Effects of electron temperature anisotropy on proton mirror instability evolution

TL;DR

This study uses particle-in-cell simulations to investigate how electron temperature anisotropy affects proton mirror instability, finding that electron anisotropy excites the electron whistler instability which suppresses its impact on proton mirror growth.

Contribution

It demonstrates through simulations that electron temperature anisotropy does not enhance proton mirror instability as previously thought, due to the rapid growth of electron whistler instability.

Findings

Electron whistler instability grows faster than proton mirror instability.

Electron anisotropy is quickly consumed by the whistler instability.

Electron anisotropy has negligible impact on proton mirror evolution.

Abstract

Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron free energy, so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.