SM44B-02
Investigating geomagnetic activity dependent sources of 100s of keV electrons in Earth’s inner radiation belt using Van Allen Probes observations
Thursday, 17 December 2015: 16:15
2009 (Moscone West)
Drew L Turner1, Thomas Paul O'Brien III2, Joseph F. Fennell1, Seth G Claudepierre2, J Bernard Blake1, Daniel N. Baker3, Michael G Henderson4 and Geoffrey D Reeves4, (1)Aerospace Corporation El Segundo, El Segundo, CA, United States, (2)Aerospace Corporation Santa Monica, Santa Monica, CA, United States, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Los Alamos National Laboratory, Los Alamos, NM, United States
Abstract:
By providing an unprecedented level of reliability in particle flux observations at low L-shells, NASA’s Van Allen Probes mission has yielded a series of discoveries and unanswered questions concerning the inner electron radiation belt. Two such discoveries are: 1) a sharp cutoff in the energy distribution of electrons at ~900 keV, such that fluxes of electrons with energies greater than ~900 keV are below the detectability threshold of the Van Allen Probes’ MagEIS instruments and consistent with upper flux limits of multi-MeV electrons calculated using the Van Allen Probes’ REPT instruments, and 2) that impulsive injections of up to several hundred keV electrons may act as an activity-dependent source of electrons in the slot and inner radiation belt. In this presentation, we discuss results from phase space density (PSD) analysis of inner zone electrons. Such analysis, which examines PSD as a function of the three adiabatic invariants, effectively removes adiabatic variations in the particle observations allowing one to better identify source and loss processes ongoing in the system. We demonstrate that impulsive injections do indeed act as a source of inner radiation belt electrons and, when combined with losses in the slot region, can result in peaked radial distributions of electron PSD in the inner zone. We briefly discuss the nature of these low-L injections, which penetrate inside the plasmasphere and display strong energy and species dependencies. By examining such injections throughout the Van Allen Probes era, we also i) determine the occurrence rate of injections as a function of electron energy (and first adiabatic invariant), geomagnetic activity level, and L-shell; ii) estimate the contribution of such injections to the inner belt population; and iii) investigate how such injections disrupt coherent banded flux structures in the inner zone known as “zebra stripes”.
