Assimilation of the temperature derived by Akatsuki Longwave Infrared Camera in the Venus atmosphere

Data assimilation of the Venus atmosphere has become more feasible due to the long-term observations by the Venus climate orbiter “Akatsuki”. We have produced the first objective analysis for the Venus atmosphere by assimilating horizontal winds derived by the cloud tracking of the Akatsuki Ultraviolet Imager (UVI) [1]. Here, we assimilate the temperature derived by the Akatsuki Longwave Infrared Camera (LIR), using the AFES-LETKF data assimilation system for Venus "ALEDAS-V" [2], which is based on the atmospheric general circulation model for Venus "AFES-Venus" [3] and local ensemble transform Kalman filter “LETKF”. In this experiment the altitude for the assimilation is set to 65 km regardless of the emission angle for simplicity, though the altitude observed by LIR depends on the emission angle (the angle between the zenith and observer directions as seen from the observation point). The influence of the emission angle is investigated for two cases; the one is the emission angle limited to 40 degrees or less and the other one is that limited to 75 degrees or less.

 

[1] Fujisawa, Y., Sy. Murakami, N. Sugimoto, M. Takagi, T. Imamura, T. Horinouchi, G. L. Hashimoto, M. Ishiwatari, T. Enomoto, T. Miyoshi, H. Kashimura and Y.-Y. Hayashi, Y.-Y. (2022), Sci. Rep. 12, 14577.

[2] Sugimoto, N., A. Yamazaki, T. Kouyama, H. Kashimura, T. Enomoto, and M. Takagi (2017), Sci. Rep., 7(1), 9321.

[3] Sugimoto, N., M. Takagi, and Y. Matsuda (2014a), J. Geophys. Res. Planets, 119, 1950–1968.