Large-scale Control of Kinetic Dissipation in the Solar Wind

TL;DR

This study links large-scale turbulence in the solar wind to particle heating and energy partitioning at kinetic scales, revealing how turbulence amplitude and plasma beta influence ion and electron temperatures and anisotropies.

Contribution

It introduces turbulence amplitude as a proxy for ion heating onset and explores its relation with plasma parameters, advancing understanding of kinetic dissipation in solar wind turbulence.

Findings

Turbulence amplitude correlates with ion heating and energy partitioning.

The ratio of linear to nonlinear timescales relates to proton temperature.

Higher turbulence amplitude increases proton-to-electron temperature ratio.

Abstract

In this Letter we study the connection between the large-scale dynamics of the turbulence cascade and particle heating on kinetic scales. We find that the inertial range turbulence amplitude ($\delta B_i$; measured in the range of 0.01-0.1 Hz) is a simple and effective proxy to identify the onset of significant ion heating and when it is combined with $\beta_{||p}$, it characterizes the energy partitioning between protons and electrons ($T_p/T_e$), proton temperature anisotropy ($T_{\perp}/T_{||}$) and scalar proton temperature ($T_p$) in a way that is consistent with previous predictions. For a fixed $\delta B_i$, the ratio of linear to nonlinear timescales is strongly correlated with the scalar proton temperature in agreement with Matthaeus et al., though for solar wind intervals with $\beta_{||p}>1$ some discrepancies are found. For a fixed $\beta_{||p}$, an increase of the turbulence amplitude leads to higher $T_p/T_e$ ratios, which is consistent with the models of Chandran et al. and Wu et al. We discuss the implications of these findings for our understanding of plasma turbulence.