11:15 〜 11:30
[PCG18-09] モンテカルロモデル開発に基づく火星ディフューズオーロラ発光高度分布への磁場構造の影響の研究
キーワード：火星、オーロラ、SEP、モンテカルロ、誘導磁気圏
The Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft first observed the diffuse aurora at Mars (Schneider et al. 2015). The aurora is thought to be caused by solar energetic particles penetrating into the Martian atmosphere along the interplanetary magnetic field lines draped around the planet. The aurora was observed over a wide area in the northern hemisphere where the crustal magnetic fields are absent or weak. The energy of these solar energetic particles, measured by SEP instrument onboard MAVEN, did not show rapid variation and changed slowly over several days. On the other hand, observations by the Imaging Ultraviolet Spectrograph (IUVS) onboard MAVEN show rapid changes in the peak altitude of the diffuse aurora emission intensity. The cause of the rapid changes of the vertical auroral emission profile is far from understood. One of the possibilities is that the change in the magnetic field orientation around Mars affects the auroral altitude profile. The purpose of this study is to investigate effects of the magnetic field orientation on the vertical emission profile of Martian diffuse aurora based on a Monte Carlo simulation.
We have developed a one-dimensional (1-D) model that calculates the vertical emission profile of CO2+ UVD and the CO Cameron bands, which are typical emission lines of the diffuse aurora. The methods used are similar to that of the Monte Carlo model of Bhardwaj et al. (2009), which describes the interaction between CO2 neutral atmosphere and electrons up to 1000 eV. Our model includes elastic scattering, excitation, and ionization between electrons and CO2, and extended the upper energy up to hundreds of keV to include high-energy electrons that cause the diffuse aurora. In addition, the effect of the draped magnetic field structure was introduced by changing the incident angle of electrons through coordinate transformation. The results of our model showed that decreasing elevation angle of the magnetic field from the horizontal direction increased the peak altitude of the emission intensity. The result might indicate that the magnetic field orientation in the vicinity of the planet is one of the important factors to change the vertical emission profile of the diffuse aurora.
We have developed a one-dimensional (1-D) model that calculates the vertical emission profile of CO2+ UVD and the CO Cameron bands, which are typical emission lines of the diffuse aurora. The methods used are similar to that of the Monte Carlo model of Bhardwaj et al. (2009), which describes the interaction between CO2 neutral atmosphere and electrons up to 1000 eV. Our model includes elastic scattering, excitation, and ionization between electrons and CO2, and extended the upper energy up to hundreds of keV to include high-energy electrons that cause the diffuse aurora. In addition, the effect of the draped magnetic field structure was introduced by changing the incident angle of electrons through coordinate transformation. The results of our model showed that decreasing elevation angle of the magnetic field from the horizontal direction increased the peak altitude of the emission intensity. The result might indicate that the magnetic field orientation in the vicinity of the planet is one of the important factors to change the vertical emission profile of the diffuse aurora.