[P-CG19] 惑星大気圏・電磁圏

[PCG19-08] Three-dimensional simulation of the Martian diffuse auroral emission in the crustal magnetic field regions

*中村 勇貴^1,2,3、Leblanc Francois²、Gérard Jean-Claude⁴、Soret Lauriane⁴、寺田 直樹¹、中川 広務¹、堺 正太朗^1,5、村瀬 清華^6,7、片岡 龍峰^6,7、Brain Dave A.⁸、関 華奈子³ (1.東北大学大学院理学研究科地球物理学専攻、2.LATMOS, Sorbonne Université、3.東京大学理学系研究科地球惑星科学専攻、4.LPAP, STAR Institute, Université de Liège、5.東北大学大学院理学研究科惑星プラズマ・大気研究センター、6.国立極地研究所、7.総合研究大学院大学、8.Laboratory for Atmospheric and Space Physics, University of Colorado Boulder)

キーワード：火星、ディフューズオーロラ、太陽高エネルギー粒子

The recent discovery of the Martian diffuse aurora, which spans the whole nightside Mars due to the precipitation of solar energetic particles (SEPs), has highlighted that SEPs globally impacted the Martian atmosphere at low altitudes [Schneider et al., 2015, 2018]. Our recent Monte Carlo model, which is one dimension in space vertically without considering magnetic fields, has shown that both the SEP electrons and protons should have been at the origin of the Martian diffuse auroral emissions during the SEP events in December 2014 and September 2017 [Nakamura et a., 2022]. The spatial structure of the Martian diffuse auroral emission would provide insight into how SEPs precipitate into the Martian atmosphere through the magnetic field environment around Mars, however, it is still poorly understood due to the small number of observations.

In this study, we extend our Monte Carlo model to three dimensions with magnetic fields to investigate the effects of the crustal magnetic fields in the southern hemisphere of Mars on the spatial distribution of the Martian diffuse auroral emission. Our results show different morphology for the electron- and proton-induced emissions in the crustal magnetic field region due to the difference in their gyro radii. The electron-induced CO₂⁺ UVD emission is patchy and bright in the cusp regions because the concentration of precipitating electrons into the cusp regions compensates for the magnetic mirror effect, while the proton-induced CO₂⁺ UVD emission is diffuse without any fine structures. We also simulated atomic oxygen 557.7 nm and 630.0 nm emission lines, which have not yet been observed as auroral emissions on Mars. The oxygen 557.7 nm emission is similar in shape and intensity to the CO₂⁺ UVD emission. The oxygen 630.0 nm emission is restricted to the cusp regions, SEP electron precipitation being its dominant source because proton-induced emission is completely quenched at low altitudes.