[P-CG18] Planetary Magnetosphere, Ionosphere, and Atmosphere

[PCG18-10] Extraction of Martian atmospheric fine structures by analyzing Mars Global Surveyor radio occultation data

*Ryutaro Sakurai¹, Takeshi Imamura¹ (1.Graduate School of Frontier Sciences, The University of Tokyo)

Radio occultation observation is one of the most effective methods to study fine structures in planetary atmospheres. In order to derive the vertical structure of an atmosphere from the data of radio waves transmitted from the spacecraft and recorded at the ground station after passing through the planet's atmosphere, the geometric optics method has been used to calculate the ray path at each moment and then determine the atmospheric structure sequentially. In contrast, the recently developed radio holographic method derives the atmospheric structure from the entire signal time series at once, thereby significantly improving the vertical resolution compared to the geometric optics. One of the radio holographic methods, Full Spectrum Inversion (FSI) proposed by Jensen et al. (2003), was applied to the Venusian atmosphere by Imamura et al. (2018) to reveal fine vertical structures in the atmosphere that could not be captured by previous analysis.On Mars, the temperature structure of the Martian atmosphere has been obtained by radio occultation observations by Mars Global Surveyor (MGS). Various microstructures such as atmospheric gravity waves, convective boundary layers, and thin stable layers of ice clouds that occur at night have been revealed. Such fluid dynamical processes are thought to play important roles in the transport of energy and momentum. However, conventional analysis has an altitude resolution of about 1 km, which is not sufficient to fully resolve the vertical structures of these phenomena. The purpose of this study is to apply the new analysis method, FSI, to Martian radio occultation data in order to analyze the fine structures of the Martian atmosphere at a higher resolution than before, and to reveal the details of these small-scale processes.In this study, we analyzed the MGS radio occultation data by both the geometrical optics method and FSI, and compared the results. MGS conducted many radio occultations during its mission period from 1997 to 2006, and here we report results from a portion of the data. The atmospheric profiles obtained from MGS occultation data by geometrical optics method has already been released as an official product by the MGS project. However, since the geometrical optics analysis performed in this study shows finer structures, we will also report on the comparison between the two.