SM21A-2509
The statistics of relativistic electron pitch angle distribution in the Earth’s radiation belt based on the Van Allen Probes measurements

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Reiner H W Freidel1, Hong Zhao2, Yue Chen3, Michael G Henderson1, Shrikanth G Kanekal4, Daniel N. Baker5, Harlan E. Spence6 and Geoffrey D Reeves1, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)University of Colorado at Boulder, LASP and Aerospace Engineering Sciences, Boulder, CO, United States, (3)LANL, Los Alamos, NM, United States, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)University of Colorado at Boulder, Boulder, CO, United States, (6)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States
Abstract:

The relativistic electron pitch angle distribution (PAD) is an important characteristic of radiation belt electrons, which can give information on source or loss processes in a specific region. Using data from MagEIS and REPT instruments onboard the Van Allen Probes, a statistical survey of relativistic electron pitch angle distribution (PAD) is performed. By fitting relativistic electron PADs to Legendre polynomials, an empirical model of PADs as a function of L (from 1.4 to 6), MLT, electron energy (~100 keV – 5 MeV), and geomagnetic activity is developed and many intriguing features are found. In the outer radiation belt, an unexpected dawn/dusk asymmetry of ultra-relativistic electrons is found during quiet times, with the asymmetry becoming stronger at higher energies and at higher L shells. This may indicate the existence of physical processes acting on the relativistic electrons on the order of drift period, or be a signature of the partial ring current. In the inner belt and slot region, 100s of keV pitch angle distributions with minima at 90° are shown to be persistent in the inner belt and appears in the slot region during storm times. The model also shows clear energy dependence and L shell dependence of 90°-minimum pitch angle distribution. On the other hand, the head-and-shoulder pitch angle distributions are found during quiet times in the slot region, and the energy, L shell and geomagnetic activity dependence of those PADs are consistent with the wave-particle interaction caused by hiss waves.

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