Proton Kinetic Effects and Turbulent Energy Cascade Rate in the Solar Wind

TL;DR

This study links proton kinetic instabilities and turbulence energy cascade rates in the solar wind, revealing that kinetic effects significantly influence turbulence and plasma heating at 1 AU.

Contribution

It provides the first observational evidence connecting proton temperature anisotropy-driven instabilities with turbulence cascade rates in the solar wind.

Findings

Enhanced cascade rates occur near instability boundaries.

Strong correlation between cascade rate and proton temperature anisotropy.

Protons are significantly hotter and more anisotropic in these regions.

Abstract

The first observed connection between kinetic instabilities driven by proton temperature anisotropy and estimated energy cascade rates in the turbulent solar wind is reported using measurements from the Wind spacecraft at 1 AU. We find enhanced cascade rates are concentrated along the boundaries of the ($\beta_{\parallel}$, $T_{\perp}/T_{\parallel}$)-plane, which includes regions theoretically unstable to the mirror and firehose instabilities. A strong correlation is observed between the estimated cascade rate and kinetic effects such as temperature anisotropy and plasma heating, resulting in protons 5-6 times hotter and 70-90% more anisotropic than under typical isotropic plasma conditions. These results offer new insights into kinetic processes in a turbulent regime.