masongsong, H. Hietala, L. Vuorinen, A. LaMoury

Our knowledge of magnetosheath jets relies on data captured by spacecraft surveying the near-Earth electromagnetic environment. Launched in 2007 and still going strong, NASA’s THEMIS-ARTEMIS five-satellite mission in particular has greatly enhanced our understanding of many areas of space and space weather, from the solar wind and its interactions with Earth’s magnetic field to the aurora and even plasmas around the Moon.

In a recent study using THEMIS data, researchers observed that the frequency of jets reaching the magnetopause is highly dependent on the properties of the solar wind at the bow shock [LaMoury et al., 2021]. They found that when the solar wind’s magnetic field is nearly radial, jets are expected to hit the magnetopause every few minutes—that is, over 17 times more often than when the solar wind’s magnetic field reaches Earth at an oblique angle. They also found that more jets arose during intervals of “fast” solar wind (which travels about twice the normal velocity). These intervals vary with the 11-year solar cycle, so the number of jets hitting the magnetopause may exhibit the same periodic dependence.

In addition to controlling the structure of different bow shock regions, the orientation of the solar wind magnetic field influences what happens at the magnetopause. Zooming in on this boundary where the solar wind magnetic field meets Earth’s magnetic field, we see that geometry comes into play once again.

Namely, if the solar wind magnetic field is oriented southward, opposite to Earth’s northward magnetic field, erosion of the magnetopause can occur via a process known as magnetic reconnection (Figure 2). Reconnection is a key process in plasma physics, in which the connectedness of magnetic field lines is fundamentally changed and energy stored in the magnetic field is explosively released.

In the case of the magnetopause, antiparallel field lines of the solar wind connect with those of Earth, peeling them away from the Sun-facing side of the magnetosphere. This has the effect of weakening Earth’s magnetic shield, allowing solar wind plasma and energy to enter Earth’s magnetosphere. Thus, one of the most critical aspects of forecasting space weather is monitoring the solar wind magnetic field orientation far upstream of Earth.

Fig. 2. Antiparallel magnetic field lines can merge during magnetic reconnection, which transforms magnetic energy into the kinetic energy of particles. At Earth’s magnetopause (bright blue), this can happen when Earth’s northward-oriented (☉) magnetic field (gray curve with conical arrows) meets a plasma jet (orange globule) with southward-oriented (⊗) magnetic field. Credit: E. Masongsong, H. Hietala, L. Vuorinen, A. LaMoury, F. Beyene

Although measuring the north–south component of the solar wind magnetic field before it arrives to Earth (together with solar wind speed and density) can help us prepare for space weather storms, it does not give us the full picture of how space weather evolves at Earth. Much more frequent rain showers (i.e., jets) may play a role that, until recently, had not been considered to control magnetic reconnection, sparking debate in the magnetospheric physics community. Jets, because of their high dynamic pressure, have been observed compressing the magnetopause boundary to help initiate reconnection, as opposite magnetic fields are being pushed together more efficiently [Hietala et al., 2018].

In addition, researchers have suggested that the magnetic field orientation in jets may be different from field orientations in the surrounding magnetosheath. Nykyri et al. [2019] observed jets with southward magnetic fields propagating toward the magnetopause and triggering reconnection despite measurements at the time showing the solar wind magnetic field was oriented northward. This was likely not an isolated occurrence, and it caused a chain of events leading to increased geomagnetic activity on the nightside of the magnetosphere, opposite from the Sun.

Vuorinen et al. [2021] performed a statistical study of the north–south component in jets versus the surrounding magnetosheath using THEMIS data, further confirming that jets often carry southward magnetic fields even when the solar wind magnetic field is northward. The combination of jets compressing and introducing southward fields to the magnetopause may be favorable for triggering reconnection, even during solar wind conditions when we are not typically expecting it. This result highlights the importance of studying the magnetosphere’s behavior during times of a radial interplanetary magnetic field.

Vuorinen, L., A. LaMoury, E. Masongsong, and H. Hietala (2022), Space raindrops splashing on Earth’s magnetic umbrella, Eos, 103, Published on 7 October 2022..

Citation: Hietala, H., et al. (2018), In situ observations of a magnetosheath high-speed jet triggering magnetopause reconnection, Geophys. Res. Lett., 45, 1,732–1,740,

LaMoury, A. T., et al. (2021), Solar wind control of magnetosheath jet formation and propagation to the magnetopause, J. Geophys. Res. Space Phys., 126, e2021JA029592,

Nykyri, K., et al. (2019), Can enhanced flux loading by high-speed jets lead to a substorm? Multipoint detection of the Christmas Day substorm onset at 08:17 UT, 2015, J. Geophys. Res. Space Phys., 124, 4,314–4,340,

Plaschke, F., et al. (2018), Jets downstream of collisionless shocks, Space Sci. Rev., 214, 81,

Raptis, S., et al. (2022), Downstream high-speed plasma jet generation as a direct consequence of shock reformation, Nat. Commun., 13, 598,

Vuorinen, L., et al. (2021), Magnetic field in magnetosheath jets: A statistical study of Bz near the magnetopause, J. Geophys. Res. Space Phys., 126, e2021JA029188,

June 2, 2022:

CLUSTER-THEMIS-MMS observations contribute to big picture of auroral beads :

Congrats to Petrinec et al. for their recent publication profiling magnetopause vortices and auroral bead formation with 13 spacecraft, including THEMIS, CLUSTER, MMS, Geotail and DMSP.

One solar stormy day in November 2018, 13 spacecraft including ESA’s Cluster mission were in the right place at the right time to spot a process that has never been seen in its entirety before. Their observations explain how vortices at the edge of Earth’s magnetosphere can cause auroral beads to dot the sky a hundred thousand kilometres below.

This connection between auroral beads appearing on Earth’s ‘dayside’ (or Sun-facing side) and the vortices confirms a theory about how these unique auroras – known as beads because they look like a string of pearls hung across the sky – form. As some spacecraft observed the vortices themselves, others saw that a stream of charged particles used the vortices as access points to tunnel down towards Earth’s surface, causing the sky to glow.

Using multi-spacecraft observations, researchers explain how vortices at the edge of Earth’s magnetosphere can cause auroral beads to dot the sky a hundred thousand kilometres below: 1) The solar wind 'blows' across the magnetopause, rolling it up into giant whirlpool-like vortices. 2) Electrons enter the magnetosphere through the vortices and travel down towards the upper atmosphere. 3) In the upper atmosphere, electrons collide with hydrogen, oxygen and nitrogen, causing auroral beads to glow in the sky.

On 6 November 2018, 12 spacecraft were all located close to the magnetopause – the thin boundary at the outer edge of the magnetosphere – on the night side of Earth, where the magnetosphere stretches out into a tail.

Among the 12 spacecraft located close to the magnetosphere were the four that make up ESA’s Cluster mission, as well as NASA’s four Magnetospheric Multiscale (MMS) spacecraft and three Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft, and JAXA’s Geotail. In addition, a US Defence Meteorological Satellite Program (DMSP) satellite observed the auroral beads from close to Earth’s surface.

“This discovery shows that the Cluster spacecraft are part of a ‘magnetospheric orchestra’ of missions that together enable extra science that is not possible to achieve with each mission individually,” explains Philippe Escoubet, ESA’s Cluster project scientist.

The vortices – which themselves were originally detected by Cluster – are formed when the solar wind blows past the magnetopause. Just as wind on Earth can whip up oceans and clouds, the solar wind can roll up the magnetopause into giant waves comprised of whirlpool-like vortices.

When a vortex is at the ‘goldilocks’ size – not too big, but not too small – electrons from the solar wind swirl around its centre, before entering the magnetosphere, travelling towards and reaching Earth’s upper atmosphere. There, the electrons collide with hydrogen, oxygen and nitrogen, causing them to glow and form an auroral bead in the sky. These round beads – one for each vortex – appear in groups that follow each other across the sky. This is in contrast to ‘normal’ aurora which are flatter, more elongated and not so well organised.

Philippe continues: “Cluster has been operating for almost 22 years now. In the beginning, it was one of the only missions observing the magnetosphere, so we were mainly comparing the four spacecraft with each other. But nowadays we can compare their data with those from other missions, such as MMS and THEMIS.”

This research demonstrates the importance of multiple different spacecraft, each with their own complement of scientific instruments, monitoring the same events from different vantage points.

ESA, Magnetic vortices explain mysterious auroral beads, June 2, 2022.

Citation: Petrinec, S. et al. (2022), Multi-Spacecraft Observations of Fluctuations Occurring Along the Dusk Flank Magnetopause, and Testing the Connection to an Observed Ionospheric Bead, Frontiers in Astronomy and Space Sciences. DOI: 10.3389/fspas.2022.827612

March 29, 2022:

THEMIS-ELFIN observations of whistler wave electron precipitation:

Congrats to Zhang et al. for their recent publication in Nature Communications. Using THEMIS along with ELFIN CubeSat low-altitude electron measurements, they confirmed that oblique whistler waves can energize electrons to >100keV and fill the loss cone beyond predictions by current models.

UCLA scientists have discovered a new source of super-fast, energetic electrons raining down on Earth’s atmosphere, a phenomenon that contributes to the colorful aurora borealis but also poses hazards to satellites, spacecraft and astronauts.

The researchers observed unexpected, rapid “electron precipitation” from low-Earth orbit using the ELFIN mission, a pair of tiny satellites built and operated on the UCLA campus by undergraduate and graduate students guided by a small team of staff mentors.

By combining the ELFIN data with more distant observations from NASA’s THEMIS spacecraft, the scientists determined that the sudden downpour was caused by whistler waves, a type of electromagnetic wave that ripples through plasma in space and affects electrons in the Earth’s magnetosphere, causing them to “spill over” into the atmosphere.

The THEMIS and ELFIN satellites (orbits shown in cyan and green, respectively) worked together to help understand the mystery of electron rain. When whistler waves (purple) interact with the electrons, they can give them extra energy (red spiral), which causes them to fall into the atmosphere.

Their findings, published March 25 in the journal Nature Communications, demonstrate that whistler waves are responsible for far more electron rain than current theories and space weather models predict.

“ELFIN is the first satellite to measure these super-fast electrons,” said Xiaojia Zhang, lead author and a researcher in UCLA’s department of Earth, planetary and space sciences. “The mission is yielding new insights due to its unique vantage point in the chain of events that produces them.”

Central to that chain of events is the near-Earth space environment, which is filled with charged particles orbiting in giant rings around the planet, called Van Allen radiation belts. Electrons in these belts travel in Slinky-like spirals that literally bounce between the Earth’s north and south poles. Under certain conditions, whistler waves are generated within the radiation belts, energizing and speeding up the electrons. This effectively stretches out the electrons’ travel path so much that they fall out of the belts and precipitate into the atmosphere, creating the electron rain.

One can imagine the Van Allen belts as a large reservoir filled with water — or, in this case, electrons. As the reservoir fills, water periodically spirals down into a relief drain to keep the basin from overflowing. But when large waves occur in the reservoir, the sloshing water spills over the edge, faster and in greater volume than the relief drainage. ELFIN, which is downstream of both flows, is able to properly measure the contributions from each flow.

The low-altitude electron rain measurements by ELFIN, combined with the THEMIS observations of whistler waves in space and sophisticated computer modeling, allowed the team to understand in detail the process by which the waves cause rapid torrents of electrons to flow into the atmosphere.

The findings are particularly important because current theories and space weather models, while accounting for other sources of electrons entering the atmosphere, do not predict this extra whistler wave–induced electron flow, which can affect Earth’s atmospheric chemistry, pose risks to spacecraft and damage low-orbiting satellites.

The researchers further showed that this type of radiation belt electron loss to the atmosphere can increase significantly during geomagnetic storms, disturbances caused by enhanced solar activity that can affect near-Earth space and Earth’s magnetic environment.

Although space is commonly thought to be separate from our upper atmosphere, the two are inextricably linked. Understanding how they’re linked can benefit satellites and astronauts passing through the region, which are increasingly important for commerce, telecommunications and space tourism.

Since its inception in 2013, more than 300 UCLA students have worked on ELFIN (Electron Losses and Fields investigation), which is funded by NASA and the National Science Foundation. The two microsatellites, each about the size of a loaf of bread and weighing roughly 8 pounds, were launched into orbit in 2018, and since then have been observing the activity of energetic electrons and helping scientists to better understand the effect of magnetic storms in near-Earth space. The satellites are operated from the UCLA Mission Operations Center on campus.

“It’s so rewarding to have increased our knowledge of space science using data from the hardware we built ourselves,” said Colin Wilkins, a co-author of the current research who is the instrument lead on ELFIN and a space physics doctoral student in the department of Earth, planetary and space sciences.

Masongsong, E. (2022), UCLA researchers discover source of super-fast ‘electron rain.' UCLA Newsroom, March 29, 2022.

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Citation: Zhang, X.-J., Artemyev, A. V., Angelopoulos, V., Tsai, E., Wilkins, C., Kasahara, S., Mourenas, D., Yokota, S., Keika, K., Hori, T., Miyoshi, Y., Shinohara, I., Matsuoka, A. (2022), Superfast precipitation of energetic electrons in the radiation belts of the Earth, Nat. Comm., 13, 1611,

March 11, 2022:

THEMIS-ASI Auroral Beads selected as JGR cover:

Congrats to Nishimura et al. for their recent JGR paper being chosen for the cover. The research utilized simultaneous THEMIS ASI and satellite observations to explain how plasma flows create auroral beads, in the context of substorm auroral intensification.

Aurora in the night sky often begins with a sudden intensification called a substorm, and the auroral intensification shows a wave-like display (beads). It is critical to understand the origin of beads for revealing the mechanism of the sudden auroral intensifications, but it has been extremely difficult to find satellite observations in space to explore the magnetospheric source region of substorms.

Image shows an aurora which was observed by an all-sky camera at Fort Yukon, Alaska, at 9:14 UT on 20 November 2014. The image is projected onto the geographic map in Alaska. North is to the top and east is to the right. The image shows wave-like auroral structures called auroral beads. Credit: NASA/CSA/University of California, Berkeley/University of Calgary/NSF.

Nishimura et al. identified two simultaneous observations of auroral beads at the beginning of substorm auroral intensification, using all-sky imagers and related plasma dynamics by the THEMIS satellites in the plasma sheet. They found that the bead structure and propagation are related to charge accumulation and fast plasma streams in the plasma sheet. The plasma flow speed coincided with the bead speed, and the charge distribution and plasma stream direction reversed when the auroral beads moved in the opposite direction, giving strong evidence of the connection between the observations at the two locations. The plasma streams reduced the electric currents in the plasma sheet, and the paper suggests that the current reduction destabilizes the plasma sheet and initiates the substorm auroral intensification.

Citation: Nishimura, Y., Artemyev, A. V., Lyons, L. R., Gabrielse, C., Donovan, E. F., Angelopoulos, V. (2022). Space-ground observations of dynamics of substorm onset beads. Journal of Geophysical Research: Space Physics, 127, e2021JA030004.

October 6, 2021:

Researchers Find Standing Waves at Edge of Earth's Magnetic Bubble:

Congrats to Martin Archer et al. for their recent publication in Nature Communications. Using a combination of theory, THEMIS observations and global simulations, they discovered magnetopause standing waves propagating against the flow of the solar wind.

Earth sails the solar system in a ship of its own making: the magnetosphere, the magnetic field that envelops and protects our planet. The celestial sea we find ourselves in is filled with charged particles flowing from the Sun, known as the solar wind. Just as ocean waves follow the wind, scientists expected that waves traveling along the magnetosphere should ripple in the direction of the solar wind. But a new study reveals some waves do just the opposite.

An animated illustration of magnetospheric waves, in light blue. At the front of the magnetosphere, these waves appear to be still. Credits: M. Archer/E. Masongsong/NASA

Studying these magnetospheric waves, which transport energy, helps scientists understand the complicated ways that solar activity plays out in the space around Earth. Changing conditions in space driven by the Sun are known as space weather. That weather can impact our technology from communications satellites in orbit to power lines on the ground. “Understanding the boundaries of any system is a key problem,” said Martin Archer, a space physicist at Imperial College London who led the new study, published today in Nature Communications. “That’s how stuff gets in: energy, momentum, matter.”

Archer focuses on surface waves, meaning waves that require a boundary — in this case, the edge of the magnetosphere — to travel along. Previously, he and his colleagues established this boundary vibrates like a drum. When a strong burst of solar wind beats against the magnetosphere, waves race towards Earth’s magnetic poles and get reflected back.

The latest work considers the waves that form across the entire surface of the magnetosphere, using a combination of models and observations from NASA’s THEMIS mission, Time History of Events and Macroscale Interactions during Substorms.

The researchers found when solar wind pulses strike, the waves that form not only race back and forth between Earth’s magnetic poles and the front of the magnetosphere, but also travel against the solar wind. Archer likened these two kinds of movement to crossing a river: A boat can go from one riverbank to the other (traveling towards the poles) and upstream (against the solar wind). At the front of the magnetosphere, these waves appear to stand still.

The THEMIS satellites’ observations from within the magnetosphere first hinted some waves might be traveling against the solar wind. The researchers used models to illustrate how the energy of the wind coming from the Sun and that of the waves going against it could cancel each other out. It’s similar to what happens if you try walking up a downwards escalator. “It’s going to look like you’re not moving at all, even though you’re putting in loads of effort,” Archer said.

In this video, you can see and listen to standing waves at the edge of the magnetosphere. Data from the model has been translated into audio frequencies and stretched in time. The left panel shows a view looking down on Earth’s north pole. The right panel presents a view that slices through Earth’s magnetosphere, down the north and south poles. Red shows where the magnetic field grows stronger, while blue shows where it weakens. You first hear higher-frequency waves that are quickly replaced by a lower pitch — the standing waves that persist longer at the edge of the magnetosphere. Credits: Martin Archer/CCMC/NASA Download HD version from NASA SVS

These standing waves can persist longer than those that travel with the solar wind. That means they’re around longer to accelerate particles in near-Earth space, leading to potential impacts in the radiation belts, aurora, or ionosphere. Archer expects standing waves may occur elsewhere in the universe, from the magnetospheres of other planets to the peripheries of black holes. Studying the waves close to home can help scientists understand such distant boundaries.

By translating the wave models and data into the audible range, we can listen to the sound of these curious waves.

Tran, L., With NASA Data, Researchers Find Standing Waves at Edge of Earth’s Magnetic Bubble, NASA News, Oct. 6, 2021.

Dunning, H., When the solar wind hits Earth’s magnetosphere, a surprising stillness ensues, Imperial College London, Oct. 6, 2021.

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Archer, M. O., Hartinger, M. D., Plaschke, F., Southwood, D. J., Rastaetter, L. (2021), Magnetopause ripples going against the flow form azimuthally stationary surface waves, Nat. Comm., 12, 5697,

September 24, 2021:

Earth can make auroras without solar activity:

Congrats to Xu Zhang et al. for their feature on! Using THEMIS observations and statistical analyses, they revealed an atmospheric electron beam source for ECH waves, which in turn can power the diffuse aurora.

Diffuse auroras and the Big Dipper, photographed by Emmanuel V. Masongsong in Fairbanks, AK

No solar storms? No problem. Earth has learned to make its own auroras. New results from NASA’s THEMIS-ARTEMIS spacecraft show that a type of Northern Lights called "diffuse auroras" comes from our own planet–no solar storms required.

Diffuse auroras look a bit like pea soup. They spread across the sky in a dim green haze, sometimes rippling as if stirred by a spoon. They’re not as flamboyant as auroras caused by solar storms. Nevertheless, they are important because they represent a whopping 75% of the energy input into Earth’s upper atmosphere at night. Researchers have been struggling to understand them for decades.

“We believe we have found the source of these auroras,” says UCLA space physicist Xu Zhang, lead author of papers reporting the results in the Journal of Geophysical Research: Space Physics and Physics of Plasmas.

It is Earth itself.

Earth performs this trick using electron beams. High above our planet’s poles, beams of negatively-charged particles shoot upward into space, accelerated by electric fields in Earth’s magnetosphere. Sounding rockets and satellites discovered the beams decades ago. It turns out, they can power the diffuse auroras.

The video, below, shows how it works. The beams travel in great arcs through the space near Earth. As they go, they excite ripples in the magnetosphere called Electron Cyclotron Harmonic (ECH) waves. Turn up the volume and listen to the waves recorded by THEMIS-ARTEMIS:

THEMIS-E electric field wave burst mode (EFW) data converted to audio using real time and pitch, from nightside magnetosphere observations on June 1, 2011 16:06 UT. Low-energy electron beams (red) spray out of Earth’s north and south poles, converging in the equatorial magnetosphere (blue) to form Electron Cyclotron Harmonic waves (pink). The waves move Earthward, knocking other electrons (orange) out of orbit, which then fall back into the atmosphere to power the diffuse aurora (green). Video Credit, E. Masongsong UCLA EPSS, NASA Eyes Audio Credit, Martin O. Archer, Imperial College London, NASA HARP

ECH waves, in turn, knock other electrons out of their orbits, forcing them to fall back down onto the atmosphere. This rain of secondary electrons powers the diffuse auroras.

"This is exciting," says UCLA professor Vassilis Angelopoulos, a co-author of the papers and lead of the THEMIS-ARTEMIS mission. "We have found a totally new way that particle energy can be transferred from Earth’s own atmosphere out to the magnetosphere and back again, creating a giant feedback loop in space."

According to Angelopoulos, Earth’s polar electron beams1 sometimes weaken but they never completely go away, not even during periods of low solar activity. This means Earth can make auroras without solar storms.

The sun is currently experiencing periods of quiet as young Solar Cycle 25 sputters to life. Pea soup, anyone?

Source: Phillips, T., Earth Can Make Auroras Without Solar Activity,, Sept. 30, 2021.

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Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.-J. (2021), Beam-driven ECH waves: A parametric study, Phys. Plasmas, 28, 072902,

Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.‐J., Liu, J. (2021). Beam‐driven electron cyclotron harmonic waves in Earth’s magnetotail. Journal of Geophysical Research: Space Physics, 126, e2020JA028743.

August 7, 2021:

THEMIS analysis of K-H waves highlighted in AGU Eos Magazine:

DMSP Satellite Special Sensor Ultraviolet Spectrographic Imager on May 28, 2017 ~1:00 UT, depicting the auroral undulations that correlated to K-H waves detected by ground and space observatories. Credit NOAA, JHU APL.
Congratulations to Horvath and Lovell for their JGR Editor's Highlight! Their analysis of THEMIS data is the first to describe two separate geomagnetic storm events occurring in 2017 in which detected Kelvin-Helmholtz (K-H) waves on the magnetopause were observed to be correlated with surface waves in the hot zone of the outer plasmasphere. The Near-Earth Plasma Sheet (NEPS), activated by the K-H waves, acts as a resonator with eigenfrequencies in the Pc4-5 range, and leads to surface waves in the low-density hot zone of the outer plasmasphere.

K-H waves-related magnetic field (By) variations (from TH-E) correlated with the local geomagnetic By variations at Neumayer Station III and with the DMSP-F15 detections of auroral undulations (AUs, shaded cyan). Credit: Horvath and Lovell [2021], Figure 2h.

Observations confirm the coupling along magnetic field lines through field-aligned currents that link these high-altitude undulations to the auroral region. For one event a complex flow channel structure in the auroral regions was observed that appeared as sub-auroral ion drifts (SAIDs) early in the storm, and as sub-auroral polarization streams (SAPS) and abnormal SAIDs at later times. Observed wave structure embedded within the SAPS appeared to correlate well with the KH waves. The paper demonstrates the complex coupling that occurs over extremely large distances from the magnetopause to the auroral zones.

Source: Hickey, M. P., Satellite Data Reveal Magnetospause K-H Waves Impact Auroras, Eos, Aug. 5, 2021.

Citation: Horvath, I. and Lovell, B. C. (2021). Subauroral flow channel structures and auroral undulations triggered by Kelvin-Helmholtz waves. Journal of Geophysical Research: Space Physics, 126, e2021JA029144.

May 2, 2021:

THEMIS GBO and Arase observe a distant auroral electron acceleration mechanism:

Congrats to Shun Imajo et al. for their Science Reports paper "Active auroral arc powered by accelerated electrons from very high altitudes." Using THEMIS GBO in conjunction with Arase, they observed electron acceleration 30,000km above an auroral arc, a far greater distance for this process than previously expected.

A critical ingredient for auroras exists much higher in space than previously thought, according to new research in the journal Scientific Reports. The dazzling light displays in the polar night skies require an electric accelerator to propel charged particles down through the atmosphere. Scientists at Nagoya University and colleagues in Japan, Taiwan and the US have found that it exists beyond 30,000 kilometres above the Earth's surface -- offering insight not just about Earth, but other planets as well.

Schematic of the very high altitude electron acceleration powering an auroral arc. (a) Illustration in the meridional plane. (b) Illustration in the plane perpendicular to the background magnetic field. Credit: Shun Imajo, Nagoya Univ.

The story of aurora formation begins with supersonic plasma propelled from the Sun into space as high-speed, charged particles. When these charged particles get close to Earth, they are deflected and funnelled in streams along the planet's magnetic field lines, eventually flowing towards the poles. "Most electrons in the magnetosphere don't reach the part of the upper atmosphere called the ionosphere, because they are repelled by the Earth's magnetic field," explains Shun Imajo of Nagoya University's Institute for Space-Earth Environmental Research, the study's first author.

But some particles receive a boost of energy, accelerating them into Earth's upper atmosphere where they collide with and excite oxygen and nitrogen atoms at an altitude of about 100 kilometres. When these atoms relax from their state of excitation, they emit the auroral lights. Still, many details about this process remain a mystery. "We don't know all the details of how the electric field that accelerates electrons into the ionosphere is generated or even how high above Earth it is," Imajo says.

Scientists had assumed electron acceleration happened at altitudes between 1,000 and 20,000 kilometres above Earth. This new research revealed the acceleration region extends beyond 30,000 kilometres. "Our study shows that the electric field that accelerates auroral particles can exist at any height along a magnetic field line and is not limited to the transition region between the ionosphere and magnetosphere at several thousand kilometres," says Imajo. "This suggests that unknown magnetospheric mechanisms are at play."

The team reached this finding by examining data from THEMIS ground-based imagers in the US and Canada and from the electron detector on Arase, a Japanese satellite studying a radiation belt in Earth's inner magnetosphere. The data was taken from 15 September 2017 when Arase was at about 30,000 kilometres altitude and located within a thin active auroral arc for several minutes. The team was able to measure upward and downward movements of electrons and protons, ultimately finding the acceleration region of electrons began above the satellite and extended below it.

To further investigate this so-called very high-altitude acceleration region, the team next aims to analyse data from multiple aurora events, compare high-altitude and low-altitude observations, and conduct numerical simulations of electric potential. "Understanding how this electric field forms will fill in gaps for understanding aurora emission and electron transport on Earth and other planets, including Jupiter and Saturn," Imajo says.

Source: Nagoya Univ., The aurora's very high altitude booster, Science Daily, March 9, 2021.

Citation: Imajo, S., et al., (2021) Active auroral arc powered by accelerated electrons from very high altitudes. Scientific Reports, 11 (1) DOI: 10.1038/s41598-020-79665-5

April 23, 2021:

THEMIS observations used to improve solar flare and geospace models:

Congrats to Jing Liu et al. for their Nature Physics paper "Solar flare effects in the Earth's magnetosphere," using THEMIS observations in conjunction with magnetosphere-ionosphere-thermosphere modeling of solar flare impacts throughout geospace.

