Cold Collar Reproduced by a Venus GCM With the Akatsuki Horizontal Wind Assimilation

The thermal structure of the upper atmosphere in the Venus polar region is reproduced by the assimilation of horizontal winds in low- and mid-latitudes derived from the Akatsuki ultra-violet images. The obtained structure is well consistent with infrared and radio occultation measurements. In particular, the unique thermal features in the Venus polar vortex such as the cold collar and the warm polar region in our model are realistic: the level where the cold collar is located and the temperature difference between the cold collar and the warm polar region are consistent with data. The reasons why the thermal structure of the upper atmosphere in the Venus polar region is realistic are that the zonal wind distribution around the cloud top level and the structure of the residual mean meridional circulation induced by the thermal tides are improved with respect to the model without data assimilation. Our results also suggest that the thermal structure in the Venus upper polar region is closely related to the atmospheric dynamics.