AKATSUKI data assimilation

Comprehensive picture of atmospheric circulation of Venus revealed by AKATSUKI data assimilation
This research is supported by JSPS Grant-in-Aid for Scientific Research (S), 19H05605 (2019.6-2024.3).


Background and objectives

Circulation structure of Venus atmosphere have not been understood well. In particular, structure of lower atmosphere of Venus has not been revealed because of the existence of thick cloud layer around 45-70 km altitude. The most prominent feature of the Venus atmospheric circulation is the "superrotaion (4-day circulation)", i.e., fast zonal wind whose velocity reaches about 100 m/s at the top of cloud layer. The velocity is tens of times faster than rotation speed of solid body of Venus. This superrotation is maintained by angular momentum transfer from solid body of Venus to its atmosphere, but the circulation associated with it has not been revealed and is a basic question of meteorology.

Under the situation, a Japanese spacecraft "Akatsuki" was successfully inserted into an orbit around Venus, and has been observing Venus by the use of four cameras. These four cameras probe different levels of Venus atmosphere. Before Akatsuki observation, data on Venus atmosphere were sparse, and, on the other hand, simulation models of Venus atmosphere was not established beacuse of lack of observation on circulation structure.

However, surprising similarities have been shown between clear images observed by "Akatsuki" and simulation results of a high resolution Venus general circulation model (AFES-Venus) (Figure 1). This implies that comparison between observation and model is possible. The objectives of our research is to approach mysteries of circulation structure of Venus atmosphere, i.e. superrotation, by achieving comparison between model and observation with the aid of the state of the art methods.

Figure 1


We will produce a circulation field of Venus atmosphere which is consistent with observations in dynamical context. This is achieved by combining observational data by "Akatsuki" and simulation data by AFES-Venus by the use of "data assimilation" technique. This will be advanced further based on future observations desigined by "Akatsuki" observation simulation by the use of radio occultation observation, camera images, and wind vectors deduced by cloud tracking, and simulations by a model which includes cloud and radiative processes.

Figure 2


Related Links

Akatsuki DA wiki (access restricted)