Abstract
At the cloud top of the Venus atmosphere, equatorial Kelvin waves have been observed and are considered to play an important role in the super-rotation. We were able to reproduce the wave in a general circulation model (GCM) by conducting an observing system simulation experiment (OSSE) with the help of a data assimilation system. The synthetic horizontal winds of the Kelvin wave produced by the linear wave propagating model are assimilated at the cloud top (~70 km) in realistic conditions, assuming they are obtained from cloud tracking of ultra-violet images (UVI) taken by the Venus orbiters. It is demonstrated using Eliassen–Palm (EP) fluxes that the reproduced Kelvin wave transports angular momentum and plays an important role in the magnitude and structure of the super-rotation, causing the acceleration and deceleration of zonal wind of ~0.1 m/s day−1. The conditions required in order to reproduce the Kelvin wave have also been investigated. It is desirable to have 24 hourly dayside satellite observations in an equatorial orbit, such as the Akatsuki Venus climate orbiter. The results of this type of data assimilation study will be useful in the planning of future observation missions to the atmospheres of planets.
Highlights
Venus is covered by a thick cloud at altitudes of around 45–70 km, and it is difficult to observe the atmosphere below the cloud from space directly
Horizontal winds obtained at the cloud top (70 km) in this model are used for data assimilation, by which the Kelvin wave with a period of ~4 Earth days is induced in the equatorial region
In order to confirm when the Kelvin wave is clearly reproduced during the time evolution of observing system simulation experiment (OSSE), longitude-time cross-sections of the zonal wind deviation from its time average at the equator and 70 km altitude are shown in Figure 2 for the (a) frf and (b) control cases
Summary
Venus is covered by a thick cloud at altitudes of around 45–70 km, and it is difficult to observe the atmosphere below the cloud from space directly. The Kelvin wave in the equatorial region propagates faster than the super-rotation, with a fast zonal flow of ~100 m/s at the cloud top, e.g., [5,6], with a period of ~4 Earth days, while the Rossby wave in mid-latitudes does slower with a period of ~5 Earth days [7,8]. As an extension of the previous study [12], here, we will reproduce the Kelvin wave more realistically and completely by the OSSE using ALEDAS-V and investigate its impact on the Venus atmosphere.
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