The puzzling Venusian polar atmospheric structure reproduced by a general circulation model

Abstract

Unlike the polar vortices observed in the Earth, Mars and Titan atmospheres, the observed Venus polar vortex is warmer than the midlatitudes at cloud-top levels (∼65 km). This warm polar vortex is zonally surrounded by a cold latitude band located at ∼60° latitude, which is a unique feature called ‘cold collar' in the Venus atmosphere. Although these structures have been observed in numerous previous observations, the formation mechanism is still unknown. Here we perform numerical simulations of the Venus atmospheric circulation using a general circulation model, and succeed in reproducing these puzzling features in close agreement with the observations. The cold collar and warm polar region are attributed to the residual mean meridional circulation enhanced by the thermal tide. The present results strongly suggest that the thermal tide is crucial for the structure of the Venus upper polar atmosphere at and above cloud levels.

Local Time Dependence of the Thermal Structure in the Venusian Equatorial Upper Atmosphere: Comparison of Akatsuki Radio Occultation Measurements and GCM Results

“…In the present study, we compare the radio occultation measurements with GCM simulations to understand the atmospheric dynamics of the observational results. A Venus GCM used in this study is AFES‐Venus, a full nonlinear GCM with simplified physical processes for the Venus atmosphere (Sugimoto et al, , ), which has enabled us to reproduce the realistic zonal wind and temperature distributions of the Venus atmosphere (Sugimoto et al, ), the unique polar atmospheric structure such as the cold collar and warm polar regions (Ando et al, ), and short‐period temperature disturbances observed in the warm polar region (Ando et al, ). Recently, Sugimoto et al () succeeded in data assimilation by using the wind field data obtained in Venus Express mission.…”

“…In this study, we analyze the Akatsuki radio occultation data to investigate the local time dependence of the thermal structure of the upper atmosphere in the equatorial region and compare the results with numerical simulations by a Venus GCM. The GCM used in this study is a full nonlinear Venus GCM named AFES‐Venus (Ando et al, , ; Sugimoto et al, , ; Takagi et al, ), based on AFES 2 (Atmospheric GCM for the Earth Simulator version 2; Enomoto et al, ; Ohfuchi et al, ).…”

Vertical structure of the axi‐asymmetric temperature disturbance in the Venusian polar atmosphere: Comparison between radio occultation measurements and GCM results

“…Since in our model the planet Venus is assumed to rotate toward the same direction as the Earth, note that the zonal wind (superrotation) reproduced in our model also directs toward the east. Details of the model settings are described in Sugimoto et al [] and Ando et al [].…”

“…Since in our model the planet Venus is assumed to rotate toward the same direction as the Earth, note that the zonal wind (superrotation) reproduced in our model also directs toward the east. Details of the model settings are described in Sugimoto et al [2014b] and Ando et al [2016]. The model atmosphere reached quasi-steady states within approximately 1 Earth year, and the quasi-steady states were maintained for more than 10 Earth years [Sugimoto et al, 2014b].…”

“…This may be related to the 5 day wave observed at the cloud top [ Del Genio and Rossow , ]. Ando et al [] investigated the polar region of the Venusian middle atmosphere by using AFES‐Venus and found that the cold collar and the warm polar region are successfully reproduced in the numerical results. They pointed out that these features observed in the Venusian polar region are strongly related with the residual mean meridional circulation intensified by the thermal tide.…”