Researchers at Shandong University in China and the National Center for Atmospheric Research in the U.S. have recently carried out a study investigating the effects that solar flares can have on Earth's magnetosphere. Their paper, published in Nature Physics, offers new valuable insight that could pave the way towards a better understanding of geospace dynamics. Geospace, the portion of outer space that is closest to Earth, includes the upper atmosphere, ionosphere (i.e., the ionized part of the atmosphere) and magnetosphere.

An illustration of solar flare impacts on the whole geospace. Credit: Jing Liu.

"The magnetosphere is located in the region above the ionosphere and is the fully ionized space region above 1000 km from the ground," said Professor Jing Liu, lead author of the study. "The region is surrounded by the solar wind and is affected and controlled by the earth's magnetic field and the solar wind's magnetic field."

The magnetosphere is generally described as Earth's protective barrier against solar wind and other solar particles, as it prevents these particles from entering the planet's other protective layers. Nonetheless, past studies showed that when the direction of solar wind is opposite to the magnetosphere's magnetic field, magnetic lines from these two regions can 'connect." This means that some solar wind particles can be directly transmitted to the space surrounding Earth.

Liu and his colleagues analyzed data collected by different devices and satellites during a solar flare event that took place on 6 September 2017. To do this, they adopted a recently developed numerical geospace model developed at the National Center for Atmospheric Research. This model, called the high spatial-temporal resolution magnetosphere ionosphere thermosphere model, reproduces the changes triggered by solar flares in the magnetosphere-ionosphere coupling system. Using this model and previously collected THEMIS and other spacecraft data, the researchers were able to unveil solar flare effects on magnetospheric dynamics and on the electrodynamic coupling between the magnetosphere and the ionosphere. More specifically, they observed a rapid and large increase in flare-induced photoionization of the polar ionospheric E-region at altitudes between 90 and 150 km. The phenomenon observed by Liu and his colleagues appeared to have a number of effects on the geospace region, including a lower Joule heating of the Earth's upper atmosphere, a reconfiguration of the magnetosphere convection and changes in auroral precipitation.


Using the LTR model and previously collected data, the researchers were able to unveil solar flare effects on magnetospheric dynamics and on the electrodynamic coupling between the magnetosphere and the ionosphere. More specifically, they observed a rapid and large increase in flare-induced photoionization of the polar ionospheric E-region at altitudes between 90 and 150 km. The phenomenon observed by Liu and his colleagues appeared to have a number of effects on the geospace region, including a lower Joule heating of the Earth's upper atmosphere, a reconfiguration of the magnetosphere convection and changes in auroral precipitation.

"We demonstrated that solar flare effects extend throughout the geospace via electrodynamic coupling, and are not limited, as previously believed, to the atmospheric region where radiation energy is absorbed," Liu explained. "Due to the similar solar-magnetosphere-ionosphere coupling process in other earth-like planets, our study also provides new clues for exploring and understanding the effects of solar flares on other planets. In my future research, I plan to study the effects of flares on planets with the same magnetosphere (such as Jupiter, Venus and Saturn)."

Source: Fadelli, I., The effects of solar flares on Earth's magnetosphere,, April 23, 2021.

Citation: Liu, J., Wang, W., Qian, L., Lotko, Burns, A. G., Pham, K., Lu, G., Solomon, S. C., Wan, W., Anderson, B. J., Coster, A., Wilder, F. (2021) Solar flare effects in the Earth’s magnetosphere. Nat. Phys.,

August 14, 2020:

THEMIS probes reveal source process of auroral beads:

THEMIS observations by Panov et al. and new modeling results from APL's Sorathia et al. point to ballooning interchange instability as the magnetospheric source mechanism for auroral beads.

Aurora Mysteries Unlocked With NASA’s THEMIS Mission

Auroral beads photographed from the International Space Station Credit: NASA

A special type of aurora, draped east-west across the night sky like a glowing pearl necklace, is helping scientists better understand the science of auroras and their powerful drivers out in space. Known as auroral beads, these lights often show up just before large auroral displays, which are caused by electrical storms in space called substorms. Previously, scientists weren’t sure if auroral beads are somehow connected to other auroral displays as a phenomenon in space that precedes substorms, or if they are caused by disturbances closer to Earth’s atmosphere.

But powerful new computer models combined with observations from NASA’s Time History of Events and Macroscale Interactions during Substorms – THEMIS – mission have provided the first strong evidence of the events in space that lead to the appearance of these beads, and demonstrated the important role they play in our near space environment.

“Now we know for certain that the formation of these beads is part of a process that precedes the triggering of a substorm in space,” said Vassilis Angelopoulos, principal investigator of THEMIS at the University of California, Los Angeles. “This is an important new piece of the puzzle.”

By providing a broader picture than can be seen with the three THEMIS spacecraft or ground observations alone, the new models have shown that auroral beads are caused by turbulence in the plasma – a fourth state of matter, made up of gaseous and highly conductive charged particles – surrounding Earth. The results, recently published in the journals Geophysical Research Letters and Journal of Geophysical Research: Space Physics, will ultimately help scientists better understand the full range of swirling structures seen in the auroras.

“THEMIS observations have now revealed turbulences in space that cause flows seen lighting up the sky as of single pearls in the glowing auroral necklace," said Evgeny Panov, lead author on one of the new papers and THEMIS scientist at the Space Research Institute of the Austrian Academy of Sciences. “These turbulences in space are initially caused by lighter and more agile electrons, moving with the weight of particles 2000 times heavier, and which theoretically may develop to full-scale auroral substorms.”

To uncover the mysteries behind the formation of auroral beads, scientists combined measurements from NASA's THEMIS mission and ground observations with computer models. Credits: NASA's Goddard Space Flight Center
Mysteries of Auroral Beads Formation

Auroras are created when charged particles from the Sun are trapped in Earth’s magnetic environment – the magnetosphere – and are funneled into Earth’s upper atmosphere, where collisions cause hydrogen, oxygen, and nitrogen atoms and molecules to glow. By modelling the near-Earth environment on scales from tens of miles to 1.2 million miles, the THEMIS scientists were able to show the details of how auroral beads form.

As streaming clouds of plasma belched by the Sun pass Earth, their interaction with the Earth’s magnetic field creates buoyant bubbles of plasma behind Earth. Like a lava lamp, imbalances in the buoyancy between the bubbles and heavier plasma in the magnetosphere creates fingers of plasma 2,500 miles wide that stretch down towards Earth. Signatures of these fingers create the distinct bead-shaped structure in the aurora.

“There's been a realization that, all summed up, these relatively little transient events that happen around the magnetosphere are somehow important,” said David Sibeck, THEMIS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We have only recently gotten to the point where computing power is good enough to capture the basic physics in these systems.”

Now that scientists understand the auroral beads precede substorms, they want to figure out how, why and when the beads might trigger full-blown substorm. At least in theory, the fingers may tangle magnetic field lines and cause an explosive event known as magnetic reconnection, which is well known to create full-scale substorms and auroras that fill the nightside sky.

New Models Open New Doors

Since its launch in 2007, THEMIS has been taking detailed measurements as it passes through the magnetosphere in order to understand the causes of the substorms that lead to auroras. In its prime mission, THEMIS was able to show that magnetic reconnection is a primary driver of substorms. The new results highlight the importance of structures and phenomenon on smaller scales – those hundreds and thousands of miles across as compared to ones spanning millions of miles.

“In order to understand these features in the aurora, you really need to resolve both global and smaller, local scales. That's why it was so challenging up to now,” said Slava Merkin, co-author on one of the new papers and scientist at NASA’s Center for Geospace Storms headquartered at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “It requires very sophisticated algorithms and very big supercomputers.”

The new computer simulations almost perfectly match THEMIS and ground observations. After the initial success of the new computer models, THEMIS scientists are eager to apply them to other unexplained auroral phenomena. Particularly in explaining small-scale structures, computer models are essential as they can help interpret what happens in between the spaces where the three THEMIS spacecraft pass.

“There’s lots of very dynamic, very small-scale structures that people see in the auroras which are hard to connect to the larger picture in space since they happen very quickly and on very small scales,” said Kareem Sorathia, lead author on one of the new papers and scientist at NASA’s Center for Geospace Storms headquartered at Johns Hopkins Applied Physics Laboratory. “Now that we can use global models to characterize and investigate them, that opens up a lot of new doors.”

Source: Johnson-Groh, M. (2020), Aurora Mysteries Unlocked With NASA’s THEMIS Mission, NASA Goddard News, August 14, 2020.

Rehm, J. (2020), New Simulations Unravel Mystery Behind Aurora’s ‘String of Pearls’, JHU APL News, August 14, 2020.

Forbes Editor's Pick

Citation: Panov, E. V., Lu, S., & Pritchett, P. L. (2020). Understanding spacecraft trajectories through detached magnetotail interchange heads. Journal of Geophysical Research: Space Physics, 125, e2020JA027930.

Sorathia, K. A., Merkin, V. G., Panov, E. V., Zhang, B., Lyon, J. G., & Garretson, J., et al. (2020). Ballooning‐interchange instability in the near‐Earth plasma sheet and auroral beads: Global magnetospheric modeling at the limit of the MHD approximation. Geophysical Research Letters, 47, e2020GL088227.

January 13, 2020:

THEMIS observes nightside reconnection as power source of magnetic storm:

New THEMIS study finds that reconnection during storms can get much closer to Earth than previously thought, from where it can power storms directly. By feeding the ring current directly, this creates a qualitatively different mode of magnetospheric convection.

Magnetic storms originate closer to Earth than previously thought, threatening satellites

An illustration shows the Earth’s magnetosphere during a magnetic storm. At right, three satellites witnessed reconnection close to geosynchronous orbit where many other critical satellites reside. The red “X” identifies the reconnection site, and the yellow arrows indicate the direction of explosive outflows of energized particles toward and away from Earth. Earth-directed electrons (shown in red and pink) carry energy along magnetic field lines to power the aurora at Earth’s north and south poles. These energized electrons were detected by a weather satellite (center). Credit: E. Masongsong/UCLA EPSS

Beyond Earth’s atmosphere are swirling clouds of energized particles — ions and electrons — that emanate from the sun. This “solar wind” buffets the magnetosphere, the magnetic force field that surrounds Earth. In much the same way winds and storms create weather in our atmosphere, strong gusts of solar wind penetrating the magnetosphere can generate magnetic storms with powerful electric currents that can impact our lives.

A recent study in Nature Physics by Angelopoulos et al. shows that such storms can originate much that such storms can originate much closer to Earth than previously thought, overlapping with the orbits of critical weather, communications and GPS satellites.

Brilliant aurora borealis captured over Yukon, Canada, during a geomagnetic storm. Its elusive driver, magnetic reconnection, was captured by a fleet of spacecraft near local midnight, with a large energy release surprisingly close to geosynchronous orbit. Credit: Joseph Bradley

Magnetic storms can produce dazzling northern lights or hazardous particles careening toward spacecraft and astronauts, zapping them out of commission. Under certain conditions, magnetic storms can disable the electrical grid, disrupt radio communications and corrode pipelines, even creating extreme aurora visible close to the equator. “By studying the magnetosphere, we improve our chances of dealing with the greatest hazard to humanity venturing into space: storms powered by the sun,” Angelopoulos said.

An incident that illustrates the dramatic power of magnetic storms occurred in 1921, when such a storm disrupted telegraph communications and caused power outages that resulted in a New York City train station burning to the ground. And in 1972 the Apollo 16 and 17 astronauts narrowly missed what could have been a lethal solar eruption. These incidents underscore the potential dangers that should be assessed as more humans venture into orbit. If a similar storm occurred today, a separate study estimated, economic losses in the U.S. due to electrical blackouts only could surpass $40 billion a day.

How electric currents in space influence the aurora and magnetic storms has been long debated in the space physics community. Because the storms occur so rarely and satellite coverage is sparse, it has been difficult for researchers to detect the dynamic process that powers those storms. When solar wind magnetic energy is transferred into the magnetosphere, it builds up until it is converted into heat and particle acceleration through a process called magnetic reconnection. After decades of study, it is still unclear to researchers where exactly magnetic reconnection occurs during storms.

Mosaic of THEMIS auroral all-sky cameras, imaging the night sky across Canada during the magnetic storm studied in the paper. Like a TV screen, the aurora reveals otherwise invisible particles and electrical currents arriving from space, causing the upper atmosphere to glow. Magnetic “footpoints” of orbiting THEMIS spacecraft (shown as blue, cyan and magenta squares, GOES weather satellite in yellow) correspond to their location in the magnetosphere, showing their close proximity to the storm’s origin. Moon light contamination shown using white arrows, blue line indicates midnight, magnetic local time. Credit: THEMIS ASI, Yukitoshi Nishimura, Boston University.

Recent observations by multiple satellites have shown that magnetic storms can be initiated by magnetic reconnection much closer to Earth than previously thought possible. The three NASA THEMIS satellites observed magnetic reconnection only about three to four Earth diameters away. The researchers did not expect this could happen in the comparatively stable magnetic field configuration near Earth.Later, a weather satellite, which was nearer to Earth in geostationary orbit, detected energized particles associated with magnetic storms.

The weather satellite proved that this near-Earth reconnection stimulated ion and electron acceleration to high energies, posing a hazard to hundreds of satellites operating in this common orbit. Such particles can damage electronics and human DNA, increasing the risk of radiation poisoning and cancer for astronauts. Some particles can even enter the atmosphere and affect airline passengers.

“Only with such direct measurements of magnetic reconnection and its resulting energy flows could we convincingly prove such an unexpected mechanism of storm power generation,” said Angelopoulos, who is lead author of the paper. “Capturing this rare event, nearer to Earth than ever detected before, forces us to revise prior assumptions about the reconnection process.”

This discovery will ultimately help scientists refine predictive models of how the magnetosphere responds to solar wind, providing precious extra hours or even days to prepare satellites, astronauts and the energy grid for the next “big one” in space.

Source: Masongsong, E. (2020), Researchers discover a new source of space weather – too close to home, UCLA Newsroom, January 13, 2020.

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Citation: Angelopoulos, V., Artemyev, A.V., Phan, T.D., Miyashita, Y. (2019), Near-Earth magnetotail reconnection powers space storms. Nat. Phys. doi:10.1038/s41567-019-0749-4

September 2, 2019:

THEMIS diffuse aurora findings on GRL cover, Editor's Highlight, NASA News:

Congrats to N. Sivadas et al., whose paper on structured diffuse aurora was selected as the GRL cover, an AGU highlight, and NASA News story. Using THEMIS probes, ASI/GBO, and NOAA satellite data, they linked this aurora to its source region in the radiation belts.

Streaks in Aurora Found to Map Features in Earth’s Radiation Environment

A special kind of streaked aurora has been found to track disturbances in near-Earth space from the ground. Known as structured diffuse aurora, it was recently discovered, with the help of NASA spacecraft and instruments, that these faint lights in the night sky can map the edges of the Van Allen radiation belts — hazardous concentric bands of charged particles encircling Earth.

When the Van Allen belts undulate in shape and size — which they do in response to incoming radiation from the Sun as well as changes from Earth below — they can envelop satellites in unexpected radiation. The new discovery, reported in the AGU journal Geophysical Research Letters, will help us better track the edges of the belts — and the more we know about how the belts are changing, the more we can mitigate such effects.

A white light camera at Poker Flat shows the structured diffuse aurora, that mark the edge of the Van Allen radiation belt as it dances across the night sky. Using a combination of instruments and spacecraft, scientists were able to determine where the electrons causing the aurora had originated. Credits: NASA/Nithin Sivadas

The road to linking these auroras to the Van Allen belts began with a blob seen in radar data. Scientists spotted the unexpected blob, caused by an excess of electrons, in radar data from Poker Flat, a research facility and rocket range in Alaska – and they set out to find its origin. Using a group of instruments — including NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, NOAA-17 (a low-Earth orbit spacecraft), and radar and optical instruments on the ground at Poker Flat — the scientists were able to track back to the electrons’ source.

An unexpected blob, circled in green, seen in radar data from Poker Flat sparked the research leading to the discovery of the structured diffuse aurora as maps of the edge of the outer Van Allen belt. Credits: NASA/Nithin Sivadas

They did this by looking at the energies of the electrons. Electrons coming from the outer Van Allen belt have high energies that decrease farther away from Earth. The scientists worked out where these electrons had been by mapping their trajectories and working backwards. Measurements from the NOAA-17 satellite along the trajectory confirmed that the streaked aurora, which was visible during the blob event, ultimately maps to the edge of the outer Van Allen belt.

This illustration shows the white-light observations of the fine structure in the aurora superimposed over Alaska. The dots signifying electrons are color coded to show their origins, with red dots indicating electrons from the radiation belts and blue from further out. Credits: NASA/Google Earth/Nithin Sivadas

The scientists found the electrons had been knocked loose from the outer Van Allen belts as Earth’s magnetic environment was squeezed before the onset of what’s known as a substorm — a space weather event on the night side of Earth triggered by an onslaught of charged particles from the Sun. Eventually, the electrons made their way down into the atmosphere, where they manifested as streaks in the aurora.

This schematic of the Van Allen belts’ structure, shows the region of the structured diffuse aurora and the outer edge of the Van Allen belts that it maps. Credits: NASA’s Goddard Space Flight Center/ Historic image of Van Allen Belts courtesy of NASA’s Langley Research Center/ Nithin Sivadas

Scientists will now be able to watch structured diffuse aurora from the ground in real-time to better understand how the edge of the outer Van Allen belt is changing — something that previously could only be done intermittently by waiting for a spacecraft to fly under the belt.

Source: Johnson-Groh, Mara (2019), Streaks in Aurora Found to Map Features in Earth’s Radiation Environment, AGU GeoSpace Blog, August 27, 2019. and NASA Goddard News Link

Citation: Sivadas, N., Semeter, J., Nishimura, Y. T., & Mrak, S. ( 2019). Optical signatures of the outer radiation belt boundary. Geophysical Research Letters, 46, 8588– 8596.

August 9, 2019:

THEMIS shock wave acceleration on

A New Source of Space Radiation

Astronauts are surrounded by danger: hard vacuum, solar flares, cosmic rays. Researchers from UCLA have just added a new item to the list. Earth itself.

“A natural particle accelerator only 40,000 miles above Earth’s surface is producing ‘killer electrons’ moving close to the speed of light,” says Terry Liu, a newly-minted PhD who studied the phenomenon as part of his thesis with UCLA Prof. Vassilis Angelopoulos.

This means that astronauts leaving Earth for Mars could be peppered by radiation coming at them from behind–from the direction of their own home planet.

Overview of the shock wave discovered near Earth, including a simulation of the upstream bowshock region observed by THEMIS. Credit: E. Masongsong, UCLA EPSS

NASA’s THEMIS spacecraft ran across the particles in 2008 not far from the place where the solar wind slams into Earth’s magnetic field. Researchers have long known that shock waves at that location could accelerate particles to high energies–but not this high. The particles coming out of the Earth-solar wind interface have energies up to 100,000 electron volts, ten times greater than previously expected.

How is this possible? Liu found the answer by combining THEMIS data with computer simulations of the sun-Earth interface. When the solar wind meets Earth, it forms a shock wave around Earth’s magnetic field, shaped like the bow waves that form ahead of a boat moving through water. Within this “bow shock” immense stores of energy can be abruptly released akin to the sonic boom of an airplane.

Liu found that some electrons are shocked not just once, but twice or more, undergoing mirror-like reflections within the bow shock that build energy to unexpected levels. Most of the boosted particles shoot back into space away from Earth.

Above: Dr. Terry Liu created this diagram showing the location of the natural particle accelerator and how it sprays radiation into space.

“Similar particles have been detected near Saturn, suggesting that the process is at work there as well,” says Liu. “Indeed,” adds Angelopoulos, “this type of particle acceleration could be happening throughout the cosmos–from supernovas to solar storms–wherever a supersonic wind hits a barrier.”

Meanwhile, back home, Earth-orbiting satellites and departing astronauts have a new source of radiation to contend with. It’s right over their shoulder.

Source: Phillips, Tony (2019). A New Source of Space Radiation,, August 9, 2019.

Citation: Liu, T.Z., V. Angelopoulos and S. Lu (2019), Relativistic electrons generated at Earth's quasi-parallel bow shock, Science Advances, 5:7, eaaw1368. DOI: 10.1126/sciadv.aaw1368

August 1, 2019:

2019 Recipient of SPA/AGU Fred L. Scarf Award:

Congrats to Terry Z. Liu who won this year’s AGU best Space Physics and Aeronomy section Ph.D. thesis Fred Scarf award! Terry used THEMIS/ARTEMIS data, providing the most appropriate instrumentation and time and space scales, to reveal the properties and physical processes of Foreshock Transients, including their contribution to particle acceleration at shock environments. It comes with an invited AGU talk and a stipend. See: and the announcement in EOS: . Terry is getting ready to begin his two-year Jack Eddy postdoctoral fellowship at the U. of Alaska this Fall, to study magnetic reconnection and particle acceleration at foreshock transients using THEMIS and MMS.

July 1, 2019:

STEVE selected as JGR cover image:

Cover image shows a purple white subauroral arc with green rayed emission appearing either below or laterally displaced from the white/purple arc on the left separated from the green aurora on the right. Image DSC2483 was taken with Nikon D810 camera looking eastward (north to the right) on 1 September 2016 at 0032 UT at location 51.7255°N, 116.5227°W Peyto Lake Alberta, Canada. (Exposure 20 s at F/2.8 and the equivalent focal length was 15 mm with ISO speed of 5,000.)

Congrats to S.B. Mende and C. Turner for their recent JGR paper being chosen for the cover. The image is of STEVE, the Strong Thermal Emission Velocity Enhancement, taken with a DSLR CMOS sensor camera calibrated to yield the relative wavelengths of the auroral phenomena. Using the GLOW computer model, their analyses confirmed that the purple emission includes a unique wavelength corresponding to N2+ ions, caused by a different source mechanism from the green picket fence or the typical aurora. This work was supported at UC Berkeley by THEMIS NAS5-02099.

Citation: Mende, S. B., & Turner, C. (2019). Color ratios of subauroral (STEVE) arcs. Journal of Geophysical Research: Space Physics, 124, 5945– 5955.

June 16, 2019:

STEVE selected as GRL cover image:

Amateur astronomer's photograph that shows the STEVE phenomenon. Image credit: Thomas Spence, reproduced with permission.

Congrats to Toshi Nishimura et al. for their recent GRL paper being chosen for the cover. The research was dependent on THEMIS satellite observations, as well as high-resolution images acquried by "citizen scientists." These intrepid auroral photographers are well-equipped to document the STEVE phenomenon with precise date and location stamps that can be used for data analysis. They also photograph regions where there are no all-sky cameras, so their searchable images on social media make it easy for researchers to find useful events.

The photograph was taken at 4 UT on 6 May 2018 in Tofte, MN. The major structures are two bands of upper atmospheric emissions, a purple arc and green picket fence. Green aurora is also seen near the horizon to the right (north). The starlight and aurora reflect on a lake.

Citation: Nishimura, Y., Gallardo-Lacourt, B., Zou, Y., Mishin, E., Knudsen, D. J., Donovan, E. F., et al (2019). Magnetospheric signatures of STEVE: Implication for the magnetospheric energy source and inter-hemispheric conjugacy. Geophysical Research Letters, 46.

April 25, 2019:

THEMIS observations enable discovery of STEVE magnetospheric source:

Amateur astronomer’s photograph used in the new research. The photograph was taken on 8 May 2016 in Keller, Washington The major structures are two bands of upper atmospheric emissions 160 kilometers (100 miles) above the ground, a mauve arc and green picket fence. The black objects at the bottom are trees. The background star constellations include Gemini and Ursa Major. Credit: Rocky Raybell.

Congrats to Toshi Nishimura et al. for their AGU press release and National Geographic feature on their paper "Magnetospheric signatures of STEVE: Implication for the magnetospheric energy source and inter-hemispheric conjugacy" using THEMIS, ground-based imagers, and citizen scientist observations.

Last year, the obscure atmospheric lights became an internet sensation. Typical auroras, the northern and southern lights, are usually seen as swirling green ribbons spreading across the sky. But STEVE is a thin ribbon of pinkish-red or mauve-colored light stretching from east to west, farther south than where auroras usually appear. Even more strange, STEVE is sometimes joined by green vertical columns of light nicknamed the “picket fence.”

Auroras are produced by glowing oxygen and nitrogen atoms in Earth’s upper atmosphere, excited by charged particles streaming in from the near-Earth magnetic environment called the magnetosphere. Scientists didn’t know if STEVE was a kind of aurora, but a 2018 study found its glow is not due to charged particles raining down into Earth’s upper atmosphere.

The authors of the 2018 study dubbed STEVE a kind of “sky-glow” that is distinct from the aurora, but were unsure exactly what was causing it. Complicating the matter was the fact that STEVE can appear during solar-induced magnetic storms around Earth that power the brightest auroral lights.

Authors of a new study published in AGU’s journal Geophysical Research Letters analyzed satellite data and ground images of STEVE events and conclude that the reddish arc and green picket fence are two distinct phenomena arising from different processes. The picket fence is caused by a mechanism similar to typical auroras, but STEVE’s mauve streaks are caused by heating of charged particles higher up in the atmosphere, similar to what causes light bulbs to glow.

“Aurora is defined by particle precipitation, electrons and protons actually falling into our atmosphere, whereas the STEVE atmospheric glow comes from heating without particle precipitation,” said Bea Gallardo-Lacourt, a space physicist at the University of Calgary and co-author of the new study. “The precipitating electrons that cause the green picket fence are thus aurora, though this occurs outside the auroral zone, so it’s indeed unique.”

Images of STEVE are beautiful in themselves, but they also provide a visible way to study the invisible, complex charged particle flows in Earth’s magnetosphere, according to the study’s authors. The new results help scientists better understand how particle flows develop in the ionosphere, which is important goal because such disturbances can interfere with radio communications and affect GPS signals.

Where does STEVE come from?

In the new study, researchers wanted to find out what powers STEVE and if it occurs in both the Northern and Southern Hemispheres at the same time. They analyzed data from several satellites passing overhead during STEVE events in April 2008 and May 2016 to measure the electric and magnetic fields in Earth’s magnetosphere at the time.

The researchers then coupled the satellite data with photos of STEVE taken by amateur auroral photographers to figure out what causes the unusual glow. They found that during STEVE, a flowing “river” of charged particles in Earth’s ionosphere collide, creating friction that heats the particles and causes them to emit mauve light. Incandescent light bulbs work in much the same way, where electricity heats a filament of tungsten until it’s hot enough to glow.

Artist’s rendition of the magnetosphere during the STEVE occurrence, depicting the plasma region which falls into the auroral zone (green), the plasmasphere (blue) and the boundary between them called the plasmapause (red). The THEMIS and SWARM satellites (left and top) observed waves (red squiggles) that power the STEVE atmospheric glow and picket fence (inset), while the DMSP satellite (bottom) detected electron precipitation and a conjugate glowing arc in the southern hemisphere. Credit: Emmanuel Masongsong, UCLA, and Yukitoshi Nishimura, BU/UCLA.

Interestingly, the study found the picket fence is powered by energetic electrons streaming from space thousands of kilometers above Earth. While similar to the process that creates typical auroras, these electrons impact the atmosphere far south of usual auroral latitudes. The satellite data showed high-frequency waves moving from Earth’s magnetosphere to its ionosphere can energize electrons and knock them out of the magnetosphere to create the striped picket fence display.

The researchers also found the picket fence occurs in both hemispheres at the same time, supporting the conclusion that its source is high enough above Earth to feed energy to both hemispheres simultaneously.

