2024 THEMIS SCIENCE NUGGETS
Global Observations of Geomagnetically Induced Currents Caused by an Extremely Intense Density Pulse During a Coronal Mass Ejection
Terry Z. Liu
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles
Introduction
Geomagnetically induced currents (GIC) in power systems are among the most severe space weather hazards, yet the mechanisms driving large GIC events are not well understood. To tackle this challenge, we performed multiple-spacecraft observations in conjunction with ground magnetometers and GIC measurements distributed around the world.
Results
On April 23-24, 2023, a coronal mass ejection (CME) triggered a significant geomagnetic storm. Within the magnetic cloud region of the CME, ARTEMIS observed a global-scale density pulse lasting 10–20 minutes with a compression ratio of ~10 (Figure 1a). As the density pulse approached Earth, its intense dynamic pressure caused dramatic back-and-forth motion of the bow shock and the magnetopause, by approximately 6 RE and 2 RE, respectively, observed by THEMIS and KOMPSAT spacecraft (Figures 1b-1d).
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| Figure 1. THEMIS observations and ground response to the upstream magnetic bottle structure. From top to bottom are (a) THC dynamic pressure, (b) THE dynamic pressure, (c) THE total magnetic field (Bt, blue line) and the northward component (Bz, black line) in GSM coordinates, (d) KOMPSAT total magnetic field (Bt, blue line) and the northward component (Bz, black line) in GSM coordinates, (e) horizontal geomagnetic field perturbations (black: ΔBx and blue: ΔBy) from the HET ground magnetometer, (f) the time derivative of horizontal magnetic field perturbations (dH/dt) from the HET ground magnetometer, (g) GIC measurements at device 10659 from the NERC GMD database. The pink and yellow bars in panels (c-d) indicate the time intervals when the satellite was located in the magnetosheath and magnetosphere, respectively. The vertical red line marks 03:55 UT, the moment when multiple sites detected an enhanced GIC. |
These significant magnetopause movements generated large-amplitude geomagnetic disturbances (GMD) in the magnetosphere and on the ground across a wide range of local times (e.g., Figures 1e and 1f). Simultaneously, large GIC were measured in New Zealand, Finland, Canada, and the United States (e.g., Figure 1g), with magnitude comparable (within factors of 2-2.5) to the largest ever recorded during ≥14 year monitoring intervals in New Zealand and Finland and represented ∼2-year maxima in the United States during a period with several Kp≥7 geomagnetic storms.
Conclusion
The limited availability of accessible GIC data and the scarcity of studies integrating spacecraft observations have hindered efforts to identify the dominant factors driving GIC variations across different places and their underlying generation processes. Our study highlights that large density pulses, which could be common, can play a critical role in driving large amplitude, global GMD and some of the largest GIC at mid-latitude locations. Furthermore, we emphasize the importance of high sampling rates (≤10s) in measurements to accurately capture these GMD and the resulting GIC (e.g., Figure 1).
References
Liu, T. Z., Shi, X., Hartinger, M. D., Angelopoulos, V., Rodger, C. J., Viljanen, A., et al. (2024). Global observations of geomagnetically induced currents caused by an extremely intense density pulse during a coronal mass ejection. Space Weather, 22, e2024SW003993. https://doi.org/10.1029/2024SW003993
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Emmanuel Masongsong / emasongsong @ igpp.ucla.edu