Statistics of Kinetic Dissipation in Earth's Magnetosheath -- MMS Observations

TL;DR

This study analyzes pressure-dilatation and pressure strain interactions in Earth's magnetosheath using MMS data, revealing energy conversion patterns similar to kinetic simulations and highlighting spatially concentrated dissipation near current sheets.

Contribution

It provides the first statistical analysis of Pi-D in Earth's magnetosheath based on MMS observations, linking empirical data with kinetic simulation results.

Findings

Pi-D statistics resemble kinetic simulation results.

Energy conversion occurs near intense current sheets.

Dissipation is spatially concentrated, not within current sheets.

Abstract

A familiar problem in space and astrophysical plasmas is to understand how dissipation and heating occurs. These effects are often attributed to the cascade of broadband turbulence which transports energy from large scale reservoirs to small scale kinetic degrees of freedom. When collisions are infrequent, local thermodynamic equilibrium is not established. In this case the final stage of energy conversion becomes more complex than in the fluid case, and both pressure-dilatation and pressure strain interactions (Pi-D $\equiv -\Pi_{ij} D_{ij}$) become relevant and potentially important. Pi-D in plasma turbulence has been studied so far primarily using simulations. The present study provides a statistical analysis of Pi-D in the Earth's magnetosheath using the unique measurement capabilities of the Magnetospheric Multiscale (MMS) mission. We find that the statistics of Pi-D in this naturally occurring plasma environment exhibit strong resemblance to previously established fully kinetic simulations results. The conversion of energy is concentrated in space and occurs near intense current sheets, but not within them. This supports recent suggestions that the chain of energy transfer channels involves regional, rather than pointwise, correlations.