# An extended MHD study of the 16 October 2015 MMS diffusion region crossing

## TL;DR

This paper uses advanced multi-fluid MHD models within the Gkeyll framework to analyze the 16 October 2015 MMS magnetic reconnection event, comparing results with MMS data and PIC simulations to understand kinetic effects.

## Contribution

It introduces extended multi-fluid MHD models that incorporate kinetic effects like electron pressure tensor and Landau damping, providing a less costly alternative to PIC simulations for studying magnetic reconnection.

## Key findings

- Multi-fluid MHD models can replicate key features of the MMS reconnection event.
- Inclusion of kinetic effects improves the accuracy of fluid models.
- Comparison shows the trade-offs between model complexity and physical fidelity.

## Abstract

The Magnetospheric Multiscale (MMS) mission has given us unprecedented access to high cadence particle and field data of magnetic reconnection at Earth's magnetopause. MMS first passed very near an X-line on 16 October 2015, the Burch event, and has since observed multiple X-line crossings. Subsequent 3D particle-in-cell (PIC) modeling efforts of and comparison with the Burch event have revealed a host of novel physical insights concerning magnetic reconnection, turbulence induced particle mixing, and secondary instabilities. In this study, we employ the Gkeyll simulation framework to study the Burch event with different classes of extended, multi-fluid magnetohydrodynamics (MHD), including models that incorporate important kinetic effects, such as the electron pressure tensor, with physics-based closure relations designed to capture linear Landau damping. Such fluid modeling approaches are able to capture different levels of kinetic physics in global simulations and are generally less costly than fully kinetic PIC. We focus on the additional physics one can capture with increasing levels of fluid closure refinement via comparison with MMS data and existing PIC simulations.