Public involvement has been crucial for STEVE research by providing ground-based images and precise time and location data, according to Toshi Nishimura, a space physicist at Boston University and lead author of the new study.

“As commercial cameras become more sensitive and increased excitement about the aurora spreads via social media, citizen scientists can act as a ‘mobile sensor network,’ and we are grateful to them for giving us data to analyze,” Nishimura said.

Source: Lipuma, L. (2019), Scientists discover what powers celestial phenomenon STEVE.

National Geographic

Science Friday

Popular Mechanics

NSF Discovery News

Citation: Nishimura, Y., Gallardo-Lacourt, B., Zou, Y., Mishin, E., Knudsen, D. J., Donovan, E. F., et al (2019). Magnetospheric signatures of STEVE: Implication for the magnetospheric energy source and inter-hemispheric conjugacy. Geophysical Research Letters, 46.

April 17, 2019:

Two THEMIS Featured Articles in JGR Space Physics and Eos:

San Lu’s paper on the origin and asymmetric distribution of the Hall electric field in Earth’s thin magnetotail current sheet, shows in simulations and observations with THEMIS and MMS how the thin current sheet and its characteristic normal electric field (Ez, pointing towards the center) develops asymmetrically across the tail (stronger at the dusk sector). This explains (at least in part) why substorms, injections, plasmoids etc develop also asymmetrically in the magnetosphere.

Citation: Lu, S., Artemyev, A. V., Angelopoulos, V., Lin, Y., Zhang, X.-J., Liu, J., Avanov, L., Giles, B.L., Russell, C.T., Strangeway, R.J. (2019). The Hall electric field in Earth's magnetotail thin current sheet. Journal of Geophysical Research: Space Physics, 124.

Grant Stephen’s paper was also selected as a Research Spotlight in Eos magazine. Using an empirical (model) picture of substorm current wedge development, they show the redistribution of the magnetospheric current systems during growth phase and expansion of a magnetospheric substorm. THEMIS being equatorial and often crossing the peak of the cross-tail current density contributed greatly to model development and validation (amongst a large volume of magnetic data from a number of satellites).

Eos Research Spotlight: Zastrow, M. (2019), Data mining reveals the dynamics of auroral substorms, Eos, 100,

Citation: Stephens, G. K., Sitnov, M. I., Korth, H., Tsyganenko, N. A., Ohtani, S., Gkioulidou, M., Ukhorskiy, A. Y. (2019). Global Empirical Picture of Magnetospheric Substorms Inferred from Multi-Mission Magnetometer Data. Journal of Geophysical Research: Space Physics, 124.

March 15, 2019:

Statistical study of STEVE using THEMIS All-Sky data highlighted in Eos magazine:

Researchers find a violent potential origin for the aurora-like phenomenon dubbed STEVE events, pictured here in southern Alberta. Credit: Alan Dyer

Earlier this year, researchers announced that long, narrow streaks of purple light occasionally observed in the nighttime sky are not a new type of aurora, as first suspected, but a novel upper atmospheric phenomenon. Dubbed Strong Thermal Emission Velocity Enhancement (STEVE) because of their association with fast-moving ions and hot electrons in Earth’s ionosphere, these celestial lights are often visible at lower latitudes than most auroras and appear to be caused by a different, and still undetermined, mechanism.

To better characterize STEVE, Gallardo-Lacourt et al. conducted the first statistical analysis of this optical phenomenon. Using NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground-based All-Sky Imager array and the Canadian Space Agency’s Redline Geospace Observatory (REGO) databases, the team identified and analyzed optical data from 28 STEVE events that occurred between December 2007 and December 2017.

According to the results, STEVE is quite narrow, averaging only about 20 kilometers in the north–south direction, but typically stretches more than 2,100 kilometers east–west across the sky. The events usually last about an hour, and all but one shifted closer to the equator throughout its duration, motion the authors suggest could be attributed to the expansion of the high-latitude convection zone toward the equator.

To determine the geomagnetic conditions that favor STEVE’s formation, the team analyzed a variety of space weather indices and geophysical parameters for the hours surrounding each event. The results indicate that STEVE typically occurs about 1 hour after the inception of substorms (violent disturbances during which energy from Earth’s magnetic tail is injected into the ionosphere’s high latitudes), especially those with long expansion phases. This study represents an important step toward understanding the nature and origin of this interesting phenomenon, which has the potential to offer fresh insights into Earth’s complex magnetospheric system.

Source: Cook, T. (2019), Probing the origin of a new celestial phenomenon, Eos, 100,

Citation: Gallardo-Lacourt, B., Nishimura, Y., Donovan, E., Gillies, D. M., Perry, G. W., Archer, W. E., Nava, O. A., Spanswick, E. L. (2018), A statistical analysis of STEVE. Journal of Geophysical Research: Space Physics, 123, 9893– 9905.

February 22, 2019:

THEMIS featured on iconic TV game show, Jeopardy:

Credit: Tony Mercer, UCB SSL

A few days after the mission's 12th anniversary, THEMIS achieved a new level of recognition in popular culture after being chosen as a clue on the hit TV game show, Jeopardy. It aired on February 22, 2019 on the Jeopardy All-Stars edition, under the category "The Arctic" for $800. Unfortunately, Alex Trebek mispronounced it as "THEE-mis," though the contestant did get it correct! (What is... aurora borealis)

February 12, 2019:

THEMIS article in Nature Communications confirms magnetopause standing waves:

Congrats to Martin Archer et al. for their publication "Direct observations of surface eigenmode of the dayside magnetopause" published today in Nature Communications, along with an impressive NASA press release. The paper presents the first evidence of magnetopause standing waves, which were clearly excited by a high-speed jet.

Illustration of a plasma jet impact (yellow) generating standing waves at the boundary (blue) of Earth's magnetic shield (green). Credit: E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU

Space isn't silent. In fact, an entire orchestra of instruments fills our near-Earth environment with eerie sounds. Scientists have long known about space phenomena involving electromagnetic waves travelling around Earth that resonate like string instruments and whistle like wind instruments. Now, new research published in Nature Communications has added a percussive member to the cosmic ensemble: a giant drum, triggered by plasma jets striking the boundary of the protective magnetic bubble surrounding our planet.

This magnetic bubble, known as the magnetosphere, is encased by a boundary region known as the magnetopause, our first barrier to high-energy particles coming from the Sun. At the magnetopause, the majority of solar particles are deflected around Earth, but under certain conditions some sneak through. Understanding the mechanics of the magnetopause is key to helping keep our satellites, telecommunications and astronauts safe from the potentially harmful radiation these particles bring.

NASA's THEMIS mission proves a 45-year old theory that the outer boundary of Earth's magnetic field vibrates like a drum. Credits: Martin Archer, Queen Mary University of London

Using data from NASA's Time History of Events and Macroscale Interactions during Substorms, or THEMIS, mission, the scientists discovered ­that when the magnetopause is struck by a jet of plasma from the Sun, it vibrates like a drum, with waves echoing back and forth along its surface, much like they do on top of a drumhead. The new discovery comes several decades after such behavior was first theorized.

"Given the lack of evidence over the 45 years since they were proposed, there had been speculation that these drum-like vibrations might not occur at all," said Martin Archer, space physicist at Queen Mary University of London and lead author of the new paper. "Now we see that waves on the magnetopause's surface reflect between two points near the magnetic poles — acting very much like a drum."

Inside the magnetosphere, scientists have long been listening in on space sounds created by various electromagnetic waves. This veritable orchestra of waves can be heard as sound when processed correctly, and they even exhibit similar behaviors to certain musical instruments. So-called magnetosonic waves pulse through plasma in the same way sound bounces through wind instruments. Another type of wave, known as an Alfvén wave, resonates along magnetic field lines, just like string instruments' vibrating strings. While both of these types of waves can travel anywhere in space, the newly discovered waves are a type of surface waves — waves that require some sort of boundary to travel along.

In this case the magnetopause acted as the boundary. When a plasma jet — the drumstick — strikes the magnetopause, surface waves form a standing wave pattern — where the ends appear to be standing still while other points vibrate back and forth — just like a drumhead. The fixed points in the wave, which are the rim or edge of the drum, are near Earth's magnetic poles; the waves vibrate the surface of the magnetopause in between. While the wave itself remains on the surface, the vibrations ultimately work their way down into the magnetosphere and trigger other types of waves. "The waves likely penetrate far into the inner magnetosphere causing ultra-low frequency waves, which affect things like radiation belts, the aurora, and even the ionosphere," Archer said.

The signals recorded by the THEMIS probes converted to audible sound. Credits: Video courtesy Martin Archer, Queen Mary University of London

The new study used data from the THEMIS mission, which initially used five identical probes to determine what physical process in near-Earth space initiates the auroras. "The authors make great use of observations from a time early in the mission when the spacecraft followed each other along their mutual orbit like pearls on a string," said David Sibeck, THEMIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "In this fortunate case, the THEMIS spacecraft were in just the right place to see the drumstick and hear the drum."

The scientists plan to look through archival THEMIS data for more of these events around Earth and determine how often the magnetopause may be booming like a drum. This research may also help provide insights into how to look for this phenomenon at other planets with magnetospheres, like Jupiter and Saturn, and what effect they may have in those systems.

Nature press release: Earth's Magnetic Field Booms Like a Drum, But No One Can Hear It

NASA press release: In Solar System's Symphony, Earth's Magnetic Field Drops the Beat

Citation: Archer, M. O., H. Hietala, M. D. Hartinger, F. Plaschke, V. Angelopoulos (2019). Direct observations of a surface eigenmode of the dayside magnetopause, Nature Communications, 10, 615,

December 13, 2018:

Two THEMIS research articles featured on JGR Space Physics website:

Illustration of Pi2 generation mechanisms proposed in the literature. Credit, Takahashi, et al., JGR 2018.

Roles of Flow Braking, Plasmaspheric Virtual Resonances, and Ionospheric Currents in Producing Ground Pi2 Pulsations

K. Takahashi et al. showed that plasma flows in the nightside magnetosphere can ring the inner magnetosphere like a bell, using multiple satellites including THEMIS, ground-based magnetometers, and numerical simulations. Focusing on transient magnetic field and plasma flow variations with periods of about one minute, or Pi2 waves, Takahashi et al. combined observations from many spatial locations to show that nightside plasma flows are capable of exciting a wide range of Pi2 wave periods. However, only certain periods were observed in the inner magnetosphere, much like a bell can only be rung at a certain pitch. Numerous models have been proposed to explain the source of Pi2 waves in the inner magnetosphere, and the relative importance of each model remains an open question. The observations and numerical simulations in this work validate one model, the "plasmaspheric virtual resonance," that predicts how the entire inner magnetosphere responds to rapidly varying, spatially localized plasma flows at specific Pi2 periods.

Citation: Takahashi, K., Hartinger, M. D., Vellante, M., Heilig, B., Lysak, R. L., Lee, D.-H., & Smith, C. W. (2018). Roles of flow braking, plasmaspheric virtual resonances, and ionospheric currents in producing ground Pi2 pulsations. Journal of Geophysical Research: Space Physics, 123, 9187–9203.

Polar diagrams of the model field-aligned current distribution at the ionospheric altitude, for three values of IMF By=5nT (left column), By=0 (center column), and By=−5nT (right column) and three intervals of IMF Bz: 2≤Bz≤6nT (top row), |Bz|≤2nT (middle row), and −6≤Bz≤−2nT (bottom row). Red and blue colors indicate the upward and downward field-aligned current direction. IMF = interplanetary magnetic field. Credit Tsyganenko & Andreeva, JGR 2018.

Empirical Modeling of Dayside Magnetic Structures Associated With Polar Cusps

This work by Tsyganenko and Andreeva deals with the solar windward side of the Earth's magnetosphere, which is most exposed to the incoming flow of interplanetary plasma, and, as such, takes the first blow during space storms. The Earth's magnetic field interconnects there with the field carried from Sun, which results in a complex system of electric currents flowing along the magnetic field lines down to the ionosphere and then back into the interplanetary space. These currents conduct the solar wind momentum and energy into the magnetosphere and are sensitive to the orientation of the interplanetary magnetic field. Another unique feature of the dayside magnetosphere is a pair of deep funnel-shaped holes on its boundary, called polar cusps, a kind of weak spots where the solar wind plasma is injected into the magnetosphere and suppresses the local magnetic field. In spite of huge amount of data collected since the beginning of the space era, these factors have not yet been properly included in the existing models, and the present paper describes an attempt to fill this gap. Based on large sets of spacecraft data and novel techniques, they developed a new model which incorporates and quantitatively describes both the above features.

Citation: Tsyganenko, N. A., & Andreeva, V. A. (2018). Empirical modeling of dayside magnetic structures associated with polar cusps. Journal of Geophysical Research: Space Physics, 123, 9078–9092.

October 18, 2018:

GOES and THEMIS wave data support successful Citizen Science research:

High school students listening to audio tracks of NOAA satellite data have identified the sounds of solar storms buffeting Earth's magnetic field. The results of a UK-led citizen science project suggest that the approach of converting physical data into sound signals could help NOAA and other scientists make sense of massive amounts of data from satellites and other instruments. Their findings were published in Space Weather, a journal of the American Geophysical Union.

Dr. Martin Archer (second from the right) with students from Eltham Hill School and Professor David Berman from Queen Mary University of London.

Lead author Martin Archer, a scientist at Queen Mary University of London, took 10 years of ultra-low frequency (ULF) magnetic wave measurements in Earth's magnetosphere gathered by NOAA's GOES-series satellites. The data came from 2007–08 and 2010–17. He converted those measurements into audio files by changing the sampling rate—playing back the raw data files so quickly that they were audible to humans. This process is called sonification. In that data conversion, one year of raw data became six minutes of audio. "The audio format allows us to get through a lot of data just by listening to it," Archer says.

One big advantage of converting ULF data into sound is that people are much better at finding a signal in noisy data by hearing it rather than seeing it. So a dataset on a plot might look undistinguished, but converting those data into sound might reveal patterns worth exploring. "Our ears are better at picking out tones than some of the mathematical techniques we use, particularly when other sounds or lots of noise are also present," Archer says.

Spectrogram view of the GOES-13 stereo audio file of ULF wave data gathered between September 29 and October 12, 2013. Credit: Martin Archer/Queen Mary University of London

Earth's magnetic shield, which protects against harmful radiation from the sun and more distant sources, is full of ultra-low frequency waves. These waves transfer energy from outside Earth's magnetic shield to regions inside it. And, they play a key role in creating the impacts of space weather—including geomagnetic storms that can damage power grids, impact GPS, create communications challenges for passenger airlines and mobile telephones, and more. The frequency of those waves ranges from fractions of a millihertz (mHz) up to just 1 hertz (Hz). One thousand mHz equals 1 Hz—a much lower frequency than the range of human hearing. "Ultra-low frequency waves are too low-pitch for us to hear, but we can make our satellite recordings of them audible by dramatically speeding up their playback with audio software," says Dr. Archer. The audio data are now publicly available.

As an example of what is possible with this approach, a group of 12th year physics students from Eltham Hill school in London used the sonified GOES data to identify poloidal narrowband ULF waves whose frequency decreased over multiple of days. THEMIS multiprobe data were critical to the study, used to identify and confirm the source of the waves. The event occurred during the recovery phase of a geomagnetic storm and simultaneous plasma density measurements from the THEMIS spacecraft revealed that the decreasing frequencies were due to the refilling of the plasmasphere following the storm.

Queen Mary University London Press Release: School students identify sounds caused by solar storm.

AGU Geospace Blog: Sounds of a solar storm.

Citation: Archer, M. O., Hartinger, M. D., Redmon, R., Angelopoulos, V., Walsh, B. M., & Eltham Hill School Year 12 Physics students (2018). First results from sonification and exploratory citizen science of magnetospheric ULF waves: Long-lasting decreasing-frequency poloidal field line resonances following geomagnetic storms. Space Weather, 16.

August 21, 2018:

THEMIS ASI study of STEVE phenomenon featured in AGU News and Eos:

New Kind of Aurora is Not an Aurora at All

Thin ribbons of purple and white light that sometimes appear in the night sky were dubbed a new type of aurora when brought to scientists' attention in 2016. But new research suggests these mysterious streams of light are not an aurora at all but an entirely new celestial phenomenon.

Amateur photographers had captured the new phenomenon, called STEVE, on film for decades. But the scientific community only got wind of STEVE in 2016. When scientists first looked at images of STEVE, they realized the lights were slightly different than light from typical auroras but were not sure what underlying mechanism was causing them.

Alberta Aurora Chasers capture STEVE, the new-to-science upper atmospheric phenomenon, on the evening of April 10, 2018 in Prince George, British Columbia, Canada. Fellow Aurora Chaser Robert Downie kneels in the foreground while photographer Ryan Sault captures the narrow ribbon of white-purple hues overhead. The vibrant green aurora is seen in the distant north, located to the right in the photo. In this issue, Gallardo-Lacourt et al. use a ground based all-sky imager and in situ satellite data to study the origin of STEVE. Their results demonstrate that STEVE is different than aurora since the observation is characterized by the absence of particle precipitation. Credit: Ryan Sault.

Thin ribbons of purple and white light that sometimes appear in the night sky were dubbed a new type of aurora when brought to scientists' attention in 2016. But new research suggests these mysterious streams of light are not an aurora at all but an entirely new celestial phenomenon.

Amateur photographers had captured the new phenomenon, called STEVE, on film for decades. But the scientific community only got wind of STEVE in 2016. When scientists first looked at images of STEVE, they realized the lights were slightly different than light from typical auroras but were not sure what underlying mechanism was causing them.

In a new study, researchers analyzed a STEVE event in March 2008 to see whether it was produced in a similar manner as the aurora, which happens when showers of charged rain down into Earth's upper atmosphere. The study's results suggest STEVE is produced by a different atmospheric process than the aurora, making it an entirely new type of optical phenomenon.

"Our main conclusion is that STEVE is not an aurora," said Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union. "So right now, we know very little about it. And that's the cool thing, because this has been known by photographers for decades. But for the scientists, it's completely unknown."

The study authors have dubbed STEVE a kind of "skyglow," or glowing light in the night sky, that is distinct from the aurora. Studying STEVE can help scientists better understand the upper atmosphere and the processes generating light in the sky, according to the authors.

"This is really interesting because we haven't figured it out and when you get a new problem, it's always exciting," said Joe Borovsky, a space physicist at the Space Science Institute in Los Alamos, New Mexico who was not connected to the new study. "It's like you think you know everything and it turns out you don't."

Auroras are produced when electrons and protons from Earth's magnetosphere, the region around Earth dominated by its magnetic field, rain down into the ionosphere, a region of charged particles in the upper atmosphere. When these electrons and protons become excited, they emit light of varying colors, most often green, red and blue.

A group of amateur auroral photographers brought STEVE to scientists' attention in 2016. A Facebook ground called the Alberta Aurora Chasers had occasionally noticed bright, thin streams of white and purple light running east to west in the Canadian night sky when they photographed the aurora.

Auroras are visible every night if viewing conditions are right, but the thin light ribbons of STEVE were only visible a few times per year. The light from STEVE was also showing up closer to the equator than the aurora, which can only be seen at high latitudes.

The photographers first thought the light ribbons were created by excited protons, but protons can only be photographed with special equipment. The light protons produce falls out of the range of wavelengths picked up by normal cameras.

The aurora chasers dubbed the light ribbon occurrences "Steve," a reference to the 2006 film Over the Hedge. When researchers presented data about the unusual lights at a 2016 scientific conference, a fellow space physicist proposed converting the name into the backronym STEVE, which stands for Strong Thermal Emission Velocity Enhancement, and the researchers adopted it.

Scientists then started using data from satellites and images from ground-based observatories to try to understand what was causing the unusual light streaks. The first scientific study published on STEVE found a stream of fast-moving ions and super-hot electrons passing through the ionosphere right where STEVE was observed. The researchers suspected these particles were connected to STEVE somehow but were unsure whether they were responsible for producing it.

After that first study, of which Gallardo-Lacourt was a co-author, the researchers wanted to find out if STEVE's light is produced by particles raining down into the ionosphere, as typically happens with the aurora, or by some other process. In the new study, Gallardo-Lacourt and her colleagues analyzed a STEVE event that happened over eastern Canada on March 28, 2008, using images from ground-based cameras that record auroras over North America.

They coupled the images with data from NOAA's Polar Orbiting Environmental Satellite 17 (POES-17), which happened to pass directly over the ground-based cameras during the STEVE event. The satellite is equipped with an instrument that can measure charged particles precipitating into the ionosphere.

The study's results suggest STEVE is an entirely new phenomenon distinct from typical auroras. The POES-17 satellite detected no charged particles raining down to the ionosphere during the STEVE event, which means it is likely produced by an entirely different mechanism, according to the authors.

The researchers said STEVE is a new kind of optical phenomenon they call "skyglow." Their next step is to see whether the streams of fast ions and hot electrons in the ionosphere are creating STEVE's light, or if the light is produced higher up in the atmosphere.

Eos Research Spotlight: New Kind of Aurora Is not an Aurora at All, Eos. Published on 21 August 2018.

Citation: Gallardo-Lacourt, B., Liang, J., Nishimura, Y., & Donovan, E. (2018). On the origin of STEVE: Particle precipitation or ionospheric skyglow? Geophysical Research Letters, 45.

August 6, 2018:

THEMIS research profiles rapid fluctuations in Earth's surface geomagnetic field, Eos Highlight:

How Two Massive Space Storms Zapped Alaska

The 2015 St. Patrick's Day aurora seen in Donnelly Creek, Alaska. Credit: NASA/Sebastian Saarloos.

On St. Patrick's Day in 2015, people living as far south as Tennessee spotted brilliant green and red auroras glowing in the night skies. The northern lights—which are typically visible only at high latitudes—were caused by a space storm so intense it disrupted electrical fields on Earth's surface. Now, a new study helps to explain how space storms produce powerful, ground-level electric currents that disrupt power grids, gas and oil pipelines, and communication systems.

Scientists have long known that these currents, called geomagnetically induced currents (GICs), result from interactions between the fluctuating solar wind and Earth's magnetosphere, a region around the upper atmosphere dominated by the magnetic field that buffers our planet from space radiation. The ionosphere, a pulsating layer of charged particles that produces auroras, also plays an important role. Precisely how the storms produce the on-the-ground electric currents has been difficult to pinpoint, however.

To get a more detailed understanding, Ngwira et al. focused on two big space storms: the St. Patrick's Day event and a second space storm that occurred in March 2012. The team examined data from NASA's Time History of Events and Macroscale Interactions During Substorms mission, a suite of satellites that can sense the rapid release of energy just before auroras brighten and expand across the night sky. They also looked at ground monitoring data from several sites across Alaska, where the biggest GICs were detected during the storms.

The team found that the fastest, most intense fluctuations in the amplitude of Earth's magnetic fields occurred just as the auroras were spreading and brightening. The rapidly shifting magnetic fields pushed and pulled electrons at ground level, generating a powerful electric current. The findings support the hypothesis that the brief period leading up to an aurora, called a substorm, is the trigger for intense GICs. The finding could help scientists protect communication and energy systems from destructive electrical currents in the future. (Space Weather,, 2018)

Eos Research Spotlight: Underwood, E. (2018), How two massive space storms zapped Alaska, Eos, 99, Published on 06 August 2018.

Citation: Ngwira C. M., Sibeck, D., Silveira, M. D. V., Georgiou, M., Weygand, J. M., Nishimura, Y., & Hampton, D. (2018). A study of intense local dB/dt variations during two geomagnetic storms. Space Weather, 16, 676–693.

April 30, 2018:

THEMIS research on geosynchronous altitude magnetic field selected as Research Spotlight in Eos magazine:

How Space Storms Affect the Satellite Superhighway

Example of the magnetic field line tracing for the storm of 12–15 October 2016. The figure shows time evolution (colored from black to orange) of the magnetic field lines passing through the red cross, approximate position of geostationary satellite GOES-14. The lines in meridional and equatorial projections, respectively. (bottom) The SYM-Hindex variation during the storm (vertical bars indicate the time moments corresponding to the field lines of the same color in Figure 5 (top and middle).

Some 36,000 kilometers above Earth, over 400 commercial, telecommunication, and weather satellites dance in geosynchronous orbit, circling the planet at precisely the same rate that it turns. This so-called satellite superhighway is occasionally whipped by solar wind and fluctuating magnetic fields, a chaotic environment that can damage and interfere with the spacecraft. Now a new 3-D mathematical model of magnetic environment in the region could help researchers predict how storms affect the geosynchronous magnetic environment.

The researchers' last attempt to model the solar wind impact on the geosynchronous magnetic field was conducted more than 25 years ago and didn't account for space storms that occur when solar particles slam into Earth's protective magnetosphere. It also used data from only a single satellite, which limited the model's ability to capture the complex dynamics in this zone.

In their new study, Andreeva and Tsyganenko used radial basis functions—a numerical methodology to crunch data from multiple satellites, including Time History of Events and Macroscale Interactions during Substorms (THEMIS), Polar, Cluster, and the Van Allen Probes. This computational approach takes into account all major sources of the geomagnetic field, such as the ring and tail currents that result from the solar wind flow around Earth's magnetosphere.

Previously, the team had shown that this approach can accurately model the magnetic field in a given region, including its disturbance by space weather. In their new study, the researchers took into account both the current state of the solar wind and interplanetary magnetic field—the Sun's magnetic field that gets carried into space—and their previous history. They found that the radial basis function model performed better than earlier attempts to model the region and validated it using two separate data sets. Yet they were not able to fully model variations related to substorms, the violent and brief electromagnetic disturbances that cause auroras. The authors note this is a major stumbling block that will have to be addressed in future research.

Eos Research Spotlight: Underwood, E. (2018), How space storms affect the satellite superhighway, Eos, 99, Published on 30 April 2018.

Citation: Andreeva, V. A., and Tsyganenko, N. A. (2018). Empirical modeling of the quiet and storm time geosynchronous magnetic field. Space Weather, 16, 16–36.

April 11, 2018:

New book with THEMIS contributions selected as Editor's Highlight in Eos magazine (continued from home page):

Electric Currents in Outer Space Run the Show

Modern society relies on electric currents. We can generate them, guide them from one place to another (including very remote places), and make them work for us. The use of electricity has provided the greatest technological advances in humankind. But electric currents also occur in nature by themselves and "run the show" in outer space. Electric Currents in Geospace and Beyond, a new book just published by the American Geophysical Union, explores our most up-to-date understanding of electric currents in the solar system. Here the editors answer some questions about past and recent advances in this field.

How are these currents observed and measured?

Since electric currents are comprised of moving charged particles, such as ions and electrons, the most direct way to measure currents is by probing and counting the individual particles. Highly tuned instruments that fly on board satellites do exactly that. While particle counting is quite challenging, as one might expect, one can also make use of the fact that electric currents generate a magnetic field around them, which in turn can be measured, more easily, by instruments, called magnetometers. From these magnetic fields one can then infer using Maxwell's equations the underlying currents.

In fact, this remote sensing allows us to infer some electric currents in outer space from ground-based magnetometers. However, a difficulty is to separate the field contributions at the same location from several distant currents that are simultaneously present.

In the case of electric currents on the Sun, neither the charged particles nor the magnetic field can be measured directly, so yet another method is used, which relies on the signature that the magnetic field leaves on light from the Sun (due to the Zeeman effect). This allows the magnetic field to be inferred, and then the electric current.

How is the book organized?

