[P-CG19] 惑星大気圏・電磁圏

[PCG19-06] レーダーサウンディング観測とその場観測による火星電離圏不規則構造の駆動源の研究

*坂東 日菜¹、原田 裕己¹、寺田 直樹²、中川 広務² (1.京都大学、2.東北大学)

キーワード：火星、電離圏不規則構造

Since Mars has no intrinsic magnetic field, the solar wind directly interacts with the Martian ionosphere, leading to ionospheric disturbances driven by the solar wind. Meanwhile, MAVEN observations in the dayside ionosphere indicated that variations in ion density profiles typically follow those in the neutral density profile, suggesting an ion-neutral coupling in the upper atmosphere (Mayyasi et al., 2019). Gurnett et al. (2008) reported that ''diffuse echoes'' sometimes appear on an ionogram obtained by the topside ionospheric sounding of Mars Express (MEX). These echoes are presumed to be caused by irregularities in the Martian ionosphere. However, detailed properties of ionospheric irregularities that cause diffuse echoes are still unknown. In this study, to reveal properties and drivers of these irregularities we surveyed conjunction events in which MEX and MAVEN observed the ionosphere of Mars at nearly the same time and the same location. For each conjunction event we found, we compared the echoes obtained by MEX and in-situ observation data by MAVEN. We then investigate the relationship between the diffuseness of the echoes and the in-situ disturbances such as the electron density in the ionosphere and classified events according to estimated driving sources. Based on the analysis, case studies of strong diffuse echo events suggest that there could be multiple drivers causing ionospheric irregularities, such as impacts of the solar wind and ion-neutral coupling. Additionally, diffuse echoes tend to coincide with severe electron density disturbances. This reinforces the hypothesis that the disturbance of the electron density in the ionosphere creates the diffuse echo on the ionogram. In this presentation, we discuss the relative importance and properties of multiple drivers.