Proton temperature anisotropy and magnetic reconnection in the solar wind: effects of kinetic instabilities on current sheet stability

TL;DR

This study uses 2-D hybrid simulations to explore how proton temperature anisotropies and associated kinetic instabilities influence magnetic reconnection and current sheet stability in the solar wind.

Contribution

It reveals the complex coupling between proton anisotropies, kinetic instabilities, and magnetic reconnection, highlighting different effects based on anisotropy type.

Findings

Proton anisotropies can enhance or stabilize tearing instability.

Linear instabilities influence current sheet stability and tearing onset.

Different anisotropies lead to varied reconnection dynamics in the solar wind.

Abstract

We investigate the role of kinetic instabilities driven by a proton anisotropy on the onset of magnetic reconnection by means of 2-D hybrid simulations. The collisionless tearing of a current sheet is studied in the presence of a proton temperature anisotropy in the surrounding plasma. Our results confirm that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated to linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. We find that such a complex coupling leads to a faster tearing evolution in a regime with larger perpendicular temperature when an ion-cyclotron instability is generated by the anisotropic proton distribution functions. On the contrary, in the presence of the opposite anisotropy, fire hose fluctuations excited by the unstable background protons with larger parallel temperature are not able to efficiently destabilize the current sheets, which remain stable for a long time after fire hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.