A remarkable result of space research is that there are several common current systems (ring currents, current sheets, field-aligned currents, ionospheric currents) that occur at several planets in spite of their great differences, such as physical dimension, planetary rotation rate, ionospheric conductivity, and exposed solar wind conditions. However, along with these current systems goes a large variety of different aspects of each current system. Therefore, we decided to organize the 30 chapters in the book by these common current systems (as separate sections), allowing direct comparisons among different astronomical bodies, which also includes the Sun, moons and comets. This aligns with the ever-growing interdisciplinary approach to space physics.

What have been some of the recent research advances in this field?

Multi-spacecraft missions in the near-Earth space launched in the past 20 years (e.g., Cluster, THEMIS, MMS, Swarm, or the AMPERE experiment using Iridium satellites), together with comprehensive networks of ground instruments (e.g., SuperMag, SuperDARN, MIRACLE, THEMIS), made it possible to advance the understanding of the electric current systems in the magnetosphere and ionosphere – like those associated with substorms and, on smaller scales, with bursts of fast magnetospheric plasma flows, the cusp current system, the multi-scale structure of the field-aligned currents, or the three-dimensional configuration of the ionospheric currents.

The new technique of energetic neutral atoms enabled global imaging of the ring current around the Earth (by the IMAGE mission), including storm time development, and Saturn (by the Cassini mission), while missions like ARTEMIS and Rosetta provided detailed perspectives on the currents around the Moon and in cometary comae, respectively.

In solar physics, the advent of instruments in space to infer electric currents at the surface of the Sun (on the Hinode and Solar Dynamics Observatory satellites) has resulted in measurements of unprecedented quality and resolution, leading to many new research results.

Eos Editor's Highlight: Keiling, A., O. Marghitu, and M. Wheatland (2018), Electric currents in outer space run the show, Eos, 99, Published on 11 April 2018.

Citation: Keiling, A., O. Marghitu, and M. Wheatland, Eds. (2018), Electric Currents in Geospace and Beyond, American Geophysical Union, 568 pages.

March 28, 2018:

TWINS research using THEMIS data selected as Editor's Highlight in Eos magazine (continued from home page):

The Big Picture in Geospace

In 2008, the NASA mission called TWINS, or Two Wide-angle Imaging Neutral-atom Spectrometers, began obtaining the first stereo images of the near-Earth region of space. An article recently published in Reviews of Geophysics reviews the last several years of science results from TWINS and multi-mission observations within the Heliophysics System Observatory (HSO), including THEMIS. The editors asked the authors to explain what the instruments have been measuring, and describe some of the most interesting findings.

Two major constituents of geospace are imaged by TWINS. The ring current is composed of energetic ions and electrons trapped by the Earth's magnetic field. The neutral hydrogen (H) exosphere is made of colder atoms bound by gravity. Credit: Adapted from Goldstein and McComas, 2018

What and where is "geospace"?

Geospace is the region of space close to the Earth and dominated by the Earth's own magnetic field. This region contains a variety of neutral gases and plasmas (ionized gases) which are the major players in geomagnetic storms—disturbances in near-Earth space that strike our magnetic field, and that can disrupt our technology.

Our review article considers two constituents of geospace. The first is the ring current, which is made of energetic ions and electrons that are trapped by Earth's magnetic field. During geomagnetic storms, the ring current's magnetic field is strong enough to measure on the ground with an ordinary refrigerator magnet. The second is the exosphere, which is made of neutral hydrogen atoms. The hydrogen exosphere helps control the duration and strength of geomagnetic storms by neutralizing the ions of the ring current.

What information about geospace has NASA's TWINS mission been collecting?

NASA's TWINS mission has used two separate spacecraft to perform stereo imaging of the ring current and the exosphere. Each TWINS spacecraft carries two specialized cameras. The first is an energetic neutral atom (ENA) camera. This measures the particles emitted when the exosphere neutralizes the ions of the ring current. The second is a camera that measures the ultraviolet glow of the hydrogen atom exosphere—called the "geocorona." Using these cameras TWINS observes the big picture, that is, the large-scale (global) response to storms—just as a weather satellite can show the progress of a hurricane. Since 2008, the two TWINS observatories have recorded the global response to over 200 storms ranging from mild to major.

What have been some of the most significant or surprising scientific findings from TWINS?

Geospace has been imaged before but TWINS was the first mission to perform stereo imaging—with cameras on two separate spacecraft—of the ring current and exosphere. This stereo imaging has revealed extra dimensionality and structure that was previously undetected by monoscopic imaging. In particular, for the geomagnetic storm around St. Patrick's Day 2015, THEMIS conjuctions were critical in measuring the dynamic location and motion of the magnetopause and plasmapause in response to the solar wind. THEMIS in-situ observations in tandem with TWINS' imaging has allowed monitoring of storms from start to finish, providing a validated global view of the ring current and establishing its asymmetric nature during storms and symmetry during the recovery phase. The global view afforded by THEMIS probes ground based observatories in addition to multiple probes in the HSO has revealed a surprising amount of time variability and structure in the exosphere and magnetosphere.

Eos Editor's Highlight: Goldstein, J. (2018), The big picture in geospace, Eos, 99, Published on 28 March 2018.

Citation: Goldstein, J., and McComas, D. J. (2018). The big picture: Imaging of the global geospace environment by the TWINS mission. Reviews of Geophysics, 56, 251–277.

March 21, 2018:

THEMIS findings on EMIC waves selected as JGR Editor's Highlight:

In their paper, Kim et al. show a clear connection between a phenomenon at the edge of geospace (the magnetopause) and something deep within the inner magnetosphere that normally isn't associated with that other process. Specifically, the authors observed a twisted magnetic field line structure, called a traveling convection vortex, and the generation of a particular plasma wave. They attribute the cause of both features to be a solar wind pressure pulse.

Magnetic field data obtained by (top) THEMIS A, (middle) THEMIS D, and (bottom) THEMIS E during the events presented in this study. The horizontalcolor bars below each panel denote the regions where each spacecraft was situated. The two grey boxes indicate the time periods of the EMIC wave events. Credit: NJIT

JGR Editor's Highlight

Citation: Kim, H., et al. (2017), Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events, J. Geophys. Res. Space Physics, 122, 7336–7352, doi:10.1002/2017JA024108.

February 14, 2018:

THEMIS and ERG findings on pulsating aurora published in Nature, selected as Editor's Choice top news item for 2018:

Sometimes on a dark night near the poles, the sky pulses a diffuse glow of green, purple, and red. Unlike the long, shimmering veils of typical auroral displays, these pulsating auroras are much dimmer and less common. While scientists have long known auroras to be associated with solar activity, the precise mechanism of pulsating auroras was unknown. Now, new research, using data from NASA's THEMIS mission and Japan's ERG (also known as Arase) satellite, has finally captured the missing link thought responsible for these auroras. Their findings are published in the Feb. 14th issue of the journal Nature.

Artist rendition of the ERG satellite in the magnetosphere (dark blue), with electrons (aqua) spiraling along magnetic field lines (light blue). Credit: JAXA

Earth's magnetic bubble — the magnetosphere — protects the planet from high-energy radiation coming from the Sun and interstellar space, but during particularly strong solar events, particles can slip through. Once inside, some particles become entrapped along Earth's magnetic field lines, bouncing between poles. Here, they can encounter a type of plasma wave, known as whistler mode chorus, created by fluctuating electric and magnetic fields. The waves have characteristic rising tones — reminiscent of the sounds of chirping birds — and are able to efficiently accelerate electrons. Ultimately, they scatter some of the electrons into Earth's upper atmosphere where they glow upon colliding with particles there, creating auroras.

Figure (a), The open blue arrow represents northward-streaming electrons with an empty loss cone (b) before chorus waves interact with them (c). The blue filled arrows represent the same electrons but with a filled loss cone (d) after their interaction with chorus waves (pitch-angle scattering by waves). The red arrows represent loss-cone-filling electrons streaming southwards. The spacecraft location is denoted by a black filled circle. b–d, The evolution of the electron PAD. Because chorus activity is intermittent, loss cone filling and depletion are repeated, causing auroral pulsations. Credit: Kasahara et al.

While scientists have long believed this mechanism to be responsible for pulsating auroras, they had no definitive proof until now. The multipoint observations from the ERG satellite and ground-based all-sky cameras from the THEMIS mission allowed scientists to pinpoint the cause and effect, seeing the event from start to end.

Research done by NASA's ground-based camera and Japan's spacecraft in the unique near-Earth laboratory has applications further afield. Chorus waves have been observed around other planets in the solar system, including Jupiter and Saturn. Likely, the processes observed around Earth can explain auroras on these gas giants as well as on planets around other stars. The results also help scientists better understand how plasma waves, which occur across the universe, can influence electrons.

This paper was also selected by Nature as an Editor's Choice top news item for 2018, congratulations to Kasahara, et al., for this outstanding achievement!

Nature News Release:

Citation: Kasahara, S., Y. Miyoshi, S. Yokota, T. Mitani, Y. Kasahara, S. Matsuda, A. Kumamoto, A. Matsuoka, Y. Kazama, H. U. Frey, V. Angelopoulos, S. Kurita, K. Keika, K. Seki & I. Shinohara (2018), Pulsating aurora from electron scattering by chorus waves, Nature, 554, 337–340, doi:10.1038/nature25505.

January 28, 2018:

ESA News features CLUSTER-THEMIS study measuring turbulence in Earth's magnetosheath:

For the first time, scientists have estimated how much energy is transferred from large to small scales within the magnetosheath, the boundary region between the solar wind and the magnetic bubble that protects our planet. Based on data collected by ESA's Cluster and NASA's THEMIS missions over several years, the study revealed that turbulence is the key, making this process a hundred times more efficient than in the solar wind.

The planets in the Solar System, including our Earth, are bathed in the solar wind, a supersonic flow of highly energetic, charged particles relentlessly released by the Sun. Our planet and a few others stand out in this all-pervasive stream of particles: these are the planets that have a magnetic field of their own, and so represent an obstacle to the sweeping power of the solar wind. It is the interaction between Earth's magnetic field and the solar wind that creates the intricate structure of the magnetosphere, a protective bubble that shields our planet from the vast majority of solar wind particles. So far, scientists have achieved a fairly good understanding of the physical processes that take place in the solar wind plasma and in the magnetosphere. However, many important aspects are still missing regarding the interplay between these two environments and about the highly turbulent region that separates them, known as magnetosheath, where it is suspected that most of the interesting action happens.

ESA's Cluster mission (top) and NASA's THEMIS mission (bottom) flying through Earth's magnetosheath, the highly turbulent boundary region between the solar wind and the magnetosphere around our planet. A study based on data collected by these missions has estimated how much energy is transferred from larger to smaller scales within the magnetosheath, revealing that turbulence is the key, making this process a hundred times more efficient than in the solar wind.

"To learn how energy is transferred from the solar wind to the magnetosphere, we need to understand what goes on in the magnetosheath, the 'grey area' between them," says Lina Zafer Hadid, from the Swedish Institute of Space Physics in Uppsala, Sweden. Lina is the lead author of a new study that quantifies, for the first time, the role of turbulence in the magnetosheath. The results are published today in Physical Review Letters. "In the solar wind, we know that turbulence contributes to the dissipation of energy from large scales of hundreds of thousands of kilometres to smaller scales of a kilometre, where plasma particles are heated up and accelerated to higher energies," explains co-author Fouad Sahraoui from the Laboratory of Plasma Physics in France. "We suspected that a similar mechanism must be at play in the magnetosheath too, but we could never test it until now," he adds.

The magnetosheath plasma is more turbulent, home to a greater extent of density fluctuations and can be compressed to a much higher degree than the solar wind. As such, it is substantially more complex, and scientists have only in recent years developed the theoretical framework to study the physical processes taking place in such an environment. Lina, Fouad and their collaborators combed through a vast volume of data collected between 2007 and 2011 by the four spacecraft of ESA's Cluster and two of the five spacecraft of NASA's THEMIS missions, which fly in formation through Earth's magnetic environment. When they applied the recently developed theoretical tools to their data sample, they were in for a big surprise. "We found that density and magnetic fluctuations caused by turbulence within the magnetosheath amplify the rate at which energy cascades from large to small scales by at least a hundred times with respect to what is observed in the solar wind," explains Lina.

The new study indicates that about 10-13 J of energy is transferred per cubic metre every second in this region of Earth's magnetic environment. "We expected that compressible turbulence would have an impact on the energy transfer in magnetosheath plasma, but not that it would be so significant," she adds. In addition, the scientists were able to derive an empirical correlation that links the rate at which energy is dissipated in the magnetosheath with the fourth power of another quantity used to study the motion of fluids, the so-called turbulent Mach number. Named after Austrian physicist Ernst Mach, it quantifies the speed of fluctuations in a flow with respect to the speed of sound in that fluid, indicating whether a flow is subsonic or supersonic.

While the energy transfer rate is tricky to determine unless using space probes that take in situ measurements, like the Cluster spacecraft sampling the plasma around Earth, the Mach number can be more easily estimated using remote observations of a variety of astrophysical plasma beyond the realm of our planet. "If this empirical relation turns out to be universal, it will be extremely useful to explore cosmic plasma that cannot be directly probed with spacecraft, such as the interstellar medium that pervades our Milky Way and other galaxies," says Fouad.

The scientists are looking forward to comparing their results with measurements of the plasma surrounding other Solar System planets with an intrinsic magnetic field, for example using NASA's Juno mission, currently at Jupiter, and ESA's future Jupiter Icy Moons Explorer, and also the joint ESA-JAXA BepiColombo mission to Mercury that is scheduled for launch later this year. "It is very exciting that a study based on several years of Cluster data has found the key to address a major, long unsolved question in plasma physics," says Philippe Escoubet, Cluster Project Scientist at ESA.

Citation: L.Z. Hadid, F. Sahraoui, S. Galtier, and S.Y. Huang (2018), Compressible Magnetohydrodynamic Turbulence in the Earth's Magnetosheath: Estimation of the Energy Cascade Rate Using in situ Spacecraft Data, Phys. Rev. Lett. 120, 055102, doi:10.1103/PhysRevLett.120.055102.

September 25, 2017:

THEMIS publications selected as JGR Editor's Highlights:

Congrats to Prof. Katariina Nykyri and colleagues for her recent AGU highlighted paper which used Kelvin-Helmholtz simulations, motivated by THEMIS observations. The study finds that small fluctuations in the solar wind as it streams toward the Earth's magnetic shield can affect the speed and strength of these KH waves. The KH waves grow faster and stronger when solar wind fluctuations are stronger, under otherwise similar average conditions.

Comparison of the KHI dynamics for periodic (1A and 1B) and open (1C) boundary conditions. The 1B and 1C show the high-resolution cases. Background color is the plasma density, black lines are magnetic field, and white arrows are plasma velocity vectors. When large-amplitude, low-frequency seed velocity fluctuations exist in the magnetosheath, the resulting KH waves grow faster, get larger in size, and can transport more plasma through magnetic boundary.

JGR Editor's Highlight

AGU GeoSpace Blog

Citation: Nykyri, K., X. Ma, A. Dimmock, C. Foullon, A. Otto, and A. Osmane (2017), Influence of velocity fluctuations on the Kelvin-Helmholtz instability and its associated mass transport, J. Geophys. Res. Space Physics, 122, doi:10.1002/2017JA024374.

Congrats to Dr. Naoko Takahashi et al. on their Heliophysics System Observatory studies of storm sudden commencements. Using THEMIS and allied measurements from the HSO to study the relative importance of two wave modes, they found that fast and shear Alfvén modes change as the disturbance moves earthwards. The latter is relatively more important closer to the Earth. This gives new insight into solar wind-magnetosphere-ionosphere interactions.

Time evolution of spatial distribution of the calculated Ey in the equatorial plane. The positive value (red color) is duskward. "T" above each panel indicates the difference from the given onset of sudden commencements.

JGR Editor's Highlight

Citation: Takahashi, N., Y. Kasaba, Y. Nishimura, A. Shinbori, T. Kikuchi, T. Hori, Y. Ebihara, and N. Nishitani (2017), Propagation and evolution of electric fields associated with solar wind pressure pulses based on spacecraft and ground-based observations, J. Geophys. Res. Space Physics, 122, 8446–8461, doi:10.1002/2017JA023990.

Congrats to Dr. San Lu and colleagues for their feature paper in JGR-Space Physics. Their study uses hybrid simulations and simultaneous THEMIS, Geotail and ARTEMIS observations in the magnetotail to show that under slow convection the robust vertical temperature gradient (normal to the tail current sheet) matches and can be used to investigate the tailward temperature gradient as function of distance from the Earth. The results suggest that theoretical models of tail equilibrium must be improved in order to incorporate this significant and robust temperature gradient.

THEMIS Nugget Summary

Citation: Lu, S., A. V. Artemyev, V. Angelopoulos, Y. Lin, and X. Y. Wang (2017), The ion temperature gradient: An intrinsic property of Earth's magnetotail, J. Geophys. Res. Space Physics, 122, doi:10.1002/2017JA024209.

July 25, 2017:

THEMIS/ARTEMIS researcher awarded AGU Medal:

Wen Li (Boston University and UCLA) was recently awarded the 2017 AGU Macelwane Medal. Wen's work on whistler mode chorus and other inner magnetosphere instabilities using predominantly THEMIS data between 2007 and 2014, and more recently adding Van Allen Probes and Juno data to her studies, has made significant contributions to wave particle interactions in planetary magnetospheres. Congratulations Wen!

James B. Macelwane Medal

The James B. Macelwane Medal is given annually to three or up to five honorees in recognition for "significant contributions to the geophysical sciences by an outstanding early career scientist." Established in 1961, the Macelwane Medal was renamed in 1986 in honor of former AGU president James B. Macelwane (1953–1956). Renowned for his contributions to geophysics, Macelwane was deeply interested in teaching and encouraging young scientists.

AGU Medal Recipients Press Release

About the James B. Macelwane Medal

July 11, 2017:

THEMIS research chosen as JGR Editor's Highlight:

The paper by Terry Liu et al. "Statistical study of particle acceleration in the core of foreshock transients," was selected as an Editor's Highlight in JGR. Particle energization is a key process in space plasmas. This paper presents a statistical study of ion and electron energization in the core of foreshock transients, showing that the energization of ions and electrons are different. It also shows that the ion and election energization are positively correlated with the solar wind speed. Way to go Terry!

Computer simulation of Earth's magnetosphere foreshock region, showing the formation of spontaneous hot flow anomalies (SHFAs). X1 and X2 represent hypothetical spacecraft. Credit: N. Omidi, Solana Scientific, 2016.

JGR Highlight

Source: Liu, T. Z., V. Angelopoulos, H. Hietala, and L. B. Wilson III (2017), Statistical study of particle acceleration in the core of foreshock transients, J. Geophys. Res. Space Physics, 122, doi:10.1002/2017JA024043.

Omidi, N., J. Berchem, D. Sibeck, and H. Zhang (2016), Impacts of spontaneous hot flow anomalies on the magnetosheath and magnetopause, J. Geophys. Res. Space Physics, 121, 3155–3169, doi:10.1002/2015JA022170.

June 30, 2017:

Study using THEMIS on front cover of GRL:

Chosen as the June cover of Geophysical Research Letters, a paper by Zhao et al. investigated properties of hot flow anomalies (HFA), which generated ultra-low frequency (ULF) waves observed by multiple spacecraft and ground based observatories. Nearly monochromatic Pc3 ULF standing Alfvén waves generated by an HFA were observed by THEMIS, GOES spacecraft and ground stations. The Pc3 ULF waves were observed at dawn, noon, and dusk sectors, as well as the nightside, indicating that the Pc3 ULF wave response of the magnetosphere to the HFA is global. These results show that the impact of HFAs to the magnetosphere is much stronger than what we thought before.

Link: Zhao, L. L., H. Zhang, and Q. G. Zong (2017), Global ULF waves generated by a hot flow anomaly, Geophys. Res. Lett., 44, 5283–5291, doi:10.1002/2017GL073249.

June 16, 2017:

THEMIS auroral researchers highlighted in Scientia Magazine:

Space physicists Dr Yukitoshi (Toshi) Nishimura and Dr Ying Zou, along with their colleagues at Boston University and at UCLA, study the interactions between Earth's atmosphere and energy that flows from the solar wind to determine how the Northern Lights – and the Southern Lights – get their beauty.

Especially at night from earliest childhood, most of us have been struck by the wonders of Nature that surround us. The blue seas, the verdant forests, the colourful birds and fascinating animals – all of these have at one time or another awed us with their beauty and fascination. But one special sight that has drawn human attention from the dawn of history is the twinkling, always moving but somehow unchanging, night sky. The stars, the planets, the romance of the Universe – it appears to be moving around us just outside our reach. It was this very sight that inspired Dr. Toshi Nishimura to make space physics his life's work. "I was a kid who liked to watch stars and think about undiscovered worlds in the universe," he tells Scientia. "One day my parents bought me a small telescope and I was excited by watching Saturn's rings, the Jovian satellites, lunar craters and comets." This became his passion. So when Dr. Nishimura went to college, he took lectures of space science and electromagnetism, and soaked up his professors' enthusiasm about space. That energy simply whet his curiosity even more, so he decided to study the science of space.

But there is one particular phenomenon of the night sky, one that people in many parts of the world never see, that is perhaps the most stunning of all the night's visions – the auroras, those hypnotic shows of dancing lights that fill the skies, especially near or after dark in the higher latitudes. In the northern hemisphere, it is called the aurora borealis or Northern Lights, while south of the equator, it is the aurora australis or Southern Lights. Often highlighted in movies and television programmes set in extreme northern locations, auroras are usually depicted as pale green or pink. However, auroras have been seen in shades of red, yellow, green, blue, and violet.

Link: Berg, N., et al. (2017), Studying The Auroras And What Makes Them Shine, Scientia 113, June 2017.

January 31, 2017:

THEMIS results highlighted in journal Physics of Plasmas:

Physics of Plasmas editors selected the article "Ion motion in a polarized current sheet" as a SCILIGHT summary. Congrats to first author and UCLA undergraduate student Ethan Tsai for his first publication!

Constantly buffeted by the solar wind, Earth's magnetosphere captures and explosively releases some of that solar energy as particle heat and space electrical currents, threatening astronauts, satellites, and the electrical grid. Key to understanding our dynamic magnetosphere is the study of its flowing plasmas, or charged particles, and their electromagnetic fields.

Cartoon depiction of the Earth's magnetosphere, with the current sheet region on the right and the domain of enhanced electron/suppressed ion currents. Credit: E. Masongsong/A.V. Artemyev, UCLA EPSS

Particle behavior within the equatorial current sheet, a thin but dynamic plasma layer found in planetary magnetospheres, is poorly understood despite its importance in accelerating particles and sourcing intense currents during solar storms. Theory suggests that positively-charged ions in thin current sheets should produce a strong diamagnetic current density, yet this does not always fit observations. Researchers at UCLA explain this discrepancy in the January 2017 issue of Physics of Plasmas. They found that the decoupling of ion and electron motions can, at times, generate a new electric field that significantly alters current sheet structure and charged particle motions, effectively reducing the current density. In addition, previously under-appreciated "transient" ions actually play a significant role in regulating the net current. These findings show that modeled electric fields of typical magnitude can influence transient ion motion and modify the net current from being ion-dominated to electron-dominated quite rapidly. Using THEMIS spacecraft measurements, the researchers showed that this model corroborates with observations in Earth's magnetosphere. This new theoretical analysis will improve our plasma models and help scientists understand the physics of planetary and laboratory current sheets.

Citation: Tsai, E., A.V. Artemyev, V. Angelopoulos (2017), Ion motion in a polarized current sheet, Physics of Plasmas, 24, 012908, doi:10.1063/1.4975017.

November 14, 2016:

NASA News and Eos present THEMIS findings of unusual origins of high-energy electrons:

Congratulations to Wilson et al. for their paper "Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock," selected as an Editor's Highlight in the journal Physical Review Letters. They describe the novel acceleration of electrons in the ion foreshock, which can inform our understanding of other collisionless shock processes such as coronal mass ejections and supernovae. Using observations from NASA's THEMIS mission, they show that the turbulent ion foreshock region can accelerate electrons up to speeds approaching the speed of light. Such extremely fast particles have been observed in near-Earth space and many other places in the universe, but the mechanisms that accelerate them have not yet been concretely understood.

The research finds electrons can be accelerated to extremely high speeds in a near-Earth region farther from Earth than previously thought possible – leading to new inquiries about what causes the acceleration. These findings may change the accepted theories on how electrons can be accelerated not only in shocks near Earth, but also throughout the universe. Having a better understanding of how particles are energized will help scientists and engineers better equip spacecraft and astronauts to deal with these particles, which can cause equipment to malfunction and affect space travelers.

An artist's rendering (not to scale) of the electron energization process, with spiralling electrons in yellow, the interplanetary magnetic field lines in light blue, the ion foreshock in orange, the bowshock in red, and magnetosphere in teal. Credit: E. Masongsong/UCLA EPSS/NASA

"This affects pretty much every field that deals with high-energy particles, from studies of cosmic rays to solar flares and coronal mass ejections, which have the potential to damage satellites and affect astronauts on expeditions to Mars," said Lynn Wilson, lead author of the paper on these results at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The results, published in Physical Review Letters, on Nov. 14, 2016, describe how such particles may get accelerated in specific regions just beyond Earth's magnetic field and can gain energy through electromagnetic activity in the foreshock region itself.

This image represents one of the traditional proposed mechanisms for accelerating particles across a shock, called a shock drift acceleration. The electrons (yellow) and protons (blue) can be seen moving in the collision area where two hot plasma bubbles collide (red vertical line). The cyan arrows represent the magnetic field and the light green arrows, the electric field. Credits: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

The THEMIS spacecraft found electrons accelerated to extremely high energies which lasted less than a minute, but were much higher than the average energy of particles in the region, and much higher than can be explained by collisions alone. Simultaneous observations from the additional Heliophysics spacecraft, Wind and STEREO, showed no solar radio bursts or interplanetary shocks, so the high-energy electrons did not originate from solar activity.

"This is a puzzling case because we're seeing energetic electrons where we don't think they should be, and no model fits them," said David Sibeck, co-author and THEMIS project scientist at NASA Goddard. "There is a gap in our knowledge, something basic is missing."

The electrons also could not have originated from the bow shock, as had been previously thought. If the electrons were accelerated in the bow shock, they would have a preferred movement direction and location – in line with the magnetic field and moving away from the bow shock in a small, specific region. However, the observed electrons were moving in all directions, not just along magnetic field lines. Additionally, the bow shock can only produce energies at roughly one tenth of the observed electrons' energies. Instead, the cause of the electrons' acceleration was found to be within the foreshock region itself.

This visualization represents one of the traditional proposed mechanisms for accelerating particles across a shock, called a shock drift acceleration. The electrons (yellow) and protons (blue) can be seen moving in the collision area where two hot plasma bubbles collide (red vertical line). The cyan arrows represent the magnetic field and the light green arrows, the electric field. Credits: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

"It seems to suggest that incredibly small scale things are doing this because the large scale stuff can't explain it," Wilson said. High-energy particles have been observed in the foreshock region for more than 50 years, but until now, no one had seen the high-energy electrons originate from within the foreshock region. This is partially due to the short timescale on which the electrons are accelerated, as previous observations had averaged over several minutes, which may have hidden any event. THEMIS gathers observations much more quickly, making it uniquely able to see the particles. Next, the researchers intend to gather more observations from THEMIS to determine the specific mechanism behind the electrons' acceleration.

For more specific details, please refer to the THEMIS Science Nugget Summary here.

