Solar wind electrons

TLDR

The measured electron velocity distributions in the solar wind are generally symmetric about the heat‑flux direction and can be described by a superposition of a low‑energy nearly bi‑Maxwellian and a distinct high‑energy bi‑Maxwellian component. The authors present an alternate self‑consistent description of the high‑energy component as an unbound hot electron population above ≈60 V, discuss how its salient parameters vary with high‑speed streams, and argue for local regulation of the solar‑wind heat flux at 1 AU. Heat conduction in the solar wind is carried by convection of the hot electron component relative to the bulk flow. The study reports average characteristics and variation ranges of solar‑wind electron velocity distributions, noting that the largest‑scale parameter variations are associated with high‑speed streams and supporting local heat‑flux regulation.

Abstract

Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi-Maxwellian function which characterizes the low-energy electrons and a bi-Maxwellian function which characterizes a distinct, ubiquitous component of higher-energy electrons. An alternate self-consistent description of the higher-energy component is presented in terms of an unbound population of hot electrons with energy greater than some breakpoint energy of ≃60 V. The largest-scale parameter variations appear to come most often in association with high-speed streams. The salient electron parameter variations associated with these structures are presented and discussed. The mechanism by which interplanetary electrons conduct heat is convection of the hot component relative to the bulk speed. Arguments are presented which favor the local regulation of the solar wind heat flux at 1 AU.