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

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. In particular,
we find that the ten-moment model well captures the agyrotropic structure
of the pressure tensor in the vicinity of the X-line and the magnitude of
anisotropic electron heating observed in MMS and PIC simulations. However,
the ten-moment model has difficulty resolving the lower hybrid drift
instability, which has been observed to plays a fundamental role in
heating and mixing electrons in the current layer.