[P-PS04] Recent advances in the science of Venus

[PPS04-P10] Toward producing the Venus objective analysis using temperature obtained by Akatsuki Longwave Infrared Camera

*Yukiko Fujisawa¹, Norihiko Sugimoto¹, Nobumasa Komori¹, Hiroki Ando², Masahiro Takagi², Shin-ya Murakami³, Toru Kouyama⁴ (1.Keio University, 2.Kyoto Sangyo University, 3.JAXA, 4.AIST)

Keywords:Venus atmosphere, Data assimilation, Akatsuki

Data assimilation of the Venus atmosphere has become more feasible due to the long-term accumulation of observation data obtained from the Venus orbiter Akatsuki. Fujisawa et al. [1] produced the first objective analysis for Venus by assimilating horizontal winds obtained from cloud tracking with the Akatsuki Ultraviolet Imager. In this study, following on from [1], we use the Venus atmospheric data assimilation system "ALEDAS-V" [2], which is based on the Venus atmospheric general circulation model "AFES-Venus" [3] to assimilate the temperature obtained by the Akatsuki Longwave Infrared Camera (LIR), and attempt to produce the objective analysis for Venus. Although the altitude observed by LIR depends on the emission angle (the angle between the zenith direction and the observer direction as seen from the observation point), in this experiment, the assimilation altitude was set to 65 km altitude regardless of the emission angle for simplicity. We investigated the influence of the emission angle on assimilation by using observation data for two cases in which the emission angle was limited to 40 degrees or less and 75 degrees or less.

The figures show the latitudinal and vertical cross-sections of the temporal and zonal-mean zonal wind (color, m/s) and temperature (contour, K). In the experiment without assimilation (free run; Figure a), the super-rotation (zonal wind at around 70 km altitude) has a speed of about 130 m/s, which is faster than the speed observed so far (~100 m/s). In the assimilation of only observation data with the emission angle of 40 degrees or less (em40; Figure b), the speed of super-rotation comparable to that observed was obtained, and super-rotation was improved by assimilation. In addition, in order to include more observation data from mid-to-high latitudes, we assimilated only observation data with the emission angle of 75 degrees or less (em75; Figure c), and the slower super-rotation was obtained compared to observations. The reason may be that observation data with the high emission angle is assimilated to a different altitude than originally intended, and its observation data cause excessive warming of mid-to-high latitudes.

[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.