An association between anisotropic plasma heating and instabilities in the solar wind

TL;DR

This paper investigates how anisotropic plasma heating in the solar wind relates to plasma instabilities, revealing temperature enhancements near instability thresholds and suggesting mechanisms for energy transfer in space plasmas.

Contribution

It provides observational evidence linking proton temperature anisotropies to plasma instabilities and proposes a new explanation for heating near the firehose instability.

Findings

$T_{ot p}$ increases near mirror instability threshold

$T_{ ormalsize p}$ increases near firehose instability threshold

Firehose instability may convert bulk energy into thermal energy

Abstract

We present an analysis of the components of solar wind proton temperature perpendicular and parallel to the local magnetic field as a function of proximity to plasma instability thresholds. We find that $T_{\perp p}$ is enhanced near the mirror instability threshold and $T_{\parallel p}$ is enhanced near the firehose instability threshold. The increase in $T_{\perp p}$ is consistent with cyclotron-resonant heating, but no similar explanation for hot plasma near the firehose limit is known. One possible explanation is that the firehose instability acts to convert bulk energy into thermal energy in the expanding solar wind, a result with significant implications for magnetized astrophysical plasma in general.