2012 THEMIS SCIENCE NUGGETS
Statistical modeling of plasmaspheric hiss amplitude using solar wind measurements and geomagnetic indices
by Daniel Golden, Stanford University
Introduction
An example of the hiss model output is shown in Figure 1. The interval from 3-5 September 2008 includes a moderate geomagnetic storm. Prior to storm onset (max SYM-H) at 21:00 UTC on 3 September, the modeled hiss amplitude is low across all L and MLT. As the storm progresses, modeled hiss amplitude initially increases significantly, rotates Eastward, and then, although reduced in amplitude from its peak, remains elevated well into the storm recovery phase. Model output, such as the example shown here, can both feed radiation belt models directly and give qualitative insight into the drivers of plasmaspheric hiss dynamics during storms.
Results
An example of the hiss model output is shown in Figure 1. The interval from 3-5 September 2008 includes a moderate geomagnetic storm. Prior to storm onset (max SYM-H) at 21:00 UTC on 3 September, the modeled hiss amplitude is low across all L and MLT. As the storm progresses, modeled hiss amplitude initially increases significantly, rotates Eastward, and then, although reduced in amplitude from its peak, remains elevated well into the storm recovery phase. Model output, such as the example shown here, can both feed radiation belt models directly and give qualitative insight into the drivers of plasmaspheric hiss dynamics during storms.
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| Figure 1. (Top) Output of the hiss model for the 04 September 2008 geomagnetic storm. (Bottom) Hiss amplitude as a function of MLT and time averaged over 2 < L < 5, and the AE, SYM-H, Pdyn and dΦMP/dt indices as a function of time. |
Conclusion
This model for plasmaspheric hiss amplitude, which includes as inputs time histories of various geomagnetic indices and solar wind parameters, can be used to estimate hiss amplitudes more accurately than simpler models which are currently used. The greater precision of estimated hiss amplitudes that may be determined using this model has the potential to improve the accuracy of radiation belt models and to further our understanding of the role of plasmaspheric hiss in the maintenance of the structure of the electron radiation belts.
References
Biographical Note
Daniel Golden is a postdoctoral scholar in the Very Low Frequency (VLF) group in the Department of Electrical Engineering at Stanford University. His previous work has involved ground-based chorus and hiss observations, and this is his first major study using in-situ satellite data. In July 2012, he will be transitioning to cancer-related biomedical imaging informatics research in Stanford’s radiology department.
Please send comments/suggestions to
Emmanuel Masongsong / emasongsong @ igpp.ucla.edu