[P-CG24] [EJ] 惑星大気圏･電磁圏

[PCG24-08] MAVEN/NGIMS observations and full-particle DSMC modeling of gravity waves in the Martian upper thermosphere

*寺田 直樹¹、寺田 香織¹、中川 広務¹、前田 紗和¹、Leblanc Francois²、Medvedev Alexander³、Yigit Erdal⁴、黒田 剛史^5,1、原 拓也⁶、England Scott⁶、藤原 均⁷、関 華奈子⁸、Mahaffy Paul⁹、Elrod Meredith⁹、Benna Mehdi⁹、Grebowsky Joseph⁹、Jakosky Bruce¹⁰ (1.東北大学大学院理学研究科、2.Laboratoire Atmospheres, Milieux, Observations Spatiales - CNRS/IPSL、3.Max Planck Institute for Solar System Research、4.Department of Physics and Astronomy, George Mason University、5.情報通信研究機構　統合ビッグデータ研究センター　ビッグデータ利活用研究室、6.Space Sciences Laboratory, University of California, Berkeley、7.成蹊大学理工学部、8.東京大学大学院理学系研究科、9.NASA Goddard Space Flight Center、10.Laboratory for Atmospheric and Space Physics, University of Colorado Boulder)

キーワード：Gravity waves、Upper thermosphere、Mars

Global distribution and parameter dependences of gravity wave activity in the Martian upper thermosphere have been analyzed using density profiles obtained by the Neutral Gas Ion Mass Spectrometer (NGIMS) onboard the MAVEN spacecraft. The average amplitude of gravity waves around the Martian exobase is ~10% on the dayside and ~20% on the nightside, which is about two and ten times larger than those on Venus and in the low latitude region of Earth, respectively. The amplitudes are inversely proportional to the background atmospheric temperature, suggesting saturation due to convective instability in the Martian upper thermosphere. After removing the dependence on the background temperature, dependences of the average amplitude on the geographic latitude and longitude and solar wind parameters are found to be not larger than a few percent. These results suggest that the amplitudes of gravity waves are mainly determined by convective breaking/saturation in the upper thermosphere on Mars, unlike those on Venus and Earth. We have also performed numerical simulations of propagation, saturation, and dissipation processes of gravity waves in the Martian upper thermosphere using a full-particle Direct Simulation Monte-Carlo (DSMC) model. The modeling results are compared to the NGIMS observations with a particular emphasis on the vertical profiles of the wave amplitudes and their day-night variations to constrain the vertical and horizontal wavelengths of the observed waves.