Large-scale Control of Kinetic Dissipation in the Solar Wind

Daniel Vech,Kristopher G Klein,Justin C Kasper

doi:10.3847/2041-8213/aad329

Daniel Vech, Kristopher G Klein + Show 1 more

Open Access

https://doi.org/10.3847/2041-8213/aad329

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Abstract

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 ( 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 , it characterizes the energy partitioning between protons and electrons (T p /T e ); proton temperature anisotropy ( ); and scalar proton temperature (T p ) in a way that is consistent with previous predictions. For a fixed δB 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 , some discrepancies are found. For a fixed , 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.

Highlights

The solar wind is ubiquitously observed to be in a turbulent state with a power spectrum of fluctuations spanning from magnetohyrodynamic (MHD) to smaller kinetic scales (e.g. Coleman Jr 1968; Siscoe et al 1968)
Goldreich & Sridhar (1995) proposed the critical balance theory predicting that the linear timescale corresponding to the propagating Alfvenic fluctuations and their nonlinear decay are comparable at each scale: τA(k⊥) ∼ τCB(k⊥) where k⊥ is the perpendicular wavenumber
We find that the (β||p, δBi) space organizes the solar wind plasma measurements in a way that is consistent with current theories about solar wind heating in particular with Chandran et al (2010), Wu et al (2013), Matthaeus et al (2016), and characterizes the protonelectron temperature ratio (Tp/Te), proton temperature anisotropy (T⊥/T||) and scalar proton temperature (Tp)

Summary

Introduction

The solar wind is ubiquitously observed to be in a turbulent state with a power spectrum of fluctuations spanning from magnetohyrodynamic (MHD) to smaller kinetic scales (e.g. Coleman Jr 1968; Siscoe et al 1968). The partitioning of the dissipated energy between protons and electrons is thought to be affected by several plasma parameters including the nonlinear timescales (Matthaeus et al 2016), gyroscale turbulence amplitude (Chandran et al 2010) and the ratio of parallel thermal pressure to magnetic pressure (Cerri et al 2017); (β||p =2μ0 np kB T||p /B02 ). A crucial factor characterizing the energy cascade rate and the relative heating of protons and electrons is the nonlinear timescale at which the energy is transferred to smaller scales (see review by Horbury et al 2012). Goldreich & Sridhar (1995) proposed the critical balance theory predicting that the linear timescale corresponding to the propagating Alfvenic fluctuations and their nonlinear decay are comparable at each scale: τA(k⊥) ∼ τCB(k⊥) where k⊥ is the perpendicular (with respect to the magnetic field) wavenumber. The Alfven time and the nonlinear “critical balance” time are estimated for a given spatial scale perpendicular to the background magnetic field (λ ∼ 2π/k⊥) as l

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