Observing System Simulation Experiment to Reproduce Kelvin Wave in the Venus Atmosphere

Abstract

Planetary-scale 4-day Kelvin-type waves at the cloud top of the Venus atmosphere have been reported from the 1980s, and their significance for atmospheric dynamics has been pointed out. However, these waves have not been reproduced in Venus atmospheric general circulation models (VGCMs). Recently, horizontal winds associated with the planetary-scale waves at the cloud top have been obtained from cloud images taken by cameras onboard Venus orbiters, which could enable us to clarify the structure and roles of Kelvin-type waves. In order to examine this possibility, our team carried out an idealized observing system simulation experiment (OSSE) with a data assimilation system which we developed. The wind velocity data provided by a CCSR/NIES (Center for Climate System Research/National Institute for Environmental Studies) VGCM where equatorial Kelvin-type waves were assumed below the cloud bottom was used as idealized observations. Results show that 4-day planetary-scale Kelvin-type waves are successfully reproduced if the wind velocity between 15° S and 15° N latitudes is assimilated every 6 h at 70 km altitude. It is strongly suggested that the Kelvin-type waves could be reproduced and investigated by the data assimilation with the horizontal wind data derived from Akatsuki ultraviolet images. The present results also contribute to planning future missions for understanding planetary atmospheres.

The first assimilation of Akatsuki single-layer winds and its validation with Venusian atmospheric waves excited by solar heating

“…In this study, we mainly focused on the thermal tide in the analysis for just one period. In the previous data assimilation test studies, it has been reported that the cold collar 49 and planetary-scale Kelvin waves 50 , 51 could be reproduced with sufficiently frequent observations. We are now planning to produce analyses with a number of observation periods, with which such kind of short period disturbances can be reproduced and investigated widely in the Venus research community.…”

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

“…They indicated that the cold collar is successfully reproduced by assimilating at least 2 or 3 vertical temperature profiles in the polar region every 4 or 6 hr. Recently, Sugimoto et al (2021) assimilated the horizontal wind associated with equatorial Kelvin-type waves which was artificially forced in the Venus GCM of Yamamoto and Takahashi (2012). As a result, they found that 4-day planetary-scale Kelvin-type waves could be reproduced when the horizontal wind in low-latitudes was assimilated every 6 hr at 70 km altitude.…”