[P-PS06] Science of Venus: Venus Express, Akatsuki, and beyond

[PPS06-P12] Trials toward first Venus analysis product by data assimilation of Akatsuki observation

★Invited Papers

*Yukiko Fujisawa¹, Shin-ya Murakami², Norihiko Sugimoto¹, Masahiro Takagi³, Takeshi Imamura⁴, Takeshi Horinouchi⁵, George HASHIMOTO⁶, Masaki Ishiwatari⁵, Takeshi Enomoto⁷, Takemasa Miyoshi⁸, Yoshi-Yuki Hayashi⁹ (1.Keio University, 2.JAXA, 3.Kyoto Sangyo University, 4.Tokyo University, 5.Hokkaido University, 6.Okayama University, 7.Disaster prevention Research Institute, Kyoto University, 8.RIKEN, 9.Kobe University)

Keywords:Akatsuki, Venus atmosphere, Data assimilation

Observations of the Venus Orbiter "Akatsuki" provide us horizontal distributions of the horizontal wind derived from cloud tracking of the UVI camera images and of temperature observed by the LIR camera. However, these observations are very limited with respect to altitude, local time (day or night side), and frequency. It is difficult to elucidate general circulation including with various temporal and spatial scales only from observations. In this study, we aim to produce a Venus objective analysis that has high temporal and spatial resolutions by assimilating the Akatsuki observations into a general circulation model.

The model used in this study is a Venusian GCM (AFES-Venus) and the Venus AFES LETKF Data Assimilation System (ALEDAS-V) based on the Local Ensemble Transform Kalman Filter (LETKF) that has been developed for the first time¹. Using ALEDAS-V, we have examined impact of data assimilation on thermal tides for the Venus Express wind observations². In addition, we have examined the reproducibility of a unique atmospheric structure so-called “cold collar”, a cold latitudinal band encircling the warm polar vortex at about 60–70 km altitudes, in order to elucidate the effects of fixed temperature observations by multiple small satellites³.

In this presentation, we will introduce results obtained for idealized data assimilation. One is for vertical profiles of temperature assuming radio occultation observation with realistic trajectory (Related to Hosono et al.⁴). The other is for distributions of horizontal wind assuming camera observation (Related to Fujisawa et al.⁵). These are necessary attempts before assimilating actual observation data. Furthermore, we will also introduce the results of assimilating actual Akatsuki observation data.

[1] Development of an ensemble Kalman filter data assimilation system for the Venusian atmosphere, N. Sugimoto, A. Yamazaki, T. Kouyama, H. Kashimura, T. Enomoto, and M. Takagi, Scientific Reports, Vol. 7, (2017), 9321, 9pp.
[2] Impact of data assimilation on thermal tides in the case of Venus Express wind observation, N. Sugimoto, T. Kouyama, and M. Takagi, Geophys. Res., Lett., Vol. 46, (2019), pp. 4573–4580.
[3] Observing system simulation experiment for radio occultation measurements of the Venus atmosphere among small satellites, N. Sugimoto, M. Abe, Y. Kikuchi, A. Hosono, H. Ando, M. Takagi, I. Garate-Lopez, S. Lebonnois and C. Ao, Journal of Japan Society of Civil Engineers A2: Applied Mechanics, Vol. 75, No.2, (2019), pp. I_477-I_486.
[4] The study for designing the future Venus atmosphere observing mission of radio occultation measurement among small satellites using data assimilation, A. Hosono, Y. Fujisawa, N. Sugimoto, M. Abe, Y. Kikuchi, T. Yamamoto, Y. Kawabata, S. Ikari, H. Ando, M. Takagi, I. G. Lopez, S. Lebonnois, C. Ao, JpGU, (2020), A-OS21.
[5] Data Assimilation of the Venus Atmosphere to Reproduce Planetary-scale Wave, Y. Fujisawa, M. Shirasaka, N. Sugimoto, A. Hosono, M. Abe, H. Ando, M. Takagi, and M. Yamamoto, JpGU, (2020), A-OS21.