NASA Press Release:
Johnson-Groh, Mara. "NASA Finds Unusual Origins of High-Energy Electrons"

Wilson III, L.B., D.G. Sibeck, D.L. Turner, A. Osmane, D. Caprioli, and V. Angelopoulos (2016), Relativistic electrons produced by foreshock disturbances observed upstream of the Earth's bow shock,Phys. Rev. Lett. Vol. 117(21), doi:10.1103/PhysRevLett.117.215101.

September 12, 2016:

THEMIS sees auroras dance to the rhythm of the magnetosphere:

Using the THEMIS probes, ground magnetometers and all-sky cameras, Panov et al. describe the link between an oscillating magnetic field line in the magnetotail and a discrete patch of brightening aurora, published in the journal Nature Physics.

The majestic aurora has captivated humans for millennia, yet the mysterious lights' electromagnetic nature and connection to solar activity were only realized in the last 150 years. Detailed study of the aurora has finally become possible in recent decades with coordinated multi-satellite observations, and worldwide networks of ground-based magnetic sensors and cameras. Using data from NASA's THEMIS mission, an international team of scientists observed Earth's vibrating magnetic field at an altitude of 40,000 miles, more than 5 times the Earth's diameter, while simultaneously capturing the northern lights dancing in the night sky over Canada. Their findings, reported in the journal Nature Physics, are the first to directly map the back-and-forth motion of this distant magnetic field and the resulting electrical currents to a particular region of brightening aurora in Earth's upper atmosphere. This is an important link in understanding and eventually predicting how solar activity and space electricity can impact our technological infrastructure.

An artist's rendering (not to scale) of a cross-section of the magnetosphere, with the solar wind on the left in yellow and magnetic field lines emanating from the Earth in blue. The five THEMIS probes were well-positioned to directly observe one particular magnetic field line as it oscillated back and forth roughly every six minutes. In this unstable environment, electrons in near-Earth space, depicted as white dots, stream rapidly down magnetic field lines towards Earth's poles. There, they interact with oxygen and nitrogen particles in the upper atmosphere, releasing photons and brightening a specific region of the aurora. Credits: Emmanuel Masongsong/UCLA EPSS/NASA

The Earth is connected to the sun via the solar wind, an outward flow of electromagnetic radiation and charged particles (plasma) that affects all the planets, moons, comets, and asteroids in our solar system. These interactions, collectively known as space weather, include solar flares and violent plasma eruptions that could jam radio signals, damage weather, communications and GPS satellites, or even disable our global electrical power grid. Luckily for us, Earth has a spinning, molten metal core that generates a magnetic force field known as the magnetosphere. Magnetic field lines, like immense loops that extend outward from the Earth's north and south poles, form a giant protective bubble that shields us from most harmful space weather.

Under the right conditions, however, some solar wind particles and energy can enter the magnetosphere and subsequently be released in powerful bursts that can power the auroras, called a substorm. The magnetic field lines surrounding our planet vibrate wildly and mobilize the surrounding plasma, causing electrons to stream along the magnetic field lines until they fall into Earth's poles. The electrons collide with atmospheric oxygen and nitrogen atoms, which then emit the familiar green and red/blue colors of the aurora. This process is like a cosmic electric guitar string, whose motion is converted to an electrical current that flows into a distant amplified speaker, but instead of a note it results in an epic plasma light show!

Animation of a substorm and the flow of electrons along magnetic field lines that powers the auroras. Credit: NASA

In 2007 NASA launched THEMIS's five satellites to make coordinated measurements of space plasmas and ground auroras, in order to understand this energy release. In the study reported in Nature Physics, the space and ground assets were particularly well-positioned to capture the motion of the oscillating magnetic field lines together with the aurora they produced. The oscillation frequency was a mere one cycle every six minutes, yet the field line stretched back and forth by as much as two Earth diameters and the power produced, about 10GW, dwarfed the generating capacity of the largest nuclear power plants. Ground-based magnetic sensors across Canada and Greenland recorded the inflowing electrical currents, while specialized all-sky cameras captured the aurora as it brightened and dimmed, appearing to dance in lock-step with the six minute period of the vibrating magnetic field line. To verify this correlation, the researchers compared the electromagnetic energy released deep in the magnetosphere with the amount dissipated in the Earth's upper atmosphere. "We were delighted to see such a strong match," said Evgeny Panov, lead author and researcher at the Space Research Institute, of the Austrian Academy of Sciences in Graz. "These observations reveal the missing link in the conversion of magnetic energy to particle energy that powers the aurora."

Top right: animated computer model of the magnetic field line oscillating once every six minutes, streaming electrons Earthward with every contraction. Bottom right: actual spacecraft data plot showing auroral brightness, electric current over time, and magnetic field line distance from Earth. Bottom left: ionospheric electric current map showing inflowing (red) and outflowing (blue) electrons, derived from ground magnetometer observations. Top left: all-sky camera composite video showing auroral brightening, coinciding with inward magnetic field motion and electron influx into the ionosphere every six minutes. The five colored crosses represent the THEMIS probe positions with respect to the magnetic field line's origin in the magnetosphere. Credit: E. Panov, IWF Graz.

The most intense geomagnetic storm on record occurred in 1859 when space weather phenomena affected few people, whereas today a broad range of industries and infrastructure would be crippled by such a space storm. With the continued growth of the commercial space industry, space tourism, and increasing dependence on GPS positioning for automated cars and aircraft, accurate space weather forecasting and alerts are becoming ever more crucial. THEMIS is a key component of this research fleet, refining our ability to make higher-fidelity space weather models. "Even after nearly ten years, the probes are still in great health, and our growing network of magnetometers and all-sky cameras continue to generate high quality data," said Vassilis Angelopoulos, co-author and THEMIS principal investigator at UCLA.

NASA Press Release:
Tran, Lina. "NASA's THEMIS Sees Auroras Move to the Rhythm of Earth's Magnetic Field"

E. V. Panov, W. Baumjohann, R. A. Wolf, R. Nakamura, V. Angelopoulos, J. M. Weygand, M. V. Kubyshkina. Magnetotail energy dissipation during an auroral substorm. Nature Physics, 2016; DOI: 10.1038/nphys3879

July 29, 2016:

THEMIS observations of dipolarization fronts selected as AGU Research Spotlight:

THEMIS explains the origin of a new electrical current system in Earth's tail. The interaction between the solar wind and the Earth's magnetic field draws out the Earth's magnetosphere into a long, tapered "magnetotail." Within the magnetotail, intense magnetic fields emanating from magnetic reconnection move towards Earth and accelerate ambient charged particles in their path, converting magnetic energy to particle energy. Using observations from NASA's THEMIS spacecraft, researchers found that these interactions produce a characteristic decrease in the magnetic field in the area just preceding the moving front. These pockets of low magnetic field are important as they create conditions for particle trapping and further acceleration.

A long and thin current sheet (white dotted line) is embedded at the equatorial plane of in the magnetotail. A DF (red dashed line) is characterized by a sudden increase of northward magnetic field which propagates towards the Earth (red arrow). The DF is detected by three THEMIS spacecraft whose observations show a current density reduction ahead of the DF. Computer simulations found that the current density reduction is due to the generation of an electrostatic field (shown by the color coded region ahead of the DF, orange means the electric field's direction is towards north and blue means south) originating from the ion reflection by the DF. Note that the structures' spatial scale is enlarged for a better illustration. Image Credit: Emmanuel Masongsong, UCLA.

To understand why they arise, the researchers simulated the scenario with a computer model that follows the particles and their electromagnetic fields self-consistently. They found that ambient ions are reflected by the reconnected magnetic field's passage but the lighter electrons stay behind. This ion-electron separation generates a small electrostatic field which drives a new current system, ahead of and opposite the reconnected magnetic field. This new current system results in the pockets of decreased magnetic field. Both currents and fields were observed consistent with the simulation in the THEMIS data. This understanding resolves how some of the most complex interactions within Earth's magnetosphere occur, helping us track how energy is transferred from the solar wind to Earth's environment.

For more specific details, please refer to the THEMIS Science Nugget Summary here.

AGU Research Spotlight:
Yan, W. (2016), Mysteries of the magnetosphere, Eos, 97, doi:10.1029/2016EO055715.

Lu, S., A. V. Artemyev, V. Angelopoulos, Q. Lu, and J. Liu (2016), On the current density reduction ahead of dipolarization fronts, J. Geophys. Res. Space Physics, 121, 4269–4278, doi:10.1002/2016JA022754.

July 25, 2016:

THEMIS/ARTEMIS researcher awarded AGU Medal:

Toshi Nishimura (AOS/UCLA) is the recently announced recipient of the 2016 AGU Macelwane Medal! Toshi's work on substorms using THEMIS, ARTEMIS and ground based observatories has revolutionized our understanding of magnetosphere-ionosphere coupling, including topics such as flow burst coupling to north-south arcs, chorus wave coupling to pulsating aurorae and the role of polar cap transients in driving nightside reconnection (among other things). Congratulations Toshi!

James B. Macelwane Medal

The James B. Macelwane Medal is given annually to three or up to five honorees in recognition for "significant contributions to the geophysical sciences by an outstanding early career scientist." Established in 1961, the Macelwane Medal was renamed in 1986 in honor of former AGU president James B. Macelwane (1953–1956). Renowned for his contributions to geophysics, Macelwane was deeply interested in teaching and encouraging young scientists.

AGU Medal Recipients Press Release

About the James B. Macelwane Medal

June 20, 2016:

THEMIS study featured on cover of GRL, GEM Outstanding Student Poster Award:

UCLA PhD student Terry Z. Liu used THEMIS data from 2008 to profile the turbulent solar wind plasma upstream of the magnetosphere. Since the solar wind is moving at supersonic speeds, when it encounters the magnetopause, a collisionless shockwave forms. Some reflected ions can be energized to form a "foreshock bubble," which Terry found can in turn form its own foreshock. The two THEMIS probes happened to be in just the right place and time to witness the bubble and the reflected ions in close succession, helping to reveal the complex geometry of the plasma interactions. Way to go Terry!

A foreshock bubble's shock, GRL Cover image. Credit: Emmanuel Masongsong and Heli Hietala, UCLA; NASA EYES.

The image above is an artist's representation of a baby foreshock emerging from its parent foreshock. Incoming solar wind ion beams (blue arrows) get reflected (spiral purple arrows) at Earth's bow shock (red, far right). These reflected ions form Earth's parent foreshock (faint orange glow) and gradually become diffuse (blurred spiral purple arrows). In this study, a solar wind discontinuity was observed by the THEMIS-B spacecraft (far left), causing some of the reflected foreshock ions to become trapped and thermalized (center, purple arrows bending to become yellow arrows in random directions). These hot ions expand and form a foreshock bubble with a hot core (yellow) and its own shock (red) due to fast expansion. The THEMIS-C spacecraft (center) observed that this new shock can also reflect solar wind ion beams (blue arrows) and form a baby foreshock (spiral purple arrows with orange glow).

For more specific details, please refer to the THEMIS Science Nugget Summary here.

Liu, T. Z., H. Hietala, V. Angelopoulos, and D. L. Turner (2016), Observations of a new foreshock region upstream of a foreshock bubble's shock, Geophys. Res. Lett., 43, 4708–4715, doi:10.1002/2016GL068984.

February 25, 2016:

THEMIS featured in The Guardian, for new popular book on the aurora:

Featured in The Guardian: author and plasma physicist Dr. Melanie Windridge intertwines the cultural and scientific history of the aurora, and shares THEMIS mission breakthroughs in her new book, "Aurora: In Search of the Northern Lights​​​​​." Dr. Windridge reveals the rich history and enduring mysteries of the northern lights, from the ancient folklore of Arctic peoples to her own polar research adventures, elaborating on the latest findings about space weather and the complex mechanisms of the aurora. She also discusses the story behind the THEMIS mission, and the groundbreaking science fostered by its expansive array of All-Sky Imagers and magnetometers across the northern hemisphere, which continue to help researchers piece together critical elements of the auroral puzzle.

Credit: Harper Collins

"Canada has a vast amount of land underneath the auroral oval, so imaging the northern lights is an important research activity. This composite image from several cameras looking directly upwards shows how a twisted band of aurora can stretch all across the American continent. But it's not simply pretty. Our atmosphere is the screen where the drama of the magnetosphere plays out. By studying the aurora we can learn about the processes happening far out in space." -M. Windridge

Mosaic of the aurora from the THEMIS All-sky imagers. Credit: NASA GSFC/SVS

The Northern Lights Illuminated - in Pictures, featured on

The book was published by Harper Collins, more details can be found on the author's website.

June 15, 2015:

THEMIS observes first rising-tone magnetosonic waves:

Magnetosonic (MS) waves, also known as equatorial noise, are electromagnetic emissions occurring near the magnetic equator. They get their energy by interacting with protons trapped in Earth's magnetic field, spiraling around magnetic field lines. Historically, the frequencies of MS waves were believed to be "temporally continuous" - that is, varying smoothly, like a trombone player sliding from one note to the next. This indicated a simple linear interaction between MS waves and protons. Fu et al. report a possible complication to this picture: a sharp rising-tone in their spectrogram, like a flute player performing a series of runs and trills.

Top panel, actual MS rising tone data acquired by THEMIS. Bottom panel, artist rendition of THEMIS probes detecting MS waves within the ring current (magenta), near the boundary between the plasmasphere (green) and the outer Van Allen radiation belt (aqua).

A rising-tone suggests more complicated, nonlinear series of interactions between the MS waves and protons. Scientists have observed rising-tone features in other kinds of plasma waves, including chorus and electromagnetic ion cyclotron (EMIC) waves. In those waves, the web of forces between the particles create currents that boost the wave's frequency. But scientists had never before seen this behavior in MS waves. The team used data collected from two specific events recorded by NASA's THEMIS mission. The THEMIS spacecraft orbits in the magnetosphere near Earth's magnetic equator and collects data from magnetic storms, the boundary of the magnetosphere on the dayside, and Earth's radiation belts.

The first event, observed in June 2010, revealed electromagnetic emissions of rising-tone MS waves. Fu et al. studied a second rising-tone MS wave event, observed in August 2010, to eliminate the possibility that the previous rising-tone MS wave emissions were a one-time event. On the basis of the rising-tone feature of MS waves, the scientists concluded that MS waves were possibly generated from nonlinear interactions. The team found that the power of chorus and EMIC waves were less than those of the MS waves, indicating that protons interact less efficiently in those waves than with MS waves.

Zoomed in portion of a 3min span of rising tone MS waves captured by THEMIS-A on February 26, 2015.

In this video, you can listen to a sonification of the magnetosonic waves while following along on the above plot. Since the bass frequencies of these waves are at 80-120Hz near the lower limit of human hearing, the rising tone is subtle yet audible. Audio data produced by Huishan Fu with further processing by E. Masongsong.

For more specific details, please refer to the THEMIS Science Nugget Summary here.

Source: Research Highlights

Fu, H. S., J. B. Cao, Z. Zhima, Y. V. Khotyaintsev, V. Angelopoulos, O. Santolík, Y. Omura, U. Taubenschuss, L. Chen, and S. Y. Huang (2014), First observation of rising-tone magnetosonic waves, Geophys. Res. Lett., 41, 7419–7426, doi:10.1002/2014GL061867.

May 11, 2015:

THEMIS reveals surprising influence of Kelvin-Helmholtz waves on the magnetosphere:

Kelvin-Helmholtz waves are responsible for the "breaking wave" pattern made in clouds, the ocean's surface, and the swirling atmosphere of Jupiter. The periodic turbulence is caused by a velocity shear at the interface between two layers moving at different speeds, such as at the magnetopause, where the solar wind and magnetospheric plasma interact.

The figure is from an OpenGGCM magnetosphere simulation and shows, color coded, current density in the equatorial plane.

Using data from NASA's THEMIS mission, Joachim "Jimmy" Raeder and his Ph.D. student Shiva Kavosi of the University of New Hampshire found that K-H waves occur 20% of the time, can significantly alter the magnetopause and thus change the energy levels of our planet's radiation belts. The K-H waves can stimulate magnetospheric ultra-low frequency waves, which transfer energy from large-scale motions to alter the behavior of charged particles on tiny scales.

THEMIS data also show that K-H waves occur more often when the IMF is northward (~40%), though still significantly during southward IMF (~10%), which is much higher than previously detected. The waves are also found when least expected, during slow solar wind (~270km/s).

"Previous missions were either too short or the observations didn't occur in the right place," Raeder says. "THEMIS's elliptical orbits achieved over one thousand magnetopause crossings and provided unprecedented observations. We didn't have a database like this before and therefore couldn't do the analysis."

UNH Space Science Center Press Release

Kavosi, S., et al (2015), "Ubiquity of Kelvin-Helmholtz waves at Earth's magnetopause," Nature Comm., 6, 7019, doi:10.1038/ncomms8019.

February 17, 2015:

THEMIS results on plasmaspheric hiss featured in Journal of Geophysics Research:

Congratulations to Kyung-Chan Kim, Dae-Young Lee and Yuri Shprits for their featured JGR paper using THEMIS data, entitled "Dependence of plasmaspheric hiss on solar wind parameters and geomagnetic activity and modeling of its global distribution." The results demonstrate accurate modeling of plasmaspheric hiss waves in varying solar wind conditions.

Plasmaspheric hiss is a type of electromagnetic wave generally observed in the dense plasma region in the Earth's magnetosphere, and it affects the evolution of high energy electrons trapped around the Earth. Previous researchers have found the geomagnetic index, AE* (the maximum value of AE index during the preceding three hours) or Kp as the optimal input in hiss modeling. This work shows the direct correlation of the waves with the time-integrated, time-lagged solar wind parameters for the first time. The waves depend on past solar wind speed and southward interplanetary magnetic field. Hiss waves do not, in particular, depend on different types of storms (CME or CIR driven), based on their global distributions of occurrence rates.

Top panels: Variations of solar wind parameters and geomagnetic indices. Bottom panel: Model output of hiss amplitudes for CME-derived storm.

"To predict and understand plasma waves, we are using innovative data analysis tools that have become increasing popular in a number of areas of engineering and science," said co-author Yuri Shprits. "With the help of machine learning tools commonly referred to as 'neural networks' we can now rather accurately predict the properties of plasma waves, which helps us to predict the dynamics of relativistic electrons that are hazardous to satellites in space."

Citation: Kim, K.-C., D.-Y. Lee, and Y. Shprits (2015), Dependence of plasmaspheric hiss on solar wind parameters and geomagnetic activity and modeling of its global distribution, J. Geophys. Res. Space Physics, 120, doi:10.1002/2014JA020687.

January 19, 2015:

New book on magnetotail physics featuring THEMIS/ARTEMIS:

All magnetized planets in our solar system (Mercury, Earth, Jupiter, Saturn, Uranus, and Neptune) interact strongly with the solar wind and possess well developed magnetotails. It is not only the strongly magnetized planets that have magnetotails, however. Mars and Venus have no global intrinsic magnetic field, yet they possess induced magnetotails. Comets have magnetotails that are formed by the draping of the interplanetary magnetic field. In the case of planetary satellites (moons), the magnetotail refers to the wake region behind the satellite in the flow of either the solar wind or the magnetosphere of its parent planet.

The largest magnetotail of all in our solar system is the heliotail, the "magnetotail" of the heliosphere. The variety of solar wind conditions, planetary rotation rates, ionospheric conductivity, and physical dimensions provide an outstanding opportunity to extend our understanding of the influence of these factors on magnetotail processes and structures. In Magnetotails in the Solar System, all these magnetotails are described in tutorials and reviews.

Volume highlights include:

• Discussion on why a magnetotail is a fundamental problem of magnetospheric physics
• Unique collection of tutorials on a large range of magnetotails in our solar system
• In-depth reviews comparing magnetotail processes at Earth with other magnetotail structures found throughout the heliosphere
Citation: Keiling, A., C. Jackman, P. Delamere (Eds.) (2014), Magnetotails in the Solar System, Geophys. Monogr. Ser., vol. 207, 424 pp., AGU, Washington, D. C.

January 15, 2015:

THEMIS data shows "magnetic bubbles" may drive auroral substorms, AGU Research Spotlight:

The Earth's magnetic field extends out into space, influencing charged particles in a region known as the magnetosphere. The magnetosphere is short and squat on the side of earth that faces the sun – the dayside – but it has a long tail extending away from the star on the nightside. This magnetotail is shaped by the powerful force of the solar wind, and huge amounts of plasma flow within it. On Earth, we see the effects of this flow in the dazzling lights of the auroras.

Dramatic bursts of energy in the magnetotail, known as substorms, cause the aurora to flicker and dance when they send ions tumbling earthward, but their cause has long remained a mystery. Now Pritchett et al. propose that substorms may arise from the properties of Earth-sized "bubbles" of low–density plasma that ride magnetic field lines through the magnetotail toward Earth.

Left: Magnetic bubbles in the Earth's magnetotail, moving Earthward (down) to fuel substorms. Right: THEMIS all-sky imagers (ASI) record the evolution of a streamer in response to bubbles.

Using a computer model that simulates how charged particles behave in magnetic fields, the researchers show that these bubbles preferentially form in parts of the magnetotail where entropy decreases with distance from the Earth. The properties of these bubbles and the "auroral streamers" they send earthward change as they move through the magnetic field. Eventually, these changes trigger a full-blown substorm, disrupting the structure of the aurora.

The researchers' model helps explain the link between the magnetic perturbations that seem to accompany substorms and auroral streamers. Their predictions also match observations of the structure and behavior of auroral streamers made by NASA's Time History of Events and macroscale Interactions during Substorms (THEMIS) suite of satellites.

Source: Rosen, J. (2015), Bubbles as a possible mechanism behind magnetic substorms, Eos, 96(1):27.

Pritchett, P. L., F. V. Coroniti, and Y. Nishimura (2014), The kinetic ballooning/interchange instability as a source of dipolarization fronts and auroral streamers, J. Geophys. Res. Space Physics, 119, 4723–4739, doi:10.1002/2014JA019890.

December 19, 2015:

THEMIS results highlight wave-particle interactions in magnetized collisionless shocks:

In the 1960s, scientists discovered a new kind of shock wave that traveled through space plasmas that did not rely upon collisions. Thus, they are known as a collisionless shock waves. These shocks are of great interest in multiple fields of research: they can produce radiation that can negatively impact commercial and military spacecraft operation, as well as the safety of humans in space.

But the mechanisms allowing these shocks to form has been a topic of great debate. Our recent work helps resolve some of these issues by confirming theories that predict how small-scale phenomena can control large-scale dynamics. These small-scale processes, on the order of tens of meters, can regulate structures at scales more than 1 million meters across.

A shock wave produced by a jet approaching the sound barrier, outlined by condensed water droplets which result from the shockwave shedding from the aircraft (Wikipedia.)

Common shock waves – such as those at the front of a supersonic jet -- occur when an obstacle moves faster than the speed of sound, that is, the speed of a compression wave through a fluid. Such shocks transform the bulk flow from supersonic to subsonic in a thin transition region called the shock ramp, where the lost kinetic energy is converted into heat. With common shock waves, this conversion occurs mostly through binary particle collisions, much like billiard balls colliding and recoiling. In Earth's atmosphere, these collisions occur over a short distance, ~1μm, but in the solar wind and magnetized bow shock in front of Earth, the distance can be as large as that between the Earth and the sun (1AU, or around 150 billion meters). On the other hand, the magnetized shock ramps were found to be less than one-millionth that size. There was no way these shocks could rely upon particle collisions taking place over billions of meters -- thus the name collisionless shock wave. But how could such shocks transform the incident bulk flow into heat in such short distances without collisions?

Artist's depiction of the solar wind piling up in at the magnetosphere boundary, creating a collisionless shock wave.

The results were surprising. First, we discovered that not only are small-scale waves ubiquitous in collisionless shock waves -- but they can be huge. In some cases, the wave amplitudes were so large, they contained as much energy density as is necessary to produce an aurora. Second, we found that the energy dissipation rates due to wave-particle interactions were also very large. So large, in fact, that they could exceed the large-scale dissipation rates by over 10,000 times. In other words, the wave-particle interactions need only be ~0.01% efficient and they could still regulate the large-scale structure of the shock.

This information about waves near Earth can also be extrapolated to inaccessible regions of space. We found that similar processes could provide enough energy to explain the heating of the solar corona, magnetic reconnection rates, and have implications for particle heating and acceleration around stars elsewhere in the universe. These results quantitatively show, for the first time, that small-scale phenomena can control the large-scale dynamics in collisionless plasmas.

Citation: Wilson et al., "Quantified energy dissipation rates in the terrestrial bow shock: 1. Analysis techniques and methodology" and "Quantified energy dissipation rates in the terrestrial bow shock: 2. Waves and dissipation," Journal of Geophysics Research.

Source: Wilson, L.B., Helio Highlights Archive

August 7, 2014:

THEMIS researcher wins first prize in student poster competition:

The Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR) workshop was held June 22-26, 2014, at the University of Washington, Seattle. There were 129 CEDAR student presenters, including 21 undergraduate first authors, where 103 posters were in the student poster competition. Prizes were a certificate and a textbook for the first place winners.

The judges picked first place Ionosphere-Thermosphere winner Beatriz Gallardo-Lacourt of UCLA with "Ionospheric Flow Structures Associated with Auroral Beading at the Substorm Auroral Onset." She received the book "Ionospheres: Physics, Plasma Physics, and Chemistry" courtesy of co-author Bob Schunk (USU) who signed the book.

Bea's work showed that extremely large, small-scale flows develop in precise association with each auroral bead (strong intensification) that is seen along the brightening auroral arc at substorm onset. This demonstrates critical features of the physics of the substorm onset process.


June 1, 2014:

THEMIS researcher receives Young Scientist Award:

Japan's Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS) held a committee meeting on April 29, 2014 and made a decision to give the Obayashi Young Scientist Award to Yukitoshi Nishimura, for his research of magnetospheric and ionospheric phenomena using ground- and space-based measurements.

Toshi received this award as a result of his ground-breaking research on a variety of topics including energy flow to and from the ionosphere within the inner magnetosphere; fundamental, long-standing questions on the processes leading to an causing substorms; and the causes and magnetospheric source regions of pulsating and diffuse aurora.


May 1, 2014:

THEMIS research featured in Journal of Geophysics Research:

The recent paper by Gabrielse et al., "Statistical characteristics of particle injections throughout the equatorial magnetotail" was selected as an Editor's Highlight by JGR, Space Physics.

(a) AL index. (b) Energy flux. (c) Energy flux (line spectra). Note that the ESA instrument goes near background levels around 02:00, 03:00, and 06:30 UT, explaining the behavior of the fitted channel between the ESA and SST instruments (26 keV). To avoid incorrectly selecting an injection from the fitted channel, we required that the energy flux at 26 keV be higher than that at 31 keV for selection. (d) Percent change in energy flux per minute [((Δj/j)/Δt)˙100] for each individual energy channel. Colors represent energy channels and correlate with the colors in the line spectra. Three consecutive energy channels must have a (Δj/j)/Δt that rises above the horizontal line at 25% for an injection to be selected. (e) Magnetic field in GSM coordinates. Increasing dipolarization is observed as each dipolarized flux bundle comes in, causing flux pileup around 04:00 UT. (f) Velocity in GSM coordinates. Flow reversals may represent vortices in the incoming flow and/or rebound in the flux pileup region. (g) Electric field in GSM coordinates calculated from −V × B.
Gabrielse et al., Figure 1: Seven electron injection events selected using specific criteria. Events 1 and 2: Dispersionless injections. Events 3–7: Dispersed injections.

