16:30 〜 16:45
[PEM09-26] HF radar blackouts at Mars: A preliminary data-model comparison
キーワード：火星、レーダーブラックアウト、太陽高エネルギー粒子、電離圏
Recent observations have revealed that the precipitation of solar energetic particles (SEPs) drives a variety of phenomena in the Martian upper atmosphere. A prominent example is diffuse aurora displaying spatially extended emission from the entire nightside of Mars during SEP events. For diffuse aurora, a Monte Carlo model of SEP interaction with the Martian atmosphere developed by Nakamura et al. successfully reproduced the relative altitude profiles of auroral emission observed by MAVEN during the December 2014 and September 2017 SEP events.
Meanwhile, the SEP precipitation causes another observable signature related to the Martian ionosphere, i.e., a significant attenuation of high-frequency (HF) trans-ionospheric radar signals transmitted from and received by orbiters (called radar blackouts) owing to the enhanced ionization and electron-neutral collision below ~100 km altitude. In this study, we conduct an additional test of Nakamura et al.'s model against observations by utilizing MARSIS observations of HF radar signal absorption during the December 2014 event. During this event, MARSIS operated in the active ionospheric sounding mode for many of the periapsis segments of Mars Express. The obtained data show the surface reflection with a range of intensities along with nightside ionospheric echoes. The surface echo intensity anti-correlates with SEP fluxes measured by MAVEN, enabling a quantitative evaluation of the electron density profiles predicted by the model. Here we report the preliminary results of the data-model comparison on the ionospheric effects of SEP precipitation on HF radar measurements during the December 2014 event.
Meanwhile, the SEP precipitation causes another observable signature related to the Martian ionosphere, i.e., a significant attenuation of high-frequency (HF) trans-ionospheric radar signals transmitted from and received by orbiters (called radar blackouts) owing to the enhanced ionization and electron-neutral collision below ~100 km altitude. In this study, we conduct an additional test of Nakamura et al.'s model against observations by utilizing MARSIS observations of HF radar signal absorption during the December 2014 event. During this event, MARSIS operated in the active ionospheric sounding mode for many of the periapsis segments of Mars Express. The obtained data show the surface reflection with a range of intensities along with nightside ionospheric echoes. The surface echo intensity anti-correlates with SEP fluxes measured by MAVEN, enabling a quantitative evaluation of the electron density profiles predicted by the model. Here we report the preliminary results of the data-model comparison on the ionospheric effects of SEP precipitation on HF radar measurements during the December 2014 event.