Capturing Secondary Kinetic Instabilities in Three-Dimensional Dayside Reconnection Using an Improved Gradient-Based Closure

TL;DR

This paper introduces an improved gradient-based heat flux closure in a fluid model to better capture secondary kinetic instabilities and turbulence in three-dimensional magnetic reconnection, aligning simulations more closely with kinetic results.

Contribution

The study develops and applies an enhanced heat flux closure within the ten-moment fluid model to accurately simulate secondary instabilities in magnetic reconnection.

Findings

Improved closure captures secondary kinetic instabilities effectively.

Simulations show increased turbulence and magnetic island formation.

Results align more closely with kinetic simulation observations.

Abstract

Magnetic reconnection is a highly dynamic process that excites a wide variety of kinetic waves and instabilities. Transverse current sheet instabilities such as the lower-hybrid drift and secondary drift-kink instabilities in particular have been shown by kinetic simulations to modify the reconnection and introduce significant turbulence and mixing to the reconnection layer. Past studies using the ten-moment fluid model to capture important kinetic physics such as the electron inertia and full representation of the pressure tensor proved advantageous to a two-fluid representation of reconnection, but the model struggled when using a local relaxation closure for the heat flux to replicate the current sheet instabilities and subsequent mixing seen in kinetic simulations. This work uses the \texttt{Gkeyll} software framework to perform simulations of asymmetric reconnection based on the 16 October 2015 MMS crossing of a diffusion region, the Burch event. An improved gradient-based heat flux closure is implemented, showing significant improvement in secondary kinetic instabilities that grow in the current sheet. These instabilities generate turbulence which leads to growth of secondary magnetic islands and flux ropes.