Understanding the behavior of charged particles in the magnetotail

When the Sun spews charged particles toward the Earth, they can enter the magnetosphere and become energized as they move closer to the Earth's surface. These energetic particles can induce the bright colors of auroras, disrupt navigational satellites, and even distort terrestrial telecommunications.

Previous research has found that the energization and transport of these particles—a process known as "particle injection"—may be correlated with the emergence of narrow, fast-flowing channels of plasma within the magnetosphere that travel earthward after energy is released in the Earth's magnetotail. Curious about how far out these particle injections can be detected in the magnetotail, and whether or not they are actually caused by these narrow, fast-flowing bursts of plasma, Gabrielse et al. studied data from NASA's THEMIS mission, which observes large-scale space weather events beyond the orbits of geosynchronous satellites.

The authors found that energetic particle injections could, in fact, be seen approaching Earth well beyond the previously recorded distance of 6.6-12 Earth radii, even up to 30 Earth radii away and possible further. They also showed statistically that these particle injections are indeed related to the narrow channels of fast-flowing plasma, where particles are energized by the flow channels' electric fields. Understanding how these particle injections behave at points within the radiation belts to distances greater than 30 Earth radii away will help scientists develop better forecasts of potentially damaging space weather events.

Also featured in JGR is a paper by Gallardo-Lacourt et al., "Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers."

Gallardo et al., Figure 1: Equatorward motion of the auroral streamer and the ionospheric flow channel obtained using the THEMIS ASI and Rankin Inlet SuperDARN radar on 14 January 2008. (a) The background flows before the auroral streamer propagated into the radar FOV. (b–g) The sequence of flow and auroral streamers. The solid blue line indicates magnetic midnight. The white lines correspond to 75 and 70 MLAT contours, respectively.

In their JGR featured article, Gallardo-Lacourt et al. [2014] investigated the structure of ionospheric "flow channels" and their relationship to the aurora, using THEMIS all-sky imagers and SuperDARN radar network. Auroral streamers observed by the all-sky images were invariably linked to equatorward ionospheric flow enhancements located to the east and poleward flow enhancements to the west of the streamer, consistent with the spatial relationship between flow shear and upward field-aligned current in the plasma sheet "flow bursts."

We are very proud of Christine and Bea's accomplishments and look forward to their continued successes!

JGR Editor's Highlight: Understanding the behavior of charged particles in the magnetotail

Gabrielse, C., V. Angelopoulos, A. Runov, and D. L. Turner (2014), Statistical characteristics of particle injections throughout the equatorial magnetotail, J. Geophys. Res. Space Physics, 119, 2512–2535, doi:10.1002/2013JA019638.

Gallardo-Lacourt, B., Y. Nishimura, L. R. Lyons, S. Zou, V. Angelopoulos, E. Donovan, K. A. McWilliams, J. M. Ruohoniemi, and N. Nishitani (2014), Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers, J. Geophys. Res. Space Physics, 119, 142–150, doi:10.1002/2013JA019245.

March 7, 2014:

THEMIS observations of the plasmaspheric plume published in Science:

(Click for Animation) NASA's THEMIS mission observed how dense particles normally near Earth in a layer of the uppermost atmosphere called the plasmasphere can send a plume up through space to help protect against incoming solar particles during certain space weather events. Credit NASA/GSFC

Using THEMIS magnetopause observations and GPS-TEC measurements, Walsh et al. characterized the plasmaspheric plume and its modulating effect on dayside magnetic reconnection. The findings were published today in the journal Science. The Earth's magnetic field, or magnetosphere, stretches from the planets core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect the Earth from this high-energy solar activity. But when this field comes into contact with the sun's magnetic field — a process called "magnetic reconnection" — powerful electrical currents from the sun can stream into Earth's atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.

In the March 7, 2014, issue of Science, Walsh and collaborators at MIT and NASA identified a process in the Earth's magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay. By comparing observations from the ground and in space during a solar storm, they could characterize the solar wind energy as it crossed the boundary into the magnetosphere through reconnection.

Closer to Earth, there is a region of cold dense gas at the very top of our atmosphere, called the plasmasphere. GPS signals travel through the plasmasphere at different speeds depending on how thick or thin the plasmasphere is along the journey. Tracking the GPS radio signals, therefore, can help researchers map out the properties of the plasmasphere.

In combination with THEMIS data, the researchers showed that the tongue of this cold, dense plasmasphere material stretched all the way up to interfere with the magnetic reconnection point where the CME had made contact with the magnetopause. NASA's three THEMIS spacecraft were in the right place at the right time, flying through the magnetosphere's boundary approximately 45 minutes apart, and caught this interaction.The three sets of THEMIS observations demonstrated that the plume had a dramatic impact on the characteristics of the magnetic reconnection region, revealing a critical regulatory mechanism of magnetosphere interactions with the solar wind.

NASA's THEMIS Discovers New Process that Protects Earth from Space Weather (

A river of plasma, guarding against the sun (MIT News Office)

Walsh, B.M., J.C. Foster, P.J. Erickson, D.G. Sibeck (2014), Simultaneous Ground- and Space-Based Observations of the Plasmaspheric Plume and Reconnection, Science 343(6175): 1122-1125, DOI: 10.1126/science.1247212

Nov. 26, 2013:

THEMIS findings featured in AGU Journal Eos:

Electron heating in magnetic reconnection.

When magnetic field lines interact at the magnetopause—the boundary between the solar magnetic field and the Earth's magnetic field—a process known as magnetic reconnection causes magnetic energy to be converted into kinetic energy and heat. Magnetic reconnection is a collisionless process, and its dynamics are still not fully understood. Past studies of reconnection have produced conflicting findings as to whether, and, if so, how much, reconnection heats electrons. Although reconnection has been found to heat electrons to 10 million kelvins in the Earth's magnetotail, it does not appear to heat electrons in the solar wind.

Drawing on observations of 79 instances of magnetic reconnection as recorded by NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites, Phan et al. studied the extent to which various physical properties affect the magnitude and occurrence of electron bulk heating. The authors found that bulk electron heating depends primarily on the amount of available magnetic energy in the solar wind.

From their observations the authors empirically determined that around 2% of the magnetic energy in the solar wind is converted to bulk electron heating. This finding, they suggest, may be uinversal for plasmas in space as well as in the laboratory. It could help explain why there is strong electron heating in the Earth's magnetotail but essentially no heating in the solar wind during reconnection. They suggest that it could also be used to investigate the role of magnetic reconnection in heating the solar corona.

Sources: Eos Research Spotlight

Phan, T. D., M. A. Shay, J. T. Gosling, M. Fujimoto, J. F. Drake, G. Paschmann, M. Oieroset, J. P. Eastwood, and V. Angelopoulos (2013), Electron bulk heating in magnetic reconnection at Earth's magnetopause: Dependence on the inflow Alfvén speed and magnetic shear, Geophys. Res. Lett., 40, 4475–4480, doi:10.1002/grl.50917.

Nov. 8, 2013:

THEMIS-MMS Conjunctions: A Step Closer to Reality:

The recent maneuver campaign for the three THEMIS probes has been completed, and recent orbit determination has confirmed the maneuvers have been 100% successful. Between Sep. 25, 2013 and Oct. 22, 2013 we have executed a total of 19 maneuvers: There were 4 orbit change maneuvers, one attitude, and one spin rate adjustment per probe, and on September 24, we had our first ever collision avoidance maneuver for P3PD with a zero net change of the orbital period.

By lowering perigee and apogee altitudes we further increased our orbital drift. This final step in our preparation for the upcoming conjunctions with MMS in 2016 and 2017, originally planned for July, was delayed multiple times until early MMS thermal vacuum test results confirmed there are no major hurtles towards an MMS launch in late 2014. By doing so we traded as much as possible of our valuable drift time against the ability to account for a possible major launch delay of MMS into spring 2015 (which would have required imparting a drift in the reverse direction). Despite the recent MMS launch delay by one month there is still room for adjustments to preserve good quality lineups. We are therefore optimistic that we can still take full advantage of this very unique opportunity of THM-MMS conjunctions.

For the near term cooperation with the Van Allen Probes we increased the probe separation to about 7.5h. This nearly equal spread along the orbit was achieved through specific relative timing of the MMS-lineup maneuvers. And as you may have noticed, FS intervals have increased in duration to more typical 18-20hrs recently, thanks to the use of the White Sands antenna (thank you NASA).

All probes are in a clean spin rate window (low interference with FGM) and the attitudes have been optimized for the tail season in 2014 (sunward spin axis tilt) when we plan to return to smaller separations to obtain a second batch of 1-2Re inter-probe separation data. For the long term, THEMIS is on its way to be in the magnetotail during winter of 2016 and 2017 while again in conjunction with the GBOs! This will be an amazing opportunity to conduct Heliophysics System Observatory magnetotail studies.

Soon, there will be an update at SPDF, projecting the near and long term plans of THEMIS based on the post maneuver states. The current data at SPDF reflect the older long term plans based on only earlier maneuvers (from July), but will be updated soon. By having MMS orbits at SPDF as well, we plan to seek community feedback on how to best optimize the tetrahedral configuration of THEMIS around MMS.

We would like to use this opportunity to thank all of you who supported these maneuvers and in particular the flight dynamics, scheduling, and operation teams. We are confident that science will be well served with the outcome of all their hard work and that NASA will get the confirmation that their further support for THEMIS was worth their funding.

Sept. 22, 2013:

Third radiation belt formation:

(Click here for animation of third belt)

Congratulations to Yuri Shprits and colleagues for explaining the mechanism of creation of the remnant belt, a 3rd radiation belt in Earth's magnetosphere using a combination of THEMIS, Van Allen probes data and modeling. The results, which appear on the Sep. 22 (2013) issue of Nature Phys. go a long way towards revealing the separate physical processes that affect different electron belts, including wave scattering, and the effects of cold plasmaspheric plasma.

Since the discovery of the Van Allen radiation belts in 1958, space scientists have believed these belts encircling the Earth consist of two doughnut-shaped rings of highly charged particles — an inner ring of high-energy electrons and energetic positive ions and an outer ring of high-energy electrons.

In February of this year, a team of Van Allen Probes scientists reported the surprising discovery of a previously unknown third radiation ring — a narrow one that briefly appeared between the inner and outer rings in September 2012 and persisted for a month (Baker et al., Science, Feb. 2013).

The above Van Allen Probe 2013 results confirmed earlier observations by THEMIS researchers (Turner et al., Nature Physics, Jan. 2012), showing the rapid loss of outer belt electrons through the magnetopause, creating a distinct "remnant" belt. The remnant belt has a lifetime of hours to days for low energy (<2MeV) particles, that is dictated by the particle losses due to various plasma waves (hiss or electromagnetic ion cyclotron – EMIC - waves). However, an equatorial >2MeV population, was present in the Van Allen Probe 2013 study event for many weeks. The new modeling results by Shprits et al., show what causes the stability of the equatorial >2MeV electrons: it is the presence of the plasmasphere that protects these particles from EMIC waves, and the lack of resonance of these particles with hiss waves inside the plasmasphere.

"In the past, scientists thought that all the electrons in the radiation belts around the Earth obeyed the same physics," said Yuri Shprits, a research geophysicist with the UCLA Department of Earth and Space Sciences. "We are finding now that radiation belts consist of different populations that are driven by very different physical processes."


Nature Physics:

March 28, 2013:

THEMIS/ARTEMIS International Team Sees Auroras:

The Spring THEMIS-ARTEMIS Science Working Group meeting brought researchers together from all over the world to share the latest findings on the magnetosphere, solar wind, and the moon. Even better, attendees were rewarded with a substorm and brilliant auroras on the closing night! The truly diverse group of 50+ space and atmospheric physics scientists represented 7 countries and 24 different institutions, all coming together to share the latest findings in the near-Earth plasma environment. The meeting discussions were inspiring and productive, though the greatest thrill was during a visit to the Poker Flat Research Range just north of Fairbanks. Even after decades of studying space physics, this was the first opportunity for many to witness the auroras' dazzling beauty in person.

At this state of the art facility, researchers stayed warm indoors (outside temp was -20F!) while patiently monitoring real-time solar wind measurements and ultra-sensitive CCD cameras displays. Periodically they would jump with excitement and a whir of outer garments as the early signs of a substorm appeared. Many were awestruck at their first sighting, and remarked on the surprising speed with which the green arcs consumed the sky. Many thanks to meeting organizer Dr. Hui Zhang and Dr. Don Hampton of University of Alaska for the Poker Flat tour, and to all attendees for their continuing contributions to THEMIS/ARTEMIS!!

(click thumbnails to enlarge)

February 19, 2013:

THEMIS 6th Year Anniversary:

Six Years in Space for THEMIS: Understanding the Magnetosphere Better Than Ever

On Earth, scientists can observe weather patterns, and more importantly can predict them, through the use of tens of thousands of weather observatories scattered around the globe. Up in the space surrounding Earth -- a space that seethes with its own space weather made of speeding charged particles and constantly changing magnetic fields that can impact satellites - there are only a handful of spacecraft to watch for solar and magnetic storms. The number of observatories has been growing over the last six years, however. Today these spacecraft have begun to provide the first multipoint measurements to better understand space weather events as they move through space, something impossible to track with a single spacecraft.

Helping to anchor that team of spacecraft is a NASA mission called THEMIS (Time History of Events and Macroscale Interactions during Substorms). THEMIS launched on Feb. 17, 2007, with five nearly identical spacecraft nestled inside a Delta II rocket. Simply orchestrating how to expel each of the five satellites without unbalancing the rocket was an engineering tour de force - but it was only the preamble. Over time, each spacecraft moved into formation to fly around Earth in a highly-elliptical orbit that would have them travelling through all parts of Earth's space weather environment, a giant magnetic bubble called the magnetosphere. With five different observatories, scientists could watch space weather unfold in a way never before possible.

In its sixth year in space, scientific papers using THEMIS data helped highlight a number of crucial details about what causes space weather events in this complex system.

"Scientists have been trying to understand what drives changes in the magnetosphere since the 1958 discovery by James Van Allen that Earth was surrounded by rings of radiation," says David Sibeck, project scientist for THEMIS at NASA's Goddard Space Flight Center in Greenbelt, Md. "Over the last six years, in conjunction with other key missions such as Cluster and the recently launched Van Allen Probes to study the radiation belts, THEMIS has dramatically improved our understanding of the magnetosphere."

Since that 1958 discovery, observations of the radiation belts and near Earth space have shown that in response to different kinds of activity on the sun, energetic particles can appear almost instantaneously around Earth, while in other cases they can be wiped out completely. Electromagnetic waves course through the area too, kicking particles along, pushing them ever faster, or dumping them into the Earth's atmosphere. The bare bones of how particles and waves interact have been described, but with only one spacecraft traveling through a given area at a time, it's impossible to discern what causes the observed changes during any given event.

"Trying to understand this very complex system over the last 40 years has been quite difficult," says Vassilis Angelopoulos, the principal investigator for THEMIS at the University of California in Los Angeles (UCLA). "But very recently we have learned how even small variations in the solar wind - which buffets Earth's space environment at a million miles an hour -- can sometimes cause extreme responses, causing more particles to arrive or to be lost."

Near Earth, THEMIS has now traveled through more than 50 solar storms that caused particles in the outer radiation belts to either increase or decrease in number. Historically, it has been difficult for scientists to find commonalities between such occurrences and discover what, if anything consistently caused an enhancement or a depletion. With so many events to study, however, and a more global view of the system from several spacecraft working together - including, in this case, ground based observations and NOAA's GOES (Geostationary Operational Environment Satellites) and POES (Polar Operational Environmental Satellites) data in addition to THEMIS data - a team of scientists led by Drew Turner at UCLA could better characterize what processes caused which results.

Turner's group recently presented evidence linking specific kinds of electromagnetic waves in space - waves that are differentiated based on such things as their frequencies, whether they interact with ions or electrons, and whether they move along or across the background magnetic fields - to different effects. Chorus waves, so called because when played through an amplifier they sound like a chorus of singing birds, consistently sped up particles, leading to an increase in particle density. On the other hand, two types of waves known as hiss and EMIC (Electromagnetic Ion Cyclotron) waves occurred in those storms that showed particle depletion. Turner also observed that when incoming activity from the sun severely pushed in the boundaries of the magnetosphere this, too, led to particle drop outs, or sudden losses throughout the system. Such information is helpful to those attempting to forecast changes in the radiation belts, which if they swell too much can encompass many of our spacecraft.

Another group has a paper in print in 2013 based on 2008 data from the five THEMIS spacecraft in conjunction with three of NOAA's GOES (Geostationary Operational Environmental Satellites) spacecraft, and the ESA/NASA Cluster mission. Led by Michael Hartinger at the University of Michigan in Ann Arbor, this group compared observations at the bow shock where the supersonic solar wind brakes to flow around the magnetosphere to what happens inside the magnetosphere. They found that instabilities drive perturbations in the solar wind particles streaming towards the bow shock and that these perturbations can be correlated with another type of magnetized wave - ULF (ultra low frequency) waves -- inside the magnetosphere. ULF waves, in turn, are thought to be important for changes in the radiation belts.

"The interesting thing about this paper is that it shows how the magnetosphere actually gets quite a bit of energy from the solar wind, even by seemingly innocuous rotations in the magnetic field," says Angelopoulos. "People hadn't realized that you could get waves from these types of events, but there was a one-to-one correspondence. One THEMIS spacecraft saw an instability at the bow shock and another THEMIS spacecraft then saw the waves closer to Earth."

Since all the various waves in the magnetosphere are what can impart energy to the particles surrounding Earth, knowing just what causes each kind of wave is yet another important part of the space weather puzzle.

A third interesting science paper from THEMIS's sixth year focused on features originating even further upstream in the solar wind. Led by Galina Korotova at IZMIRAN in Troitsk, Russia, this work made use of THEMIS and GOES data to observe the magnetosphere boundary, the magnetopause. The researchers addressed how seemingly small perturbations in the solar wind can have large effects near Earth. Wave-particle interactions in the solar wind in the turbulent region upstream from the bow shock act as a gate valve, dramatically changing the bow shock orientation and strength directly in front of Earth, an area that depends critically on the magnetic field orientation. The extreme bow shock variations cause undulations throughout the magnetopause, which, launch pressure perturbations that may in turn energize particles in the Van Allen radiation belts.

All of this recent work helps illuminate the nitty gritty details of how seemingly small changes in a system can lead to large variations in the near-Earth space environment where so many important technologies - including science, weather, GPS and communications satellites all reside.

Much of this work was based on data from when all five spacecraft were orbiting Earth. Beginning in the fall of 2010, however, two of the THEMIS spacecraft were moved over the course of nine months to observe the environment around the moon. These two satellites were renamed ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun). In their new position, the two ARTEMIS spacecraft spend 80% of their time directly observing the solar wind, offering a vantage point on this area outside our magnetosphere that is quite close to home.

The THEMIS spacecraft continue to work at their original levels of operation and all the instruments function highly effectively. With their current positioning and the ability to work in conjunction with other nearby spacecraft, scientists look forward to the stream of data yet to come.

"What we have with THEMIS and ARTEMIS and the Van Allen Probes, is a whole constellation we are developing in near-Earth space," says Turner. "It's crucial for developing our forecasting ability and getting a better sense of the system as a whole."

THEMIS is the fifth medium-class mission under NASA's Explorer Program, which was conceived to provide frequent flight opportunities for world-class scientific investigations from space within the Heliophysics and Astrophysics science areas. The Explorers Program Office at Goddard manages this NASA-funded mission. The University of California, Berkeley's Space Sciences Laboratory and Swales Aerospace in Beltsville, Md., built the THEMIS probes.

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, MD.

Source: NASA News:

February 14, 2013:

THEMIS featured in AGU Geophysical Monograph:

A new AGU Monograph on auroral physics was recently published, prominently featuring THEMIS data. While in the past terrestrial and planetary auroras have been largely treated in separate books, Auroral Phenomenology and Magnetospheric Processes: Earth and Other Planets takes a holistic approach, treating the aurora as a fundamental process and discussing the phenomenology, physics, and relationship with the respective planetary magnetospheres in one volume. While there are some behaviors common in auroras of the different planets, there are also striking differences that test our basic understanding of auroral processes. The objective, upon which this monograph is focused, is to connect our knowledge of auroral morphology to the physical processes in the magnetosphere that power and structure discrete and diffuse auroras. The volume synthesizes five major areas: auroral phenomenology, aurora and ionospheric electrodynamics, discrete auroral acceleration, aurora and magnetospheric dynamics, and comparative planetary aurora. Covering the recent advances in observations, simulation, and theory, this book will serve a broad community of scientists, including graduate students, studying auroras at Mars, Earth, Saturn, and Jupiter.

Many spacecraft missions have probed the outer magnetosphere of Earth in conjunction with ground-based and space-borne imagers, and these have contributed enormously to our understanding of the coupled magnetotail-ionosphere system. It must also be said that the THEMIS project has given a new boost to the ongoing auroral investigations, and thus it is features prominently in this volume.

Citation: Keiling, A., E. Donovan, F. Bagenal, and T. Karlsson (Eds.) (2012), Auroral Phenomenology and Magnetospheric Processes: Earth and Other Planets, Geophys. Monogr. Ser., vol. 197, 443 pp., AGU, Washington, D. C., doi:10.1029/GM197.

October 6, 2012:

THEMIS Research Highlight:

Congratulations to our colleague Victor Sergeev of St. Petersburg University! The editors of the Journal of Geophysical Research - Space Physics have selected his recent paper based on THEMIS data, entitled "Energetic particle injections to geostationary orbit: Relationship to flow bursts and magnetospheric state," as a JGR Editor's Highlight. It will also be featured as a "Research Spotlight" in Eos, AGU's weekly newspaper, to be published soon.

Most high-energy particle injections do not reach geostationary orbit

The injection of high-energy particles into the inner magnetotail is often considered a reliable sign of a magnetic substorm. These injections are often thought to be caused by flow bursts, short-lived periods of narrow fast flow streams in the magnetotail. Analyzing records of flow bursts at the entry to the night-side inner magnetosphere, from 8 to 13 Earth radii, as seen by Geotail from 1995 to 2005, and by the Time History of Events and Macroscale Interactions During Substorms (THEMIS) satellite from 2008 to 2009, Sergeev et al. (2012) found that most flow bursts do not cause the injection of high-energy particles to geostationary altitudes, and thus such injections are a poor measure of substorm activity. The authors identified 61 flow bursts using the Geotail records, and 44 using THEMIS observations. To determine whether an injection occurred with each of the flow bursts, they compared the Geotail records with publicly accessible pre-2008 particle injection data from Los Alamos National Laboratory (LANL) satellites, and turned to LANL scientists who had access to classified LANL satellite observations to confirm whether or not an injection occurred with each of the flow bursts in the THEMIS observations. The authors found that only 23 of the 61 Geotail bursts and 16 of the 44 THEMIS bursts were associated with the injection of high-energy particles into geostationary Earth orbit. The authors found that for a particle injection to make it to geostationary altitudes, the entropy parameter in the flow burst plasma needed to be comparable to the entropy at geostationary Earth orbit. The authors found that a strong solar wind driving, and high plasma pressure, at geostationary orbit could help drive up geostationary entropy and allow the injection of accelerated flow burst plasma.

X-Y locations of the spacecraft observing the flow bursts for two data sets. Thick curve shows the GEO distance (6.6 Re). (a) Geotail locations in the events accompanied by GEO injections (red points) and in those without GEO injections (blue points). (b) Same as Figure 2a but for THEMIS spacecraft; events with simultaneous observations at two or three spacecraft are connected by line segments.

Citation: Sergeev, V. A., I. A. Chernyaev, S. V. Dubyagin, Y. Miyashita, V. Angelopoulos, P. D. Boakes, R. Nakamura, and M. G. Henderson (2012), Energetic particle injections to geostationary orbit: Relationship to flow bursts and magnetospheric state, J. Geophys. Res., 117, A10207, doi:10.1029/2012JA017773.

September 19, 2012:

UCLA THEMIS Research Highlight:

The editors of the journal Geophysical Research Letters have selected Lunjin Chen's recent paper, entitled "Modulation of plasmaspheric hiss intensity by thermal plasma density structure," as both a GRL Editor's Highlight and a feature in the "Research Spotlight" section on the back page of Eos, AGU's weekly newspaper.

Plasmaspheric hiss amplification mechanisms identified (by Colin Schultz, from Eos)

Over the past 3 decades the hypothesis that chorus waves- a form of highintensity plasma wave often found in the outer magnetosphere- evolve into plasmaspheric hiss in the plasmasphere has grown in prominence. Plasmaspheric hiss is a form of low-frequency radio wave that is often observed in the regions within the plasmasphere that have high plasma densities. Plasmaspheric hiss is important in that the hiss waves interact with highenergy electrons in Earth's geomagnetic field, carving out a swath between the inner and outer Van Allen radiation belts to form the "slot region," a relative safe zone with minimized radiation hazard. Though modeled simulations of plasmaspheric hiss formation from chorus waves have been able to reproduce the major properties of observed hiss, they often underestimate hiss intensity by 10-20 decibels. Drawing on observations from the planet's dayside made using NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite, Chen et al. examine two mechanisms that could make up for this shortfall.

A representative chorus ray that is guided by a density crest. The magenta line represents the ray path, along which wave normal directions are denoted by the short segments color-coded by the propagation time (up to 17 seconds). The model plasma density is shown in the background in gray scale.

Citation: Chen, L., R. M. Thorne, W. Li, J. Bortnik, D. Turner, and V. Angelopoulos (2012), Modulation of plasmaspheric hiss intensity by thermal plasma density structure, Geophys. Res. Lett., 39, L14103, doi:10.1029/2012GL052308.

June 26, 2012:

Jenni Kissinger's paper highlighted by JGR and Eos:

The editors of the Journal of Geophysical Research - Space Physics have selected Jenni Kissinger's recent paper, entitled "Diversion of plasma due to high pressure in the inner magnetosphere during steady magnetospheric convection," as both a JGR Editor's Highlight and a feature in the "Research Spotlight" section on the back page of Eos, AGU's weekly newspaper.

Steady convection keeps Earth's magnetic field in balance (by Colin Schultz, from Eos)

The onslaught of the solar wind on the Sun-facing side of Earth's magnetic field causes terrestrial magnetic field lines to break through magnetic reconnection. The persistent pressure of the solar wind pulls the field lines and the associated plasma around to the magnetotail on Earth's nightside, where magnetic reconnection occurs once again to form the plasma sheet region. This uneven distribution creates a pressure gradient that drives nightside plasma back toward the planet. The Earthward transport of this nightside magnetospheric plasma is known to occur in one of two ways: as a magnetic substorm or as steady magnetospheric convection (SMC). Substorms include acute inflows that cause plasma to pile up in the inner magnetosphere and have been tied to the onset of aurorae. SMC, on the other hand, has been proposed as a mechanism for rebalancing the plasma gradient established between the day and night sides of Earth's magnetic field. Kissinger et al. compiled 14 years of magnetic field and plasma observations to study how plasma flows and magnetospheric conditions differ between SMC events and substorms.

Contour maps of average Earthward magnetic flux transport in the X-Y GSM plane by type of activity: (top) quiet, pre-SMC, and SMC and (bottom) substorm growth, expansion, and recovery. All plots are to the same color scale.

Citation: Kissinger, J., R. L. McPherron, T.-S. Hsu, and V. Angelopoulos (2012), Diversion of plasma due to high pressure in the inner magnetosphere during steady magnetospheric convection, J. Geophys. Res., 117, A05206, doi:10.1029/2012JA017579.

