JpGU-AGU Joint Meeting 2020

Presentation information

[E] Poster

A (Atmospheric and Hydrospheric Sciences ) » A-OS Ocean Sciences & Ocean Environment

[A-OS21] Dynamics of oceanic and atmospheric waves, vortices, and circulations

convener:Yuki Tanaka(Fukui Prefectural University), Ryo Furue(APL/JAMSTEC), Yukiharu Hisaki(University of the Ryukyus), Norihiko Sugimoto(Keio University, Department of Physics)

[AOS21-P01] Data Assimilation of the Venus Atmosphere to Reproduce Planetary-scale Wave

*Yukiko Fujisawa1, Mimo Shirasaka2, Norihiko Sugimoto1, Asako Hosono3, Mirai Abe1, Hiroki Ando4, Masahiro Takagi4, Masaru Yamamoto5 (1.Keio University, 2.Seisen Senior High School, 3.Toshimagaoka Women High School, 4.Kyoto Sangyo University, 5.Research Institute for Applied Mechanics, Kyushu University)

Keywords:Data assimilation, Venus atmosphere, Planetary-scale Wave

Planetary scale waves with about a 4-day period, which are considered to be “Kelvin waves”, have been observed in the equatorial region at the cloud top of the Venus atmosphere1,2. It is pointed out that these Kelvin waves could contribute to generate and maintain the atmospheric “super rotation”: the zonal wind circulating Venus 60 times faster than the solid part of Venus3. However, the Kelvin waves have not been simulated so far in any Venusian Atmospheric General Circulation Model (AGCM) in the world.

We have developed a Venusian GCM (AFES-Venus), and the Venus AFES LETKF Data Assimilation System (VALEDAS) based on the Local Ensemble Transform Kalman Filter (LETKF) for the first time4,5. Using VALEDAS, 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 temperature observations by multiple small satellites6.

In this study, we prepared an idealized horizontal wind observation that was expected to be obtained from cameras with various wavelengths, and examined the reproducibility of Kelvin wave by varying conditions such as observation altitude, observation area, and time interval. The idealized observation data are created from CCSR/NIES Venus AGCM7, in which the Kelvin wave was reproduced by forcing it at a lower level.

Fig (a) shows result of a free run forecast (without observation), and (b) shows assimilated result of horizontal wind observation at the altitude of 30 km with 24 hourly. By the data assimilation, the upper propagation of waves with a period of about 5 days at the equator was reproduced. We will also discuss how the observation and this kind of study would be helpful to design the future mission for understanding of Venus.

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[2] Planetary-scale wave and the cyclic nature of cloud top dynamics on Venus. A. D. Del Genio and W. B. Rossow, J. Atmos. Sci. 47, (1990), p293–318.
[3] Formation and maintenance of the 4-day circulation in the Venus middle atmosphere, M. Yamamoto and H. Tanaka, J. Atmos. Sci., 54, (1997), p1472-1489.
[4] Baroclinic modes in the Venus atmosphere simulated by GCM, N. Sugimoto, M. Takagi, and Y. Matsuda, Journal of Geophysical Research: Planets, Vol. 119, (2014), p1950–1968, doi:10.1002/2014JE004624.
[5] 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.
[6] 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, (2019).
[7] Venusian middle-atmospheric dynamics in the presence of a strong planetary-scale 5.5-day wave, M. Yamamoto and M. Takahashi, Icarus, (2012), 217, p702-713.