Electron energy partition across interplanetary shocks: I. Methodology and Data Product

Abstract

Analysis of 15314 electron velocity distribution functions (VDFs) within $\pm$2 hours of 52 interplanetary (IP) shocks observed by the \emph{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 velocity distribution function, while both the halo and beam/strahl components were best fit to bi-kappa velocity distribution function. This is the first statistical study to show that the core electron distribution is better fit to a self-similar velocity distribution function 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 range of values defined by the lower and upper quartiles for the kappa exponents are $\kappa {}_{ec}$ $\sim$ 5.40--10.2 for the core, $\kappa {}_{eh}$ $\sim$ 3.58--5.34 for the halo, and $\kappa {}_{eb}$ $\sim$ 3.40--5.16 for the beam/strahl. The lower-to-upper quartile range of symmetric bi-self-similar core exponents are $s{}_{ec}$ $\sim$ 2.00--2.04, and asymmetric bi-self-similar core exponents are $p{}_{ec}$ $\sim$ 2.20--4.00 for the parallel exponent, and $q{}_{ec}$ $\sim$ 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.

35 pages, 10 figures, 3 tables, under review in Astrophys. J. Suppl [updated in response to 2nd round of referee comments]

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