Electron energy partition across interplanetary shocks: II. Statistics

TL;DR

This paper provides a comprehensive statistical analysis of electron velocity distribution functions near interplanetary shocks at 1 AU, establishing baseline parameters for different electron populations and aiding future space missions.

Contribution

It offers the first extensive statistical characterization of electron velocity moments near interplanetary shocks, including detailed parameterizations of core, halo, and beam/strahl populations.

Findings

Median electron densities: 11.3, 0.36, 0.17 cm^{-3} for core, halo, beam/strahl.

Median electron temperatures: 14.6 eV (core), 48.4 eV (halo), 40.2 eV (beam/strahl).

Median beta: 0.93 (core), 0.11 (halo), 0.05 (beam/strahl).

Abstract

A statistical analysis of 15,210 electron velocity distribution function (VDF) fits, observed within $\pm$2 hours of 52 interplanetary (IP) shocks by the $Wind$ spacecraft near 1 AU, is presented. This is the second in a three-part series on electron VDFs near IP shocks. The electron velocity moment statistics for the dense, low energy core, tenuous, hot halo, and field-aligned beam/strahl are a statistically significant list of values illustrated with both histograms and tabular lists for reference and baselines in future work. The beam/strahl fit results in the upstream are currently the closest thing to a proper parameterization of the beam/strahl electron velocity moments in the ambient solar wind. This work will also serve as a 1 AU baseline and reference for missions like $Parker \ Solar \ Probe$ and $Solar \ Orbiter$. The median density, temperature, beta, and temperature anisotropy values for the core(halo)[beam/strahl] components, with subscripts $ec$($eh$)[$eb$], of all fit results respectively are $n{\scriptstyle_{ec(h)[b]}}$ $\sim$ 11.3(0.36)[0.17] $cm^{-3}$, $T{\scriptstyle_{ec(h)[b], tot}}$ $\sim$ 14.6(48.4)[40.2] $eV$, $\beta{\scriptstyle_{ec(h)[b], tot}}$ $\sim$ 0.93(0.11)[0.05], and $\mathcal{A}{\scriptstyle_{ec(h)[b]}}$ $\sim$ 0.98(1.03)[0.93]. The nuanced details of the fitting method and data product description were published in Paper I and the detailed analysis of the results will be shown in Paper III.