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

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Title: Study of Variation Mechanisms of the Martian Diffuse Aurora Based on Monte Carlo Simulations and MAVEN Observations.
Authors: Okiyama, Taishin1 (AUTHOR) t.okiyama@eps.s.u-tokyo.ac.jp, Seki, Kanako1 (AUTHOR), Nakamura, Yuki1 (AUTHOR), Lillis, Robert J.2 (AUTHOR), Rahmati, Ali2 (AUTHOR), Larson, Davin E.2 (AUTHOR), DiBraccio, Gina A.3 (AUTHOR), Schneider, Nicholas M.4 (AUTHOR), Jain, Sonal K.4 (AUTHOR), Sakata, Ryoya5 (AUTHOR), Curry, Shannon4 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Feb2025, Vol. 130 Issue 2, p1-17. 17p.
Subject Terms: Magnetic field effects, Magnetic flux density, Solar energetic particles, Magnetic structure, Monte Carlo method
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. Plain Language Summary: Martian diffuse auroras are ultraviolet emissions spread across the nightside of Mars caused by high‐energy electrons and protons from the Sun. The diffuse auroral emissions caused by electrons are expected to vary with nightside magnetic field structures around Mars. However, the effects of the magnetic fields on diffuse auroral emission profiles are far from understood. This study shows an estimation of the magnetic field effects based on a newly developed model and spacecraft observations. The model results under uniform magnetic field assumptions show that the effects of magnetic field directions on auroral altitude profiles are greater than those of magnetic field intensity, and the more horizontal magnetic fields result in broader auroral altitude profiles. The magnetic field structure can be one of the important factors in understanding the Martian diffuse auroras. Key Points: A Monte Carlo model including electron cyclotron motion was developed to study the effects of magnetic field structure on diffuse aurorasUnder uniform magnetic fields, effects of magnetic field dip angle on auroral altitude profiles are greater than those of field intensitySystematic broadening of auroral altitude profiles with horizontal dip angle increases auroral intensity at high altitudes (>75 km) [ABSTRACT FROM AUTHOR]
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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. Plain Language Summary: Martian diffuse auroras are ultraviolet emissions spread across the nightside of Mars caused by high‐energy electrons and protons from the Sun. The diffuse auroral emissions caused by electrons are expected to vary with nightside magnetic field structures around Mars. However, the effects of the magnetic fields on diffuse auroral emission profiles are far from understood. This study shows an estimation of the magnetic field effects based on a newly developed model and spacecraft observations. The model results under uniform magnetic field assumptions show that the effects of magnetic field directions on auroral altitude profiles are greater than those of magnetic field intensity, and the more horizontal magnetic fields result in broader auroral altitude profiles. The magnetic field structure can be one of the important factors in understanding the Martian diffuse auroras. Key Points: A Monte Carlo model including electron cyclotron motion was developed to study the effects of magnetic field structure on diffuse aurorasUnder uniform magnetic fields, effects of magnetic field dip angle on auroral altitude profiles are greater than those of field intensitySystematic broadening of auroral altitude profiles with horizontal dip angle increases auroral intensity at high altitudes (>75 km) [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2024JA033420