[P-EM09] 宇宙天気・宇宙気候

[PEM09-19] Thermospheric mass density variations at altitudes between 150-250 km

★Invited Papers

*藤原 均¹、三好 勉信²、片岡 龍峰³ (1.成蹊大学サステナビリティ教育研究センター/理工学部、2.九州大学大学院理学研究院、3.国立極地研究所)

キーワード：熱圏、質量密度、低高度衛星

Thermospheric mass density is one of the most difficult parameters to predict its spatio-temporal variations. For example, annual and semi-annual variations of the thermospheric mass density are so complex that we cannot reproduce the variations with the numerical models. Furthermore, significant variations of the thermospheric mass density are occurred during/after geomagnetically disturbed periods. We should understand these variations of the thermospheric mass density for the safety and efficient operation of the artificial satellites, in particular, the Low Earth Orbit (LEO) satellites. It is well-known that sudden changes in the thermospheric mass density sometimes affect the satellite attitude through enhancements of the atmospheric drag force. Recently (February in 2022), many information media reported that SpaceX would lose up to 40 of 49 newly launched Starlink satellites as the result of a geomagnetic storm which was caused by the solar coronal mass ejection. These solar outbursts would increase the atmospheric drag by at least 50 percent higher than during previous launches. This case as a space weather event suggests the importance of understanding the thermospheric mass density at altitude of about 210 km, a preliminary "low-deployment" orbit. In this presentation, we will review the previous studies abut the thermospheric mass density at altitudes between 150-250 km. The modeling activities will be also shown. We introduce our research project to develop a method for modeling the thermospheric mass density variations using low-altitude satellite data and GCM simulations.