Studying the Important Relationship Between Earth's Plasma Sheet and the Outer Radiation Belt Electrons Using Newly Calibrated and Corrected Themis-Sst Data
Abstract
Most recently, the solid-state telescope (SST) data from the THEMIS mission, which consisted of 5 spacecraft in highly elliptic, equatorial orbits that have traversed the outer radiation belt and sampled the plasma sheet for more than 4 years, have been characterized, calibrated, and decontaminated. Here, we present a brief introduction on this corrected dataset and go into detail on the valuable resource it provides to address science questions concerning the important relationship between ~1 keV-10's keV electrons in the plasma sheet and 100's keV-MeV electrons in Earth's outer radiation belt. We demonstrate this by presenting preliminary results on: studying phase space density (PSD) radial gradients for fixed first and second adiabatic invariants from the radiation belt into the plasma sheet, examining pitch angle distributions near the boundary between these two regions, and studying the boundary region itself around the last closed drift shell and the role of magnetopause shadowing losses. We examine the dependence of PSD radial gradients on the first and second invariants to test previous results [e.g., Turner et al., GRL, 2008; Kim et al., JGR, 2010] that reveal mostly positive radial gradients for lower energy electrons (10's - couple hundred keV) but negative gradients for relativistic electrons beyond geosynchronous orbit. This directly relates to the current theory that lower energy electrons have a source in the plasma sheet and are introduced to the ring current and radiation belt via substorm injections and enhanced convection, and these particles then generate the waves necessary to accelerate a fraction of this seed population to relativistic energies, providing a source of the outer radiation belt. Next, we take advantage of the pitch angle resolved differential energy fluxes to examine variations in pitch angle distributions to establish the role that Shabansky drift orbits, which break electrons' second adiabatic invariant, play on outer belt electron dynamics. Finally, THEMIS spacecraft often sample the last closed drift shell and the dayside magnetopause, and we use this new dataset to investigate dynamics in this important region as well as losses to the outer boundary, which may be critical to outer radiation belt dropout events. These preliminary examples are just a small sampling of the variety of studies that can be conducted with the THEMIS-SST dataset. We conclude with a brief discussion of how this corrected dataset should prove invaluable for sampling the source population in the plasma sheet and the outer radiation belt beyond geosynchronous orbit during the upcoming NASA Radiation Belt Storm Probes mission.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMSM24A..03C
- Keywords:
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- 2720 MAGNETOSPHERIC PHYSICS / Energetic particles: trapped;
- 2764 MAGNETOSPHERIC PHYSICS / Plasma sheet;
- 2774 MAGNETOSPHERIC PHYSICS / Radiation belts;
- 2794 MAGNETOSPHERIC PHYSICS / Instruments and techniques