Direct measurements of chorus wave effects on electrons in the 5-40 KeV range from the Van Allen Probes Mission (Invited)

Abstract:

The Van Allen Probe mission with its dual spacecraft and exquisite particle and wave instrumentation was designed to explore the effects of magnetospheric waves on the in-situ particle populations. Here we use data from the mission's low energy instrument (HOPE - Helium, Oxygen, Proton and Electron plasma instrument) to investigate the detailed changes in the electron distribution function of electrons that are drifting through a region of chorus waves. To do this we exploit the spacecraft mission constellation where two spacecraft are on the same orbit with changing separation in time. There are many times when spacecraft cross similar radial regions but separated by up to several hours in local time. We focus on the region of most active chorus wave activity, just outside the plasmapause, and focus on the energy range of particles most strongly affected by chorus waves (10's of keV, the top energy range of HOPE). We select time periods where one of the Van Allen Probes is at early local times where no wave activity is observed, while the other Probe is at later local times and in regions where wave activity is observed, and seek out changes in the pitch angle distribution of the electrons that drift from the first probe to the second. We will additionally use a recently developed wave-proxy from the low Earth orbiting NPOES satellites to fill in the local time extend of the chorus wave region, and hope to relate the changes in electron pitch angle shape to the size of the chorus regions they have drifted through. Preliminary results form a few case studies will be presented here.