EPSC Abstracts
Vol. 19, EPSC2026-57, 2026, updated on 02 Jul 2026
https://doi.org/10.5194/epsc2026-57
Europlanet Science Congress 2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
Poster | Tuesday, 08 Sep, 18:00–19:30 (CEST), Display time Tuesday, 08 Sep, 08:30–19:30| Foyer 2, F2.55
An Objective Analysis Dataset for Long-Term Variability of Venusian Super-Rotation Using Akatsuki Wind Assimilation
Yukiko Fujisawa1, Norihiko Sugimoto1, Nobumasa Komori1, Shin-ya Murakami2, Hiroki Ando3, Masahiro Takagi3, Takeshi Imamura4, Takeshi Horinouchi5, George L. Hashimoto6, Masaki Ishiwatari5, Takeshi Enomoto7, Takemasa Miyoshi8, Yasumitsu Maejima6, Hiroki Kashimura6, and Yoshi-Yuki Hayashi6
Yukiko Fujisawa et al.
  • 1Keio University, Yokohama, Japan
  • 2Japan Aerospace Exploration Agency, Sagamihara, Japan
  • 3Kyoto Sangyo University, Kyoto, Japan
  • 4The University of Tokyo, Kashiwa, Japan
  • 5Hokkaido University, Sapporo, Japan
  • 6Kobe University, Kobe, Japan
  • 7Kyoto University, Kyoto, Japan
  • 8RIKEN Center for Computational Science, Kobe, Japan

The Venus orbiter Akatsuki has accumulated observational data over a long period from 2015 to 2024. Horizontal winds derived from cloud tracking using the onboard Ultraviolet Imager (UVI) have revealed that the super-rotation speed exhibits both faster and slower phases (Horinouchi et al., 2024) [1].

Fujisawa et al. (2022) [2] produced an objective analysis dataset of the Venusian atmosphere by assimilating horizontal winds derived from Akatsuki observations using the Venus general circulation model AFES-Venus (Sugimoto et al., 2014) [3] and the data assimilation system ALEDAS-V (Sugimoto et al., 2017) [4]. This dataset successfully corrects the phase bias of thermal tides and the super-rotation speed (zonal-mean zonal wind) in AFES-Venus, bringing them closer to observations of the real Venusian atmosphere. The dataset was constructed by assimilating observations from September to December 2018, including an intensive observation period of Akatsuki.

In this study, we selected five epochs with characteristic super-rotation speeds during the long-term observation period of Akatsuki and constructed objective analysis datasets for each epoch. The figure shows the latitudinal distribution of the zonal-mean zonal wind near the cloud-top altitude (~69 km). Solid lines indicate the objective analysis, while dashed lines represent observations. Compared with the free run forecast without data assimilation (FRF), the super-rotation speeds in all epochs are substantially reduced when observational data are assimilated. Furthermore, the reproduced wind fields show good agreement with observations, including the meridional asymmetry. These results demonstrate that the data assimilation system successfully reproduces the observed wind structures. The resulting objective analysis datasets are expected to be useful for investigating the mechanisms underlying the long-term variability of Venusian super-rotation.

 

[1] Horinouchi, T., et al. (2024) J. Geophys. Res. Planets 129, e2023JE008221.

[2] Fujisawa, Y., et al. (2022) Sci. Rep. 12, 14577.

[3] Sugimoto, N., et al. (2014) J. Geophys. Res. Planets 119, 1950–1968.

[4] Sugimoto, N., et al. (2017) Sci. Rep. 7(1), 9321.

 

How to cite: Fujisawa, Y., Sugimoto, N., Komori, N., Murakami, S., Ando, H., Takagi, M., Imamura, T., Horinouchi, T., Hashimoto, G. L., Ishiwatari, M., Enomoto, T., Miyoshi, T., Maejima, Y., Kashimura, H., and Hayashi, Y.-Y.: An Objective Analysis Dataset for Long-Term Variability of Venusian Super-Rotation Using Akatsuki Wind Assimilation, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-57, https://doi.org/10.5194/epsc2026-57, 2026.