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

Abstract

A quasi‐periodic variation of the lower cloud amount induced by atmospheric waves was reproduced in our Venus general circulation model for the first time. This result agrees well with previous 2.3‐μm infrared nightside measurements. The cloud amount variation is mainly caused by a temperature fluctuation with a period of ∼5.5 Earth days near the cloud base, which is associated with a Kelvin‐like gravity wave with a zonal wavenumber‐1 structure. Our result might be able to explain the mechanism of the periodical variation of the brightness in the Venusian low‐latitudes shown by the previous 2.3‐μm infrared nightside measurements. It is also suggested that the temporal variation of the mass loading due to the temperature fluctuation is related to the abrupt appearance and disappearance of the large cloud particle (Mode 3) and explains the sharp discontinuity of the lower cloud found by the recent Akatsuki and ground‐based infrared nightside measurements.

A GCM Study on the 4‐Day and 5‐Day Waves in the Venus Atmosphere

“…(2020) and Ando et al. (2021), small‐scale disturbances with large vertical winds were predominant at 50 km levels and the vertical winds associated with the planetary‐scale Kelvin‐like waves were not isolated. The present result suggests that the lower clouds could be also affected by the Kelvin modes associated with the 5.8‐day and 4.8‐day waves.…”

“…On the other hand, Ando et al. (2021) showed that the lower clouds are mainly affected by temperature deviations associated with Kelvin‐like gravity waves trapped at the cloud bottom levels, using a Venus GCM with a simple cloud model. However, there are significant differences in the wave structures in these studies.…”

“…Peralta et al (2020) suggested that the lower clouds are mainly affected by vertical winds associated with nonlinear Kelvin waves, which propagate vertically in the cloud bottom levels. On the other hand, Ando et al (2021) showed that the lower clouds are mainly affected by temperature deviations associated with Kelvin-like gravity waves trapped at the cloud bottom levels, using a Venus GCM with a simple cloud model. However, there are significant differences in the wave structures in these studies.…”

“…Hosouchi et al (2012) also pointed out that planetary-scale waves