Venusian Cloud Distribution Simulated by a General Circulation Model

Abstract

We construct a simple cloud model for a Venus general circulation model (GCM), which includes condensable gases of H2O and H2SO4 vapors, and condensation, evaporation, and sedimentation of sulfuric acid cloud particles. The zonally averaged mass loading of the cloud reproduced in the model takes its maximum and minimum in high and middle latitudes, respectively. This latitudinal distribution is consistent with the infrared measurements. The thick cloud is formed in high latitudes at 43–55 km altitudes by vertical winds associated with disturbances enhanced in the low static stability layer. The moderately thick cloud in low latitudes is attributed mainly to the transport of H2SO4 vapor by the mean meridional circulation. The horizontal cloud distribution in low latitudes has zonal wave numbers 1 and 2 structures, which change in time significantly. These characteristics of the low‐latitude cloud would be associated with atmospheric waves in the cloud layer. The mixing ratio of H2O vapor increases with latitude in the cloud layer due to the vertical wind disturbances in the low static stability layer in high latitudes. This latitudinal trend is qualitatively consistent with the infrared measurements. The mixing ratio of H2SO4 vapor increases with latitude in the subcloud layer because a large amount of the cloud is evaporated there due to the sedimentation of cloud particles in the thick lower cloud in the polar region. The present results suggest that the Venus cloud distribution in the lower cloud layer is strongly affected by waves and/or disturbances as well as the mean meridional circulation.

Quasi‐Periodic Variation of the Lower Equatorial Cloud Induced by Atmospheric Waves on Venus

“…Figure 7a suggests that the cloud is mainly produced (evaporated) in a region at 44–48 km altitudes where the temperature is decreasing (increasing). Because H 2 SO 4 vapor around the cloud base is almost saturated (Ando, Takagi, et al., 2020), the variation of the saturation mixing ratio of H 2 SO 4 vapor due to the increasing (decreasing) temperature induces the evaporation (condensation) of cloud particles near the cloud base. As a result, the zonal wavenumber‐1 cloud distribution is maintained by the temperature anomaly associated with the Kelvin‐like gravity wave.…”

“…(2020). H 2 O vapor is supplied by atmospheric motions from the lower atmosphere below 30 km altitude where its mixing ratio is fixed to be 30 ppmv (Imamura & Hashimoto, 1998; Hashimoto & Abe, 2001; Ando, Takagi, et al., 2020). We solve the mixing ratios of cloud and cloud materials (H 2 O and H 2 SO 4 vapors).…”

“…According to Knollenberg and Hunten (1980), it is assumed that the number densities of Mode 1 and Mode 2 particles are 1,000 cm −3 above 58 km altitude and 100 cm −3 below the level, respectively. The mean sedimentation velocity, W mean , is evaluated as follows (Ando, Takagi, et al., 2020): where ρ i and W i ( i = 1, 2) are the mass density and sedimentation velocity of Mode i , respectively. The sedimentation velocity of each mode cloud particle is given by the Stokes velocity (e.g., Ando, Takagi, et al., 2020; Imamura & Hashimoto, 1998).…”

“…Recently, Ando, Takagi, et al. (2020) constructed a simple cloud model for a Venus GCM named AFES‐Venus. This cloud model includes condensable gases of H 2 O and H 2 SO 4 , and condensation, evaporation, and sedimentation of sulfuric acid cloud particles.…”

Stratospheric Venus Observatory

“…Unlike a spacecraft in orbit around Venus, SVO is recoverable and can be re-lown every 19 months during Venus inferior conjunctions. SVO corrects some of the observing de iciencies of Venus Express (cloud tracking restricted to the southern hemisphere every 24 hours) and Akatsuki (no spectral capabilities), and SVO's nearly continuous time domain coverage is well-suited to provide data for assimilation into GCMs that have been developed in response to Venus Express and Akatsuki observations (e.g., [10]).…”