Correlation between precipitation and acceleration of relativistic electrons by whistler mode chorus waves: GEMSIS-RBW simulations

Abstract:

Whistler mode chorus waves in the Earth’s magnetosphere are considered to have important roles to increase relativistic electron flux in the outer radiation belt. Kurita et al. (2016) found that whistler chorus waves responsible for flux enhancement of relativistic electrons can be a cause of precipitation of relativistic electrons. They concluded that the microbursts are a good proxy to indicate that whistler chorus activity actually causes significant variations of relativistic electrons. In order to understand physical mechanism of the causal relationship between relativistic electron flux enhancements and relativistic electron precipitation, we study flux enhancement and atmospheric precipitation of relativistic electrons associated with whistler chorus elements propagating along a magnetic field line, by using GEMSIS-RBW simulation code (RBW). The RBW is a test-particle code solving bounce motion of electrons along a field line, parallel propagating whistler mode chorus waves, and scattering of the electrons by the whistler waves. The RBW simulation can calculate scattering processes, not only scattering following quasilinear theory but also nonlinear scattering that are phase bunching and phase trapping in coherent whistler mode chorus [Saito et al. JGR 2016]. The nonlinear phase trapping leads to electron acceleration from a few hundred keV to a few MeV within a time scale of a second. Our simulations showed that both the relativistic electron flux and relativistic electron precipitation into the atmosphere are more enhanced as the whistler chorus waves propagate more away from the equator. We will discuss dependency of latitude of the whistler chorus on the flux enhancement and precipitation of relativistic electrons.

Reference

[1] Kurita, S., Y. Miyoshi, J. B. Blake, G. D. Reeves, and C. A. Kletzing (2016), Relativistic electron microbursts and variations in trapped MeV electron fluxes during the 8–9 October 2012 storm: SAMPEX and Van Allen Probes observations, Geophys. Res. Lett., 43, 3017–3025, doi:10.1002/2016GL068260.

[2] Saito, S., Y. Miyoshi, and K. Seki (2016), Rapid increase in relativistic electron flux controlled by nonlinear phase trapping of whistler chorus elements, J. Geophys. Res. Space Physics, 121, 6573–6589, doi:10.1002/2016JA022696.