Formation of Asymmetric Electron Acoustic Double Layers in the Earth's Inner Magnetosphere

Abstract

The Van Allen Probes have observed both symmetric and asymmetric bipolar electric field structures in the Earth's inner magnetosphere. In general, the symmetric bipolar structures are identified as electron-phase space holes, whereas the asymmetric structures are interpreted as electron acoustic double layers (EADLs). The generation mechanism of these EADLs is not entirely understood yet.We have modeled the EADLs observed on 13 November 2012 by Van Allen Probe-B.We performed a fluid simulation of the EADLs and tracked their formation and evolution in the simulation.We found that the localized depletion and enhancement in the electron populations act as a perturbation to excite the symmetric bipolar electron acoustic solitary waves, which later evolve into the EADLs. The Ponderomotive force is found to be the main driver behind transformation of the symmetric electron acoustic solitary waves to EADLs via formation of the electron acoustic shocks.