June 7, 2012:

Lunjin Chen receives AGU Fred L. Scarf award for THEMIS work:

Congratulations to Lunjin Chen for winning the Fred L. Scarf award for the best 2011 PhD thesis in AGU's Space Physics and Aeronomy section, recognizing outstanding dissertation research that contributes directly to solar-planetary science. His thesis, entitled "Propagation and Excitation of Electromagnetic Waves in the Earth's Inner Magnetosphere," benefited significantly from the availability of THEMIS data. He will be receiving his award at the Fall AGU meeting.

Citation: Chen, Lunjin, Propagation and Excitation of Electromagnetic Waves in the Earth's Inner Magnetosphere, University of California, Los Angeles, 2011 , 247 pages; AAT 3483236.

May 1, 2012:

THEMIS/ARTEMIS featured on cover of Geophysical Research Letters:

A THEMIS/ARTEMIS mission spacecraft (P1) and Jimmy Raeder's simulation rendition of a THEMIS major conjunction are prominently featured on the cover of today's (March 16, 2012, Vol. 39, No. 5) issue of Geophysical Research Letters. This happened thanks to the review paper on substorm research by Victor Sergeev and colleagues which is published in this same issue.

Congratulations to Victor on his paper and to the THEMIS/ARTEMIS communities for continuing the great pace of discoveries on substorms and so many other topics spanning the entire magnetosphere (and which are increasingly including the storms of the current solar cycle!).

Link to journal:
Cover image: JPG - PDF

Citation: Sergeev, V. A., V. Angelopoulos, and R. Nakamura (2012), Recent advances in understanding substorm dynamics, Geophys. Res. Lett., 39, L05101, doi:10.1029/2012GL050859.

Magnetosphere simulation with THEMIS spacecraft conjuction in the equatorial plane.
Credit: J. Raeder (UNH), NASA/Goddard Scientific Visualization Studio.

January 29, 2012:

THEMIS research published in Nature Physics Journal:

Congratulations to Drew Turner for his Nature Physics publication on: "Explaining sudden losses of outer radiation belt electrons during geomagnetic storms" published on-line on January 29 and making the news around the world!

Using combined data from THEMIS, GOES, and NOAA-POES satellites, Dr. Turner's research explains how electron losses through the magnetopause resolve a long standing mystery of electron drop-outs during storm main phase.

Read the article here:
NASA press release:

Source: Turner, D. L., Y. Shprits, M. Hartinger, V. Angelopoulos (2012), Explaining sudden losses of outer radiation belt electrons during geomagnetic storms, Nature Phys., doi:10.1038/nphys2185.

From October to December 2003, the radiation belts swelled and shrank in response to geomagnetic storms as particles entered and escaped the belts. Credit: NASA/Goddard Scientific Visualization Studio

January 17, 2012:

THEMIS analyses highlighted in AGU's Eos magazine:

The editors of the Journal of Geophysical Research - Space Physics have selected Dr. Larry Lyons' recent paper, entitled "Possible connection of polar cap flows to pre- and post-substorm onset PBIs and streamers" as an AGU "Research Spotlight."

The general summary (below) of the paper will be published in JGR online and in the "Research Spotlight" section on the back page of Eos, AGU's weekly newspaper. These summaries are designed to highlight new, noteworthy, and interesting results published in AGU's journals. Congratulations to Dr. Lyons and his team on their accomplishment!

Flows in polar cap ionosphere could trigger auroral substorms

Auroral substorms, in which aurora brighten and increase in speed, occur often and seem to be triggered by electric currents in the ionosphere at high latitude. However, scientists don't know the details of how auroral substorms begin and what drives their expansion and controls their duration.

Plasma flows within the ionosphere's polar cap region hadn't generally been considered to be a driver of auroral substorms, but some recent studies have suggested that mesoscale plasma flows from the polar cap could cross the polar cap boundary and contribute to triggering of flows that may bring new plasma earthward and lead to onset of substorms.

Lyons et al. used the Resolute Bay incoherent scatter radar and the Rankin Inlet PolarDARN radar, combined with all sky images from the THEMIS satellites, to study plasma flows in the polar cap. They observed flows moving from within the polar cap toward the polar cap boundary. The authors believe that their observations provide evidence that such flow structures could be important for triggering other flows that lead to onset of substorms. In addition, they suggest that flows in the polar cap after substorm onset could be important in controlling poleward expansion and continuation of auroral activity after a substorm has begun. The study could lead to better understanding of how auroral substorms begin.

Source: Lyons, L. R., Y. Nishimura, H.-J. Kim, E. Donovan, V. Angelopoulos, G. Sofko, M. Nicolls, C. Heinselman, J. M. Ruohoniemi, and N. Nishitani (2011), Possible connection of polar cap flows to pre- and post-substorm onset PBIs and streamers, J. Geophys. Res., 116, A12225, doi:10.1029/2011JA016850.

Figure 1. Schematic illustration of motion of pre-onset auroral forms and their relation to nightside ionospheric convection and flow channels based on Nishimura et al. [2010b]. The pink star, NS oriented pink line, and azimuthally extended wavy lines indicate a poleward boundary intensification (PBI), an auroral steamer, and an onset arc, respectively. Blue arrows illustrate the plasma flow pattern inferred by Nishimura et al. and from the polar cap flow observations considered here. Numbers 1-4 show the time sequence of pre-onset phenomena discussed in this paper. Yellow and mottled shading, respectively, correspond to the regions of proton and electron precipitation, SAPS refers to the region of sub-auroral polarization streams that lies equatorward of the inner edge of plasma sheet electron precipitation, and black curves represent the large-scale background convection flow pattern.

September 23, 2011:

Substorm Perspectives with Modern Magnetospheric and Ground Observatories:

The much anticipated proceedings book/CD from the 10th International Conference on Substorms (ICS10) where THEMIS was prominently featured, is now available. Copies will be mailed out to attendees shortly. A few extra copies for non-attendees are also available on a first come first serve basis by request to

Click here to view articles.

July 18, 2011:

ARTEMIS P2 finally arrives at its new home:

On July 17th, 2011 the second probe P2 of the ARTEMIS mission successfully entered orbit around the moon after a circuitous 2-year journey from Earth orbit. Shortly after the two probes completed their original mission studying Earth's magnetic field in 2009 (THEMIS), they were propelled using carefully designed gravity-assist maneuvers to farther and farther orbits. Due to Earth's impending unacceptably long shadows, the spacecraft took refuge in the Lagrangian points on either side of the moon. ARTEMIS P1 and P2 were the first spacecraft ever to use those complex orbits operationally.

After using the Lagrange orbits as observational outposts for 9 months, the two spacecraft were subsequently staged to enter into stable lunar orbits. The P1 probe entered lunar orbit on June 27th, 2011, and now with its twin P2 orbiting in the opposite direction around the moon, the pair's sensitive instruments will yield the first 3D measurements of the moon's magnetic field to determine its regional influence on solar wind particles.

Read more about the ARTEMIS mission here:

ARTEMIS-P2 insertion into lunar orbit on Sunday July 17, 2011. The orbit is shown in a fixed Earth-Moon frame (horizontal axis, Earth to the left), viewed from above the ecliptic. Tickmarks are one-day intervals. P2 is leaving its prior trajectory, hovering in the Lagrange point between Earth and Moon (centered at L1 in the figure) to now enter a stable lunar orbit, its final destination. The P2 thrusters will be fired during three concecutive intervals lasting about 3 hrs at the time of the lunar orbit insertion (LOI), indicated by the red trace.

Credit: NASA/Goddard Space Flight Center.

June 27, 2011:

ARTEMIS/P1 now successfully inserted into Lunar Orbit.:

This morning ARTEMIS P1 (a.k.a. THEMIS B) was successfully inserted into a lunar orbit. The maneuver sequence stored onboard the spacecraft executed nominally near periselene on 2011/178 from 14:04 to 16:31 UTC, slowing the spacecraft by 50.3 m/s and allowing gravity capture into an initial orbit with estimated periselene and aposelene radii of approximately 3,543 and 27,000 km, respectively.

This was a great team effort so far, and our special thanks go out to the JPL and GSFC navigation and flight dynamics teams, as well as to all who helped us with networks support, in particular the DSN team. We could not have accomplished this without you!

Manfred Bester
Mission Operations Manager
Space Sciences Laboratory, UC Berkeley

See NASA Press release here:

View from above the ARTEMIS P1 orbit as it transitions from the kidney-shaped Lissajous orbit to orbiting around the moon.
Credit: NASA/Goddard Space Flight Center.

March 11, 2011:

THEMIS at AGU Chapman Conference:

THEMIS data were prominently presented during the recent AGU Chapman conference on the Relationship between Auroral Phenomenology and Magnetospheric Processes, held in Fairbanks, Alaska, from February 27th through March 4th, 2011. The conference provided a forum to present the latest results from analyses of experimental data (including space-borne, ground-based and co-ordinated data), simulation, and theory, addressing various aspects of the aurora. Presenters aimed to connect our knowledge of auroral morphology and mechanisms to candidate physical processes in the magnetosphere capable of powering and structuring the aurora on Earth and other planets. More details at:

This photo of the aurora was taken at the Poker Flat Research Range by James Spann during the conference week, featured on

"This is the first time I have seen the aurora borealis in person," says Spann who lives in Alabama. "It was fantastic--the greatest light show on Earth. It was cold (<20 F) outside but worth every minute of exposure and lost sleep. I am afraid now that I have been ruined for life since my first personal viewing of the aurora was so amazing."

As a researcher he also appreciated the greater meaning of the display: "This is the most obvious and accessible evidence of the connectivity that Earth has with our star the sun. Witnessing the connectivity first-hand was particularly special to me."

On-site organizing team (from left): Andreas Keiling, Fran Bagenal, Dave Knudsen, Dirk Lummerzheim, Masafumi Hirahara, Eric Donovan.

Keynote speaker: Syun Akasofu.

Attendee, Nataly Ozak, received a certificate during the banquet for seeing the aurora for the first time. She was one of more than 20 attendees, young and old, who had not seen the aurora (without an instrument) before coming to this Chapman conference. In the end, everybody who attended saw the aurora!

October 22, 2010:

ARTEMIS spacecraft commence operations:

highlights NASA's efficient use of the nation's space assets” said Dick Fisher, director of Helioiphysics Division in NASA's Science Mission Directorate.

See NASA press release 10-282:

The two Artemis spacecraft
commence science operations
in the lunar environment.

August 25, 2010:

Artemis Spacecraft First to Enter New Type of Orbit:

Congrats to the ARTEMIS mission operations and mission design team for a successful capture of P1 into the Lunar Lagrange point L2! This is a technical milestone, as this orbit has never been entered into by other spacecraft, and paves the way for planning of future missions that can use the orbit as a staging ground for lunar insertions, or for continuous data relay from the far side. The L2 entry of P1 will be followed by an L1 entry of P2 in October 2010, commencing the beginning of ARTEMIS science operations with 2 spacecraft.

See NASA press release at:

Illustration of ARTEMIS-P1 librations orbits

May 6, 2010:

Article in Der Spiegel on Recent THEMIS Findings:

Congratulations to Panov, Nakamura, Baumjohann and Glassmeier for a successful EGU press release, which took place on Monday, May 1st at EGU, on the topic of the interaction of flow bursts with inner magnetosphere pressure gradients. The interaction was found to cause a plasma recoil and ground pulsations. Their press conference resulted in several media publications including this one below (translated as "plasma bombs triggerspacequakes"), and brought our field to the front pages in Europe,

Article in Der Spiegel on the recent THEMIS findings (in German, click here for full article)

triggering space physics images in popular media, such as the aurora borealis over Iceland's Eyjafjallajokull (also see image below).

Aurora erupting over the active
Iceland volcano Eyjafjallajokull
in May 2010

February 26, 2010:

ARTEMIS P2 Completes Orbit Raise Maneuver Sequence:

As of February 26, 2010 the last orbit raise maneuver (ORM) of a long sequence was successfully executed on ARTEMIS P2 (THEMIS C), setting up this probe for a lunar flyby (on March 28), to initiate its trans-lunar trajectory (see image, left side). ARTEMIS P1 (THEMIS B) is already in its trans-lunar orbit, beyond 1,000,000 km from Earth (see image, upper right corner). At such large distances significant data recovery is impractical, so any data recovered on a best effort basis is primarily for the sake of checking health and status. This completes the period of ORMs successfully. Significant data recovery will commence again when the probes arrive at lunar distances starting in the fall, followed by capture into the Lissajous orbits. Hats off to the operations and mission design personnel for bringing the probes safely to this point!

ARTEMIS P2 completes orbit
raise maneuver sequence, shown
here en-route to trans-lunar

January 5, 2010:

THEMIS Paper by Zoltan Voros Makes Physics of Plasmas Cover:

Congratulations to Zoltan Voros for his THEMIS paper, titled "Evolution of kinklike fluctuations associated with ion pickup within reconnection outflows in the Earth's magnetotail" in Physics of Plasmas ( which made the cover page of that journal in December 2009!

December 17, 2009:

Colliding Auroras Produce an Explosion of Light, Report THEMIS Scientists:

This announcement by NASA/HQ and GSFC points to the work by Toshi Nishimura and Larry Lyons, which was reported today at the American Geophysical Union meeting in San Francisco. According to THEMIS project scientist Dave Sibeck of NASA's Goddard Space Flight Center, Greenbelt, MD, "By putting together data from ground-based cameras, ground-based radar, and the THEMIS spacecraft, we now have a nearly complete picture of what causes explosive auroral substorms." Lyons and Nishimura have identified a common sequence of events [during substorms]. It begins with a broad curtain of slow-moving auroras and a smaller knot of fast-moving auroras, initially far apart. The slow curtain quietly hangs in place, almost immobile, when the speedy knot rushes in from the north. The auroras collide and an eruption of light ensues. See full story at:
A fast-moving knot of auroras is poised to collide with a slower moving curtain hanging over the Arctic. THEMIS all-sky imagers photographed the collision on Feb 29, 2008.

November 19, 2009:

THEMIS Receives Accolades from its End of Prime Mission (EOPM) Review:

THEMIS completed its End Of Prime Mission (EOPM) review with high accolades from NASA/HQ and GSFC. The objective of the review was to demonstrate achievement of the prime mission science objectives, adherence to the mission Level-1 requirements, and report on overall mission technical performance. It gave us the opportunity to showcase the excellent science accomplishments and superb performance of the instruments and mission. HQ exclaimed how impressed they were with both the THEMIS science results and the THEMIS team's support of the community with data and with analysis tools. Congratulations to the team for such an exemplary performance.
THEMIS recently received accolades
in its EOPM review.

September 22, 2009:

HQ congratulates THEMIS Team on Successful Completion of Prime Mission; Wishes "Smooth Sailing" in Extended Phase:

In the aftermath of THEMIS's Science Working Team meeting on September 14-16 in Annapolis, MD (momento below), Jeff Heyes, Program Executive on our Mission Operations and Data Analysis, said: "Please convey to the team the NASA Heliophysics Division's sincere congratulations on the work that has been done on the THEMIS mission, getting it through the Prime phase of the mission, and on meeting the Full mission success criteria. We realize that it takes a great deal of dedication by all involved to make such an accomplishment. We look forward to continued success of the mission as it enters its extended phase."
Memento from THEMIS's Science Working Team meeting in Annapolis, MD on September 14-16, 2009.

July 20, 2009:

A Small Step for Artemis, a Giant Leap for NASA Heliophysics:

40 years after Apollo 11's lunar landing, NASA's first dual identical-satellite mission to study the Moon and its environment commences operations. Artemis consists of the pair of outer THEMIS/MIDEX probes which will be repositioned starting today and over the course of the next year and a half and will utilize the lunar gravity to gradually purturb their orbits and provide a low-thrust lunar orbit capture. Artemis stands for "Acceleration Reconnection and Turbulence and Electrodynamics of the Moon's Interaction with the Sun." The mission was approved in May 2008 as part of the extended operations plan of THEMIS by NASA's 2008 Heliophysics Senior Review panel [see]. Artemis (which also denotes the goddess of the moon and hunting in ancient mythology) will utilize simultaneous measurements of particles and electric and magnetic fields from two locations to provide the first three-dimensional information on how energetic particle acceleration takes place near the moon's orbit, in the distant magnetosphere and in the solar wind. It will also perform unprecedented observations of the refilling of the space environment behind the dark side of the moon, the greatest known vacuum in the solar system, by the solar wind.
Pictorial representation of ARTEMIS probes around the moon, as they will orbit in early 2011. ARTEMIS P1 and P2 are the outermost two THEMIS probes, which commenced their low-thrust lunar orbit insertion maneuvers on July 20, 2009, slated to arrive at the moon in October 2010.

June 5, 2009:

THEMIS-enabled Research on Chorus Waves Makes GRL Front Cover:

Congratulations to Wen Li for her GRL cover paper, titled: "Global distribution of whistler-mode chorus waves observed on the THEMIS spacecraft." Chorus waves are important for both electron acceleration and also electron scattering into the loss cone - therefore we are very interested in both understanding their generation, propagation and distribution, and incorporating their characteristics in radiation belt models for operational purposes. In the paper, Li et al show that chorus waves can persist at large distances (> 7 Re) in the dayside magnetosphere even during moderate or low geomagnetic activity - an observation that is enabled by THEMIS's unique orbit characteristics (12Re apogee) and comprehensive instrumentation. The observation leads to important clues regarding chorus generation by unstable drifting electron distributions. Li et al. also extend previous work regarding the occurence and amplitude of these waves at all local times (see ).
GRL front page cover featuring Li et al paper on THEMIS. Top: schematic of THEMIS orbits traversing the inner magnetosphere. Bottom: statistical distribution of chorus waves at low (left) and intermediate (right) latitudes.

May 25, 2009:

THEMIS Team Members Find Epicenter of Substorm Signatures:

THEMIS team members Jonathan Rae and Ian Mann (University of Alberta) announced today the breaking of new ground in pinpointing the epicenter of the arrival of substorm magnetic signatures from space to the ionosphere, using data from THEMIS's Ground-Based Observatories. Using methods akin to tracking seismological signal time delays, the magnetic signatures of a substorm in the ionosphere can, for the first time, be used to probe the eye of the space storm and represent a breakthrough in our ability to correlate ionospheric and magnetospheric signatures of substorm onset. As such they are expected to lead to significant advances in our ability to determine substorm onset time and location and advance our understanding of the substorm trigger and evolution under a variety of solar wind conditions. The findings were presented today at the 2009 AGU Spring meeting, and at a joint AGU/University of Alberta/CSA/NASA press conference (see

Image credit: Andy Kale, University of Alberta

May 8, 2009:

THEMIS Observes First Direct Link Between Chorus and Hiss Waves:

Observations obtained by THEMIS have provided the stongest evidence to date for the source of plasmaspheric hiss. In a paper by Bortnik et al., in today's issue of Science magazine, the first direct link between chorus and hiss waves has been demonstrated observationally. Hiss waves are important for space weather as they scatter radiation belt electrons into the loss cone. The waves throttle "killer electron" radiation amplitudes and are important to understand in order to better predict the consequences of large storms on spacecraft and humans in space. For details see: Science 8 May 2009, Vol. 324, no. 5928, pp. 775-778.

Simultaneous measurements at THEMIS D and E demonstrate that hiss waves in the plasmasphere orginate as chorus waves in a source region outside the plasmasphere. The chorus waves enter the plasmasphere directly (solid red lines), and evolve into hiss (dashed copper lines) by bouncing back and forth between the northern and southern magnetic poles. View larger figure.
Image credit: NASA/SVS and J. Bortnik

April 23, 2009:

THEMIS Observations Reveal Presence of Vortical Structures:

Observations by THEMIS in the nightside magnetosphere revealed the presense of vortical structures responsible for hundreds of thousands of Amps of electrical current flowing into Earth's ionosphere and producing spectacular auroral swirls. The results were reported by Andreas Keiling, Karl Heinz Glassmeier and Olaf Amm at today's Spring EGU meeting, in Vienna, Austria.

View larger figure.
Image credit: A. Keiling et al., THEMIS/NASA

April 17, 2009:

THEMIS Mission in Dusk Sector:

The mission is now in the Dusk sector collecting data from a unique vantage point: Probes are separated by 1-3 Re and as of April 24th they will collect time-based survey data and time-based particle bursts and wave bursts, so that waves can be correlated at high resolution between widely separated regions of space. The outer probes are already collecting magnetopause and shock crossings bursting on density triggers.

March 20, 2009:

THEMIS Accomplishes Baseline Objectives, Survives Deep Shadow:

THEMIS has now fully accomplished its baseline objectives by completing the full second year's worth of magnetotail observations. Despite the extended Solar Minimum, solar wind energy coupling was strong and frequent enough to enable observations of at least two dozen substorms. THEMIS P1 and P2's tail orbits were changed in order to increase current sheet encounters, with excellent results in the data. In addition, there have been 3sec resolution full angular distributions of electrons 12hrs per orbit on P1 and P2 in the tail season for ~3weeks, while P3,4,5 stayed in that mode since mid-February. The resulting data recovery from all probes is about twice what we initially promised. The scientific potential of the dataset is astounding.

Furthermore, P1 has gone through the longest shadow any of the probes will ever encounter. It was a 4-hour shadow (above the 3-hr design limit) that resulted in no loss of data (other than the precautionary turn-off of the High Voltage power supply for the ESA instrument). All probes are undergoing smaller eclipses (you can spot them in the overview plots from the rotation of the magnetic field due to spacecraft moment of inertia changes and lack of sun pulse information).

February 27, 2009:

Road Cleared for ARTEMIS Mission Implementation:

On Feb 24, 2009 ARTEMIS passed its mini-Confirmation review at GSFC. Therefore, the road has been cleared for the upcoming mission implementation. There will be a delta (pico) review in early May to ensure progress with contingency planning is adequate, but we don't anticipate any problems. Congratulations to the implementation teams at UCB, JPL and GSFC for their outstanding progress to-date!

The essence of the comments of the review board was that the ARTEMIS team has done an outstanding job, especially considering the little (8 months) time that has passed since the Senior Review go-ahead. Of course, it was recognized that there is still a lot of work ahead, but the team yesterday presented a reasonable, viable plan, which conveys confidence they can deliver. Even though this is a challenging project, given the resources and time available, this condition was deemed acceptable considering that the THEMIS probes are already operating well and this is an extended-phase mission. The reviewers have come up with less than a handful of requests for action, which I am certain will strengthen the project, as it moves towards the Orbit Raise Maneuvers in the upcoming summer. Tentatively the ORMs start July 9th.

THEMIS P1 (TH-B) in red and P2 (TH-C) orbit between this summer's orbit raise maneuvers and October 2010 when they will capture the Lagrange points between Earth and Moon. After six months in those orbits, P1 and P2 will be inserted into Lunar orbits where they will make measurements of the Lunar warke, the magnetotail, and the solar wind through September 2012. View larger figure.

February 11, 2009:

THEMIS-B and -C Observed by Asteroid Hunters:

Proof that THEMIS has actually launched:

Looking for asteroids that may be on collision course with Earth, Peter Birthwhistle in the UK and Bill J. Gray in the US have spotted THEMIS B (pictures to the right) and THEMIS C. Asteroid hunters are used to detecting satellites amongst their real quarry, but most satellites move so fast that astronomers can immediately discount them as "obvious" man-made objects. At apogee, though, THEMIS-B and -C appear to be moving slowly enough so that they can look like a real asteroid (until you get enough data to make it clear that they are close in and orbiting Earth). Birthwhistle and Gray took the most recent THEMIS-B images from the Mount Lemmon Survey telescope in Arizona. Fitting those data, they derived the THEMIS-B orbital elements in the time interval between THEMIS maneuvers. The left image shows a superposition of sky pictures with THEMIS-B in the center using the derived THEMIS-B elements, for February 6, 2009. The dot in the middle is THEMIS-B! The same process after the THEMIS-B T2-28d "tweak" maneuver resulted in the right image on February 19 (again THEMIS-B is the dot in the center). Stars move in relation to THEMIS and appear as dot-streaks. The images were taken at the Great Shefford Observatory in the UK. These results are welcome for THEMIS scientists, who can now rest assured that recent reports on tail reconnection have used data collected by actual probes in space.

For more information: Images of THEMIS-B taken by Peter Birthwhistle and Bill Gray at the Great Shefford Observatory in the UK. The tiny white dots in the middle of the images represent THEMIS-B. The white dot-streaks are stars moving in relation to THEMIS.

December, 2008:

THEMIS Scientists Discover Breach in Earth's Magnetosphere:

December 16, 2008
Earth's magnetic field deflects highly charged particles emitted by the sun, known as solar wind, which speed towards Earth at a million miles per hour. However, these particles are not fully deflected by the magnetosphere, but instead penetrate through two areas. The extent to which these breaches allow solar wind particles to enter through the magnetopshere is dependent on the orientation of the sun's magnetic field. Previously, it was thought that when the sun's magnetic field aligned with that of Earth, the transfer of solar wind particles into Earth's magnetosphere was minimal. However, THEMIS team scientists recently discovered that contrary to longstanding views on how and when solar plasma enters the Earth's magnetosphere, 20 times more solar wind plasma penetrates Earth's magnetosphere when the sun's magnetic field is aligned with that of the Earth.

  • View the NASA press release.

  • Read more in this THEMIS nugget.

  • THEMIS Enters Second Tail Season:

    As of December 15, 2008, THEMIS has entered its second tail season: the probes have started to line up in the tail and burst on Bz (Particle Bursts) and Filterbank data (Wave Bursts). P2, P3, P4 and P5 have already captured the first substorm of the new season, on December 15, 09:15UT (precursor) and 09:40UT (onset), with the probes were in minor conjunction (P1 in the sheath). Four-day conjunctions occured on December 17th and will occur every 4 days thereafter through mid-March, between 00:30-12:30 UT. Note that P5 is below P3 and P4.

    October, 2008:

    Successful Completion of Plane-Change Maneuver on THEMIS-B (P1):

    On Friday, October 16th, a large orbit plane-change maneuver on THEMIS-B (P1) was completed successfully. The plane-change maneuver was followed by an attitude adjustment, bringing P1 to its nominal science attitude. The plane-change maneuver consumed almost as much fuel as the combined fuel of all previous maneuvers on P1; it was a nearly continuous 100-minute burn of both the axial thrusters. The resultant >20deg plane change reversed the cumulative effect of lunar perturbations over the last year and put P1 in an excellent position to perform high-quality night-time near-neutral sheet observations in the second tail season. The orbit was optimized to achieve prolonged neutral sheet residence within 1Re. You can find predicted orbits (based on plans from a month ago) at New predicted elements will appear there shortly.

    A similar, though smaller maneuver on TH-C (P2) will take place during the early morning hours of Wednesday, October 22nd. We look forward to an exciting second tail season ahead!

    Our thanks go to Manfred Bester and to the entire mission operations team at UCB for an impeccable execution of a demanding maneuver plan, involving working through some tough hours over the last few days; as well as to the orbit designer Sabine Frey for her careful orbit analysis and optimization.

    September, 2008:

    THEMIS Completes Data Collection Requirements for Dayside Observations:

    As of Wednesday, August 28th, THEMIS has completed its data collection requirements for dayside observations. The five THEMIS probes are now in the dawn portion of the dayside phase. They have collected more than 200 hrs of 4 probe dayside conjunctions, and more than 100 hours of 5-probe alignments. Many of those conjunctions are from the unique vantage point of simultaneous solar wind, foreshocked solar wind, and magnetopause encounters. Owing to the slow dynamic pressure of the solar wind in the last 2 months, most of the inner probe magnetopause encounters are within 3 weeks of August 4th, near the subsolar point. We expect more flank magnetopause encounters in the 2nd dayside season next summer.

    July, 2008:

    THEMIS Observations Show that Magnetic Reconnection Triggered Substorm Onset:

    THEMIS captured several substorms from a unique vantage point, showing that magnetic reconnection triggered substorm onset. Results appeared in Highlights of Science Express on July 24, 2008 and on the cover of the August 15, 2008 issue of the magazine.

    Read the article>>

    May, 2008:

    ARTEMIS Mission Approved by NASA:

    NASA has extended the THEMIS mission to the year 2012. In addition, ARTEMIS, a new mission that will take the two outer THEMIS probes into lunar orbits and perform solar wind, magnetotail, and lunar science, has been provisionally approved by NASA, pending a technical review before February 2009. Excerpt from the senior review report: "The senior review panel congratulates the THEMIS science team on their innovative plan to drastically reposition the five THEMIS probes at the conclusion of the prime THEMIS mission. The extended mission, which will consist of THEMIS-Low and the lunar-orbitting ARTEMIS, is highly compelling, both for the individual scientific goals and what will undoubtedly be their excellent contributions to the Helio-Physics Great Observatory." ARTEMIS will perform measurements in the lunar environment from October 2010 until September 2012.

    Please find the extended THEMIS proposal here.
    Please find the Senior Review report here.

    THEMIS Receives NASA Group Achievement Award:

    On Thursday, May 8th, NASA Administrator Michael Griffin bestowed upon the THEMIS team a Group Achievement Award for the successful delivery, launch, and operations of the THEMIS probes. NASA chief engineer Chris Scolese praised the THEMIS team for its tenacity and ingenuity. The award comes at an important juncture between achieving minimum mission science and ramping up science productivity. In addition, on May 13th, THEMIS received a Goddard Space Flight Center Group Achievement Award.

    April, 2008:

    THEMIS Completes 1st Tail Season:

    THEMIS accomplished ~200 hours of four-probe conjunction and caught in excess of five dozen substorms, a dozen of which were from a pristine vantage point within the meridian. Many of those are being presented at the 9th International Conference on Substorms (ICS-9) in Graz, Austria, from May 5-9, and will form the basis of further studies and presentations during the summer.

    February, 2008:

    Mission Milestone:

    As of the end of February, THEMIS has observed 154 hours of four- probe conjunctions (the requirement was 94 hours), during which it observed 57 substorms. Of these 57 substorms, about 6-10 were observed from an excellent vantage point during the period Feb02-Feb26. Major findings will be presented at the International Conference on Substorms in Graz, Austria and at the Fall AGU meeting in San Francisco. Preliminary results will be presented at the Spring AGU meeting in Fort Lauderdale. So far, the magentotail looks far more interesting than ever before.

    January, 2008:

    Constellation Status:

    EFI deployment operations for the entire constellation were completed on 14 January 2008 with the deployment of THEMIS-A axial booms. This followed the deployment of THEMIS-A spin planes booms the previous week. In total, the EFI had nominal deploys of 20 wire boom and 10 stacer boom systems.

    November, 2007:

    Constellation Status:

    With the final EFI deployment of Probe P1 (THEMIS B), the constellation is now fully configured, checked out, and ready to start tail season operations. The EFI deployment for THEMIS B (P1) was achieved in 3 work days, spread out over 2 orbits (8 days). All boom deploy and spin-up activities were nominal with characteristics very close to those observed during the deploy of THEMIS C-E (P2-P4).

    October, 2007:

    Constellation Status:

    On October 12th P1 (TH-B) was placed in its final, 31Re apogee orbit. This completed the bulk of maneuvers for P1 (minor tweak maneuvers to be continued throughout the mission). Both P1(THB) and P2(THC) are now pointing on ecliptic-science-south, i.e., roughly normal to the ecliptic but 8deg away from the Sun (computed for early February 2007). The inner three, P3(TH-D), P4(TH-E), P5(TH-A) are expected to continue to be targeting an ecliptic-science-north attitude (8deg towards the Sun for early February 2007). The reason for this 8deg angle is to permit good quality EFI measurements (avoids sphere shadowing and ensures a large angle between the nominal magnetic field and the spin plane which allows robust computation of E along the spin axis from the E*B=0 approximation). More data is expecting to be flowing down soon given this new attitude; software uploads, instrument configurations, and burst triggers are expected to also be finalized in the next 2 months.

    August 16 - September 3, 2007:

    Constellation Status:

    The THEMIS constellation continues to operate nominally and is in a very good state of health. No anomalies were encountered since the release of the most recent, formal Mission Operations Report (No. 16). All instruments are turned on and are collecting science data.

    Summary of Recent Activities:

    • The THEMIS mission has successfully completed the Coast Phase science operations that officially lasted for two months (July 1 - August 31, 2007).
    • All five probes underwent attitude precession maneuvers - THEMIS A and D on August 31, DOY 243, and THEMIS B, C and E on September 1, DOY 244 - in preparation of the upcoming, first axial thruster firings. All attitude maneuvers achieved their goals. Post-maneuver processing as well as orbit and attitude determination are in progress to provide the baseline Probe states for the final Mission Design run prior to the first set of orbit maneuvers.

    August 9 - August 15, 2007:

    Constellation Status:

    The THEMIS constellation continues to function very well. All five probes are currently in 31.3 hour coast phase orbits with their spin axis pointing towards the ecliptic north pole with a +8 deg tilt towards the ecliptic longitude of the Sun on February 7th, 2008. All instruments are powered on and continue to function well and are collecting science The EFI spin-plane and axial booms are completely deployed on THEMIS C (P2), D (P3), and E (P4), while those on THEMIS B (P1) and A (P5) will remain stowed until their mission orbit placement is completed.

    Summary of Recent Activities:

    • IDPU Flight software version 0x47 was uploaded to RAM on THEMIS on A, B, and D
    • Cold reset recovery on THEMIS E

    August 2 - August 8, 2007:

    Constellation Status:

    The THEMIS constellation continues to function very well. All five probes are currently in 31.3 hour coast phase orbits with their spin axis pointing towards the ecliptic north pole with a +8 deg tilt towards the ecliptic longitude of the Sun on February 7th, 2008. All instruments are powered on and continue to function well and are collecting science The EFI spin-plane and axial booms are completely deployed on THEMIS C (P2), D (P3), and E (P4), while those on THEMIS B (P1) and A (P5) will remain stowed until their mission orbit placement is completed.

    Summary of Recent Activities:

    • BEB table revision F and IDPU script set 0004 version 6 upload to THEMIS A-E
    • ETC table version 7 upload to EEPROM on THEMIS B-E
    • RTS59 upload to THEMIS A-E

    July 26 - August 1, 2007:

    Constellation Status:

    The THEMIS constellation continues to function very well. All five probes are currently in 31.3 hour coast phase orbits with their spin axis pointing towards the ecliptic north pole with a +8 deg tilt towards the ecliptic longitude of the Sun on February 7th, 2008. All instruments are powered on and continue to function well and are collecting science The EFI spin-plane and axial booms are completely deployed on THEMIS C (P2), D (P3), and E (P4), while those on THEMIS B (P1) and A (P5) will remain stowed until their mission orbit placement is completed.

    Summary of Activities:

    • Reconfiguration of Burst Memory on THEMIS C
    • ESA MCP Electron HV change on THEMIS A, B and E
    • ESA MCP gain toggle test on all probes
    • ETC version 7 table load to EEPROM on THEMIS A

    July 19-25, 2007:

    Constellation Status:

    The THEMIS constellation continues to function very well. All five probes are currently in 31.3 hour coast phase orbits with their spin axis pointing towards the ecliptic north pole with a +8 deg tilt towards the ecliptic longitude of the Sun on February 7th, 2008. All instruments are powered on and continue to function well and are collecting science The EFI spin-plane and axial booms are completely deployed on THEMIS C (P2), D (P3), and E (P4), while those on THEMIS B (P1) and A (P5) will remain stowed until their mission orbit placement is completed.

    Summary of Activities:

    • EFI sensor optimization on THEMIS C, D, and E
    • ESA MCP gain toggle tests on THEMIS A and E
    • SSR power cycle on THEMIS E
    • Testing of various instrument control and data acquisition modes via ATS loads

    June 28 - July 18, 2007:

    Constellation Status:

    The THEMIS constellation continues to function very well. All five probes are currently in 31.3 hour coast phase orbits with their spin axis pointing towards the ecliptic north pole with a +8 deg tilt towards the ecliptic longitude of the Sun on February 7th, 2008. All instruments are powered on and continue to function well and are collecting science The EFI spin-plane and axial booms are completely deployed on THEMIS C (P2), D (P3), and E (P4), while those on THEMIS B (P1) and A (P5) will remain stowed until their mission orbit placement is completed.

    June 7, 2007:

    Constellation Status:

    The THEMIS constellation continues to operate nominally and is in a very good state of health. No anomalies were encountered. All instruments are turned on and are collecting science data. As of this morning, three probes - THEMIS C, D and E - have their Electric Field Instruments completely deployed, and all EFI sensors are working nominally. The EFI booms on THEMIS B (P1) and THEMIS A (P5) will be deployed after their mission orbit placement is completed in late 2007 and early 2008, respectively. All stored science and engineering data are recovered regularly with a success rate of nearly 100% across the constellation. The THEMIS ground systems continue to function very well.

    May 15th, 2007:

    Constellation Status:

    The THEMIS constellation continues to operate nominally and is in a very good state of health. All instruments are turned on and are collecting science data. All stored science and engineering data are recovered regularly with a success rate of nearly 100% across the constellation.

    Recent Events:

    Completed EFI deployment steps 0-12 on THEMIS C (see URL listed below). Please note that the deployment sequence was optimized and now only requires 14 steps (0-13). The only remaining step for this probe is the axial boom release (step 13) which is scheduled for later this week.

    The EFI spin-plane boom deployment went very smooth - there were no issues with dynamic stability during the deployment or following spin-up maneuvers. The dual pulse spin-up procedure worked very well. According to the EFI team, the instrument generates science data with excellent quality.

    Completed all required orbit maneuvers for the coast phase placement of THEMIS A, B and D.

    May 14th, 2007:

    Constellation Status:

    The THEMIS constellation continues to operate nominally and is in a very good state of health. All instruments are turned on and are collecting science data.

    Occasional hang-ups of the ETC FPGA that controls data acquisition from the SSTs and ESAs were observed again on multiple probes. The FPGA was successfully reset on these probes. A work-around is still tested on FlatSat. No other anomalies were encountered.

    Recent Events:

    Ran science-like orbits on all five probes.

    Uploaded new IDPU FSW Version 0x43 (patch) to all five probes which fixes two issues (data compression and time tagging of FGM data). Data compression was successfully exercised on THEMIS D. FGM data are now time-tagged correctly on all five probes, improving attitude determination with MSASS significantly.

    Started final EFI commissioning phase (steps 0-2) on THEMIS C (P2). On DOY 129 (March 9) the probe was spun up to 20 rpm, the EFI X and Y spin-plane boom doors were opened, and the X and Y axis booms were deployed by 5m each. The observed spin rate change during the deployment was nominal. The EFI Scientist reported nominal sensor operation.

    Plans for Upcoming Weeks:

    Continue with: EFI commissioning steps 3-15 on THEMIS C and orbit placement for the coast phase.

    Deploy EFI booms on THEMIS D and E.

    Test: data compression on probes THEMIS A, B, C and E; control of science data acquisition via instrument triggers.

    Please refer to THEMIS Mission Operations Report No. 6 for additional reference material. Report No. 7 will cover DOY 113-127 (April 23 - May 7) and should be released by the end of this week.

    May 2nd, 2007:

    Constellation Status:

    The THEMIS constellation continues to operate nominally and is in a very good state of health. All instruments are turned on and are collecting science data. No anomalies were encountered.

    Events of Last Week:

    Performed attitude precession maneuver to science north on THEMIS A-D, using axial thruster A2. All 20 thruster across the constellation have now been exercised and function nominally.

    Performed spin-up maneuver to 20 rpm on THEMIS A and B, using the dual-pulse-per-spin thrusting technique with tangential thruster T1. This mode is required to be used for all spin-up maneuvers to maintain dynamic stability of the probes, once EFI spin-plane boom deployment has started.

    Uploaded IDPU FSW patch 0x43, new IDPU script set 0004 and ETC Table Checker program to THEMIS C

    Plans for Upcoming Weeks:

    Per agreement, GSFC/FDF will reduce back-up orbit determination to one OD solution per probe per month on DOY 120 until the mission orbit placement begins in fall. UCB/FDC continues to generate OD solutions for all probes typically 2-3 times per week, and continues to deliver tracking data to FDF for each pass.

    Upload IDPU FSW patch 0x43 to THEMIS D and E (DOY 120) Select ESA mode "Shocked Solar Wind" on THEMIS E

    Upload IDPU FSW patch 0x43 to THEMIS A and B (DOY 123) Enable data compression on THEMIS D

    Repeat FGM commissioning procedure on all probes near apogee (per request of FGM team)

    Run science-like orbits on all probes

    Perform perigee raise maneuver on THEMIS E (DOY 129)

    Perform EFI deployement on THEMIS C over 6 orbits (DOY 129-136) Detailed plans will be finalized during the upcoming week.

    Please refer to THEMIS Mission Operations Report No. 6 for additional reference material.

    Report No. 7 will cover DOY 113-127 (April 23 - May 7).

    March 29th-April 6th, 2007:

    Current Constellation Status:

    All five probes are safe and healthy, and are in stable orbits. The attitudes are nearly ecliptic normal. All science instruments are operational and are collecting data.

    Please refer to the THEMIS Constellation Status web page for detailed, current status information (see below).

    A preliminary orbit placement decision was made on March 27:

      • THEMIS A -> P5 Orbit
      • THEMIS B -> P1 Orbit
      • THEMIS C -> P2 Orbit
      • THEMIS D -> P3 Orbit
      • THEMIS E -> P4 Orbit

    The mission orbit placement will begin in late August, and will be completed in preparation of the first winter observing season "Tail 1" when the probe orbits will be aligned with the Earth's magneto tail. Meanwhile, all five probes are maintained in temporary "coast phase" orbits.

    Following the launch dispersion, the five probes ended up in nearly identical orbits where C is leading and E trailing the group D-B-A with differential orbital periods of -/+ 5 min, respectively:


    The desired configuration for the coast phase is as follows:


    Based on the probe placement decision, THEMIS C, D and E will have their EFI booms deployed early (see below), and should ideally be at the center of the coast phase constellation at apogee.

    Recently Completed Tasks:

    Performed perigee raise maneuvers with each probe to control the differential precession of the argument of perigee amongst the five probe orbits and to calibrate the thrusters:

    DOY 87: THEMIS C perigee raise by 25 km to 585 km (delta V 1.3 m/s)

    DOY 88: THEMIS A perigee raise by 70 km to 652 km (delta V 3.6 m/s) THEMIS D perigee raise by 70 km to 660 km (delta V 3.4 m/s) THEMIS E perigee raise by 70 km to 656 km (delta V 3.6 m/s)

    DOY 93: THEMIS B perigee raise by 70 km to 691 km (delta V 3.6 m/s)

    DOY 94: THEMIS C perigee raise by 70 km to 705 km (delta V 3.5 m/s)


    Performed the first of a series of additional orbit maneuvers to position the five probes for the coast phase:

    DOY 95: THEMIS D perigee raise by 363 km to 1050 km (delta V 20.9 m/s)

    All delta V maneuvers were accomplished in side thrust mode, using the two tangential thrusters with a 60 deg thrust angle at a spin rate of approximately 20 rpm. Small attitude and spin rate changes were encountered as an undesired, but unavoidable byproduct of the side thrust maneuvers. These changes will be corrected later.

    Performed post-maneuver operations, including maneuver reconstruction and calibration, orbit and attitude determination.

    Refined mission trajectory design for the coast phase, based on inputs from the PI and the science team.

    Completed various science-like orbits to test data acquisition modes.

    Ongoing Activities:

    All pass activities are conducted with FOT on console. Passes are currently still taken in blind acquisition mode, allowing a high degree of operational flexibility for re-planning.

    ATS loads are used primarily to reconfigure instruments in various orbit regions and to support maneuver operations.

    Characterization of instruments in science-like orbits. A dedicated 'fields' orbit for all five probes will start on DOY 98.

    Telemetry recovery, archiving, processing and data trending.

    Communications tests with BGS, using BPSK at the lowest six data rates to assess potential gains in link margin at large ranges.

    Investigation of various anomalies.

    Upcoming Tasks:

    Maneuver operations for the coast phase orbit placement:

    All probes will perform additional apogee and/or perigee change maneuvers over the course of the next few months to achieve and maintain the coast phase constellation. The maneuver sequence is designed such that minimum fuel is consumed and virtually all of the perigee and apogee changes count towards the mission orbit placement.

    EFI boom deployment on 3 probes (THEMIS C, D and E):

    THEMIS D (P3) will begin with the EFI boom deployment on DOY 106 (April 16). The entire sequence alternates between boom deployment steps, instrument test and calibration runs, and data recovery near perigee; this takes 6 orbits (8 days) to complete.

    The EFI boom deployment sequences for THEMIS C (P2) and E (P4) will be interleaved and are currently scheduled to begin on DOY 128 (May 8).

    Note that the EFI booms for THEMIS A (P5) and B (P1) will be deployed after their mission orbit placement is completed. These two probes require the largest fuel usage for their orbit placement. Delaying the boom deployment will allow for a rapid ascent of THEMIS B to the P1 orbit by using efficient attitude precession maneuvers and axial thruster burns for the delta V maneuvers. THEMIS A (P5) is the designated on-orbit spare and will have its EFI booms deployed, once THEMIS B (P1) has completed its orbit placement. The other three probes will perform their mission orbit placement using the tangential thrusters in "side thrust mode".

    March 14th, 2007: In the past day, we performed telecom tests at apogee with all probes and multiple ground stations.  These were very successful showing us the probes can telemeter at 64 K bits per second to Berkeley throughout this orbit. Probe C and D SSTs were turned on again and left running in order to get a measurement with no ESA High Voltage sweeps.  Probe E SST was reconfigured.  Probe B ESA ions and electrons were brought up in High Voltage.

    At the present time, ESA HV is running on A and B, while SST is up and running on C and D.  Science data is being collected and returned successfully in Slow Survey mode. Assuming data looks good overnight, we'll raise ESA High Voltage on C, D and E while turning on SST A, B and E.  That would complete the initial commissioning on all instruments.

    March 12th, 2007: Today, ESA electron High Voltages were checked out on probes A, B, D and E. Each was ramped up successfully to full voltage and all four performed beautifully.  Probe C ESA was not ramped up because of the ongoing set up issue with the ESA/SST controller.  We plan to get back to that probe tomorrow.

    March 11th, 2007: Today, the SST on Probe C was powered up again in order to check out the sun-blanking circuitry.  Currents looked good and stable, but the expected packet telemetry was not coming through.  Once again, SST was turned off while engineers worked on an updated plan for SST.

    All probes are in good health and their orbits are well known.

    March 10th, 2007: Today, ESA ion High Voltages were checked out on all five probes. Each was ramped up successfully to full voltage and all five performed perfectly.  Probe A ESA was intentionally left at high voltage while the other probe ESAs were ramped down for the time being. The science team reports nominal performance from all five ESAs, and excellent science data quality from the THEMIS A Ion detector.

    All probes are in good health and their orbits are well known

    March 8th, 2007: Today, SSTs on Probes B and C were turned on and their attenuators were exercised.  Probe D's SST was not commissioned since the SSR was still full from ESAs commissioning yesterday.  Probe A and E SSTs were turned on, but due to sun in their apertures at these attitudes, their currents red-limited and they were turned off before the end of their contacts. By the end of the day, all SSTs were powered off in order to allow manevers to proceed.

    Probes A, E, D and B were maneuvered to ecliptic normal, enabling better communications, stable power and thermal conditions.  Fuel usage since launch has been a mere 0.2 kg.

    Science and engineering data for all probes was played out.  All probes remain in good health and their orbits are well known.

    March 7th, 2007: Today, all ESA covers were successfully opened using their primary actuators. Each ESA was tested with its internal test pulser and all ESAs performed well. Later this week we will turn on the High Voltage to the ions and electrons.

    March 5th, 2007: Today, we aborted planned maneuvers on Probes A, D and E due to poor link margin.  The probes were over 87000 km range and could not sustain RF link to the BGS antenna. We are replanning these maneuvers for later in the week, while proceeding ahead with the commissioning in the current attitude.

    All five probes remain in excellent health, with the Fluxgate, Search Coil, Electric Field and ESA Low Voltage on.

    March 4th, 2007: Over the weekend, Probes B and C were maneuvered so that their antennae were north-south with respect to the ecliptic.  While both maneuvers were successful in general, Probe B's maneuver on Saturday resulted in a side tilt of 40+ degrees to the ecliptic plane.  This was confirmed when the Probe passed through perigee and its FGM data showed the tilt.

    Probe C's maneuver sequence was modified to include newly determined information about the probes, so C's maneuver on Sunday was picture perfect. 

    Probes A, D and E will be maneuvered to ecliptic normal in the early morning of Mar 6 and, assuming those maneuvers go well,  Probe B will be tipped up on Mar 7.

    All five probes remain in excellent health, with the Fluxgate, Search Coil, Electric Field and ESA Low Voltage on.

    February 27th, 2007: Today, Probes D and E were spun up to 20 RPM following their magnetometer boom deployments yesterday.  All probes continue taking magnetic data in preparation for a maneuver to ecliptic normal attitude. 

    The planned maneuvers to ecliptic normal will be performed in steps, where Probes B & C will maneuver on Friday and Probes D, A & E will maneuver on Saturday.  This allows science data to be recovered in an unusual mixed configuration; ie. two probes rotated with respect to the other three.

    All five probes remain in excellent health, with the Fluxgate, Search Coil, Electric Field and ESA Low Voltage on.

    February 26th, 2007: Today, Probes A, B and C were spun up to 20 RPM following their magnetometer boom deployments over the weekend.  Probes D and E had their magnetometer booms deployed.  All probes are taking magnetic data in preparation for a maneuver to ecliptic normal attitude at the end of the week.

    All five probes remain in excellent health, with the Fluxgate, Search Coil, Electric Field and ESA Low Voltage on.

    February 24th, 2007: The last 24 hours have seen an amazing amount of accomplishments on the five probes. All five EFI and SCM instruments were turned on, a calibration of Probe B FGM was performed, and all probes were spun down to 11 RPM.  We recovered all engineering and science data from all probes, too.
    As the probes have begun to separate a little, we were also able to contact three probes simultaneously using three different ground stations.  Probes E, D and C telemetered to Berkeley, Santiago and Wallops at 512, 256 and 128 kbps, and the data routing network worked perfectly.  Of the 20 passes during the day, Berkeley had 13, Santiago 1, Haartebeestok 1 and Wallops had 5 tracking passes.
    All five probes remain in excellent health.  Temperatures are very mild on the probes now in their nominal attitude with sun on their side panels. 

    February 23rd, 2007: Today, Probes C and B EFI and SCM instruments were turned on and Probe B FGM calibration performed at mid-range.  All systems were nominal in current and temperature.  The first THEMIS instrument data for EFI and SCM data were played out and looked nominal.
    All five probes were de-spun from their initial spin rate of 16-17 RPM down to 11 RPM, in preparation for the upcoming magnetometer boom deployment. This involved firing the radial thrusters for 6 to 7.5 seconds depending upon the initial spin rate.  As we expected, each spacecraft wobbled a bit, but telemetry and commanding were unaffected.
    All five probes remain in excellent health.  Temperatures are very mild on the probes now in their nominal attitude with sun on their side panels.  Engineers are continuing data collection and analysis on two technical items. The first item involves the occasional false over-voltage trips in charging circuits and the second involves measuring the command and telemetry link performance.  There were no over-voltage-trips today.
    Communications with the probes have been very successful with Berkeley Ground Station but not yet with Wallops.  Last night we had successful telemetry at 64 KHz at a distance of over 70000 km using Probe B yet we were unable to lock on RF carrier with Wallops just moments earlier.

    February 22, 2007: Today, on all Probes the Instrument Data Processors, FluxGate Magnetometers and ESA Low Voltage Power Supplies were turned on and checked out. All systems were nominal in current and temperature. FGM sensor data recording began and we should see the first science data play out in the next orbit.

    Probe A was rolled so that the sun is on its side-panels rather than on its top. This will cool the top down.

    All five probes are in very good health. Temperatures are very mild on the probes now in their nominal attitude with sun on their side panels. Engineers are finalizing data collection and analysis on two technical items at this time. The first item involved the occasional false over-voltage trips in charging circuits and the second involved measuring the command and telemetry link performance.

    Communications with the probes have improved greatly due to better orbit and attitude information. For example, last night we had successful telemetry at 64 KHz at a distance of over 50000 km using Probe A

    February 21st, 2007: Today, THEMIS Probes B, C, D and E were successfully maneuvered 33 degrees as planned to have sun on their side solar arrays. Each maneuver took about 2.5 minutes while each probe fired 40 pulses on one of the axial thrusters in phase with the spin. This attitude provides better temperatures around the probes as well as better communication to the ground. By plan, Probe A was left in the launch attitude for one half orbit until we contact it one more time with TDRS. After that time, Probe A will be rolled to the same attitude as the other four.

    All five probes are in very good health, but the team is currently working two technical items at this time, one regarding occasional false over-voltage trips in charging circuits and the second involves measuring the command and telemetry link performance.

    First, the occasional false over-voltage-protection trips are essentially due to the fact that the the batteries are fully charged. Small noise on the battery readings have caused the circuits to occasionally think that the battery is too full. In response, the circuits shunt power for a few minutes until the battery voltage is a fraction lower. It has become apparent that the solar arrays are putting out more power than projected, and that the shunts are barely able to regulate. Thus, we have turned on additional heaters to balance the energy in the probe.

    Second, initial poor communications with the probes is to a large extent due to a shorter than predicted orbit. The orbits are now 1.073 x 14.697 Re at 15.9 degrees. As we have learned how to point the antenna better, communications at high data rates are a regular occurrence. Still, we've noticed that Charlie and Bravo have the best performance while the other three have 2-5 dB dips in their signals at certain orientations. These dips may be due to the un-deployed magnetometer booms on the top of the spacecraft and may go away when we deploy them Sunday 2/25/07.

    February 17th, 2007: NASA's THEMIS mission successfully launched at 6:01 p.m. EST from Pad 17-B at Cape Canaveral Air Force Station, Florida. All trajectories appeared right on target. First contact at the Berkeley Ground Station was successful.

    Watch the launch video.

    January 29th, 2007: Today the THEMIS spacecraft will be mated to the 3rd stage of the rocket. You can get video of this by clicking on the link "AE Video 1 Streaming Feed" at the following URL:

    January 26th, 2007: THEMIS will be launched from the same Pad as STEREO. Jetty Park is 2.9 miles from the pad and is apparently closer than the official site. Visit this website for information about launch viewing: Where & How to Watch Delta 2 Launches.

    January 24th, 2007: THEMIS passed its Mission Readiness Board review yesterday. The NASA Associate Administrator for the Science Mission Directorate, Mary Cleave, stated that the mission is a pathfinder for future Heliospheric constellations and thanked the team for its efforts in making it possible for the entire community. Deputy AA Colleen Hartman stated that this is a scientifically very exciting mission and that she felt really fortunate to see it through end-to-end in her term. Dick Fisher, Heliophysics Division director, stated that the team performance in general and in this review in particular, sets a very high standard for missions to come.