SM43B-4296:
Correlations between chorus properties and electron velocity distributions: Van Allen Probes

Thursday, 18 December 2014
Xiangrong Fu1, Misa Cowee1, S Peter Gary1,2, Kaijun Liu3, Kyungguk Min3 and Dan Winske1, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)Space Science Institute Boulder, Boulder, CO, United States, (3)Auburn University, Auburn, AL, United States
Abstract:
Magnetospheric chorus consists of whistler waves driven unstable by anisotropic
electron velocity distributions. A gap in the power spectrum of chorus at a fre-
quency close to half the electron cyclotron frequency (Ωe/2) are often observed
so that chorus can be categorized into four types accordingly: banded chorus
(with two bands in the spectrum separated by Ωe/2), lower band only (with
only one band below Ωe/2), upper band only (with only one band above Ωe/2)
and broadband (with only one band including Ωe/2). Here we present a study
to correlate chorus properties with electron velocity distributions based on the
hypothesis that each band of chorus is excited by an anisotropic electron com-
ponent. On Jan 14 2013, Van Allen Probes satellite A measured strong chorus
activity, and all four types were observed. We analyze HOPE and EMFISIS data
and show that there is a good correlation between the observed wave frequency
and propagation direction and the predictions of kinetic linear dispersion theory
using electron component densities and temperatures obtained by fitting HOPE
data to a multi-component bi-Maxwellian distribution function. However, the
temperature anisotropies observed by HOPE are usually close to the instabil-
ity threshold and therefore it is not possible at this point to predict whether a
certain band can be excited based on measured electron velocity distributions.
LA-UR-14-26177.