Study of Variation Mechanisms of the Martian Diffuse Aurora Based on Monte Carlo Simulations and MAVEN Observations

Abstract

Martian diffuse auroras are ultraviolet emissions spread across the nightside of Mars caused by solar energetic particles (SEP), both electrons and protons. The nightside structures of induced and crustal magnetic fields are expected to affect the diffuse auroral emission profiles caused by electrons, which is far from understood. Here we estimate magnetic field effects on emission based on a newly developed Monte Carlo model simulating collisions and electron cyclotron motions. Parameter surveys of the magnetic field intensity and dip angle (angle of magnetic field line from horizontal direction) under uniform magnetic field structure show that the effects of magnetic field dip angle on auroral altitude profiles are greater than those of magnetic field intensity. We then applied our model to the September 2017 diffuse aurora event using MAVEN SEP electron flux observations and neutral atmospheric profile from the Mars Climate Database as inputs. Comparison between horizontal and vertical magnetic field dip angle cases indicates that the horizontal dip angle case results in broader limb-integrated auroral altitude profiles than the vertical case and enhances the auroral intensity at high altitudes (>75 km). The magnetic field structure can be one of the important factors in understanding the Martian diffuse auroras.