Low and High Energy Electron Velocity Distributions During Wave-Particle Interaction Events

Abstract:

Several wave-particle interaction events have been detected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument on the Van Allen Probes. Most of these occur during the recovery of electron injections by substorm activity. One example reported by Fennell et al [2014] occurred on January 13, 2013. The high resolution mode on MagEIS, with up to 1000 samples per spacecraft spin, provided very detailed pitch angle data for a few energy channels. This data showed quasiperiodic bursts of 30-40 keV electrons at oblique pitch angles that correlate with simultaneously detected emissions of whistler-mode, upper-band chorus. The electron bursts were superimposed on a pre-existing trapped electron distributions at that energy that were of the form sinⁿ α, where α is the pitch angle and the exponent n is approximately 0.8. The data from the Helium, Oxygen, Proton and Electron (HOPE) instrument was investigated to determine if the electron distributions at lower energy were anisotropic. An electron population with high perpendicular anisotropy could provide free energy for the generation of the observed waves. In this case, only small amounts of anisotropy were observed by HOPE. This could indicate that the wave-particle interaction could be some distance away from the Van Allen Probes. But this conclusion appears inconsistent with the electron and the waves arriving simultaneously at the spacecraft for several bursts, despite traveling at different speeds. The result will be discussed and compared with theories and models of such interactions.