Simulation of Observed Magnetic Holes in the Magnetosheath

TL;DR

This paper uses particle-in-cell simulations to model magnetic holes in Earth's magnetosheath, revealing how mirror instability dynamics produce magnetic peaks and deep holes depending on plasma stability.

Contribution

It introduces an expanding box PIC simulation approach to replicate observed magnetic holes and analyze their formation related to mirror instability.

Findings

Magnetic peaks dominate in mirror unstable plasma.

Deep magnetic holes form in marginally mirror stable plasma.

Magnetic holes are highly unstable to mirror instability.

Abstract

Magnetic holes have been frequently observed in the magnetosheath of Earth and it is believed that these structures are the result of nonlinear evolution of mirror instability. Mirror mode fluctuations mostly appear as magnetic holes in regions where plasma is marginally mirror stable with respect to the linear instability. We present an expanding box particle in cell simulation to mimic the magnetosheath plasma and produce the mirror mode magnetic holes. We show that magnetic peaks are dominant when plasma is mirror unstable and mirror fluctuations evolve to deep magnetic holes when plasma is marginally mirror stable. Although, the averaged plasma parameters in the simulation are marginally close to mirror instability threshold, the plasma in the magnetic holes is highly unstable to mirror instability and mirror stable in the magnetic peaks.