Influences of Venus’ topography on fully developed superrotation and near-surface flow

Abstract

We investigate the influence of topography on Venus' atmospheric general circulation. Based on comparative simulations with and without the Venusian topography, we elucidate the role of the topography in the fully developed superrotation. Orographically forced stationary waves are predominant over Mt. Maxwell: slightly weakening the superrotation near the cloud top. Differently from previous GCM results, the orographically forced waves do not produce significant asymmetry between the northern and southern hemispheric superrotations in the present model. Weak surface flows from mountains to lowlands are caused by the pressure dependence of the Newtonian cooling. The pattern and magnitude of the near-surface flow are largely different from those simulated in the Herrnstein and Dowling (2007) model. This implies that the parameterizations of physical processes (such as Newtonian cooling, turbulence, diffusion, and surface drag) and the model resolution could significantly influence the pattern and magnitude of the near-surface flow and the orographical forcing of planetary-scale stationary waves.

Atmospheric response to high-resolution topographical and radiative forcings in a general circulation model of Venus: Time-mean structures of waves and variances

“…The zonal-flow increase caused by the topography in the T63 simulation above the cloud top supports the results of Lebonnois et al (2010) , who reported that the zonal flow in the presence of topography is faster than that under the flat-surface condition around 70 km. Such a topographical enhancement of the superrotational flow is not seen in the T21 experiments of Yamamoto and Takahashi (2009) and Yamamoto et al (2019) , in which the topography does not increase the zonal-flow speed above the cloud top. The topography in our T63 experiment intensifies the poleward flow ( ) of the Hadley cell above the 10 3 -Pa altitude (>75 km) and vertically-thin Hadley circulation around 10 5 Pa.…”

“…In contrast, Lebonnois et al (2010) showed an increase in the superrotation and no significant asymmetry in the presence of the topography. In the T21 AGCMs of Yamamoto and Takahashi (2009) ; Yamamoto et al (2019) , the topography slightly weakens the superrotation and does not produce a significantly asymmetric structure in the general circulation. At the present stage, the effects of high-resolution topography on the dynamics (e.g., general circulation, longitudinal wind variation, and the global-scale bow-shaped wave) have not been fully understood.…”

“…Recent satellite-based observations have shown a conspicuous variation of the zonal flow ( Bertaux et al, 2016 ) and global-scale stationary bow-shaped waves ( Fukuhara et al, 2017 ) over the Aphrodite Terra. GCM simulations with topography have been conducted in previous works ( Herrnstein and Dowling, 2007 ; Yamamoto and Takahashi, 2009 ; Lebonnois et al, 2010 , Lebonnois et al, 2018 ; Navarro et al, 2018 ; Yamamoto et al, 2019 ). As reviewed in Sánchez-Lavega et al (2017) , the effects of Venus' surface topography on superrotation vary considerably with model.…”

The distribution of carbon monoxide in the lower atmosphere of Venus

“…Above the orography deficient southern mid-to polar-latitudes, zonally propagating gravity waves have been identified at the top of this layer (~47 km) with horizontal wavelengths in the range 60 to 150 km (Peralta et al, 2008). Modeling studies (Yamamoto and Takahashi, 2009) also predict orographically forced planetary-scale stationary waves corresponding to the latitude of Ishtar Terra, with smaller scale waves corresponding to Aphrodite Terra, at altitudes below 65 km and 50 km respectively. If such planetary-scale structures are present in the lower atmosphere we might expect them to influence the pattern of CO concentration in an observable way.…”