On the Association Between Electron Flux Oscillations and Local Phase Space Density Gradients

Abstract

AbstractElectron flux oscillations are often observed in electron energy channels in the range of 10 keV to 100 keV. They are observed in the form of flux fluctuations with periods corresponding to the drift periods of electrons around the Earth and can be produced in the magnetosphere as a result of drift resonant interactions in association with broadband ultra‐low frequency (ULF) waves. They are observed in particular during quiet times and are indicators of ongoing drift‐resonant processes and resulting radial transport caused by ULF waves. In this study we investigate the association of the appearance of such flux oscillations with the local phase space density. In particular, it is shown that flux oscillations appear when nonzero phase space density gradients are present and furthermore that the observed amplitude of flux oscillations is dependent on radial phase space density gradients, with steeper gradients enabling the observation of flux oscillations with higher‐amplitude. Via statistical observations from the Van Allen probes twin‐spacecraft mission while at apogee at L* ∼5 to ∼5.6 it is found that, during quiet times, electron flux oscillations are more likely to diminish for electron energy of ∼400 keV, and associated phase space density is more likely to be zero for the corresponding first adiabatic invariant values of ∼300 MeV/G. It is also concluded that flux oscillations could be used as indicators of phase space density gradients.