Electron Energy Partition across Interplanetary Shocks. I. Methodology and Data Product.

Lynn B Wilson Iii,Shan Wang,Katherine A Goodrich,Chadi S Salem,Michael L Stevens,Marc P Pulupa,Steven J Schwartz,Adnane Osmane,Drew L Turner,Li-Jen Chen,Stuart D Bale,Damiano Caprioli,Justin C Kasper

doi:10.3847/1538-4365/ab22bd

Abstract

Analyses of 15,314 electron velocity distribution functions (VDFs) within ±2 hr of 52 interplanetary (IP) shocks observed by the Wind spacecraft near 1 au are introduced. The electron VDFs are fit to the sum of three model functions for the cold dense core, hot tenuous halo, and field-aligned beam/strahl component. The best results were found by modeling the core as either a bi-kappa or a symmetric (or asymmetric) bi-self-similar VDF, while both the halo and beam/strahl components were best fit to bi-kappa VDF. This is the first statistical study to show that the core electron distribution is better fit to a self-similar VDF than a bi-Maxwellian under all conditions. The self-similar distribution deviation from a Maxwellian is a measure of inelasticity in particle scattering from waves and/or turbulence. The ranges of values defined by the lower and upper quartiles for the kappa exponents are κec ~ 5.40–10.2 for the core, κeh ~ 3.58–5.34 for the halo, and κeb ~ 3.40–5.16 for the beam/strahl. The lower-to-upper quartile range of symmetric bi-self-similar core exponents is sec ~ 2.00–2.04, and those of asymmetric bi-self-similar core exponents are pec ~ 2.20–4.00 for the parallel exponent and qec ~ 2.00–2.46 for the perpendicular exponent. The nuanced details of the fit procedure and description of resulting data product are also presented. The statistics and detailed analysis of the results are presented in Paper II and Paper III of this three-part study.

Highlights

AND MOTIVATIONThe solar wind is an ionized gas experiencing collective effects where Coulomb collisions occur, but the rates are often so low that, for instance, two constituent particle species, s and s, are not in thermodynamic or thermal equilibrium, i.e., (T s /T s) tot = 1 for s = s, Vperp [1000 km/s] Core Halo a b Beam/Strahl cVpara [1000 km/s]Phase Space Density [SWF, # s3 km-3 cm-3] fParallel Cut Perpendicular CutVelocity [1000 km/s]is shown in the ion bulk flow rest frame
Analysis of 15,314 electron velocity distribution functions (VDFs) within ±2 hours of 52 interplanetary (IP) shocks observed by the Wind spacecraft near 1 AU are introduced
Livadiotis 2015, 2017; Nicolaou et al 2018; Schunk 1975, 1977; Schwartz & Marsch 1983; Schwartz et al 1988; Shizgal 2018). In this first part of a multi-part study we describe the methodology and numerical analysis techniques used to model the solar wind eVDFs below ∼1.2 keV observed by the Wind spacecraft near 1 AU around 52 interplanetary (IP) shocks

Summary

Introduction

The solar wind is an ionized gas experiencing collective effects where Coulomb collisions occur, but the rates are often so low that, for instance, two constituent particle species, s and s, are not in thermodynamic or thermal equilibrium, i.e., (T s /T s) tot = 1 for s = s, Vperp [1000 km/s] Core Halo a b Beam/Strahl c. Phase Space Density [SWF, # s3 km-3 cm-3] f. Is shown in the ion bulk flow rest frame

Methods

Discussion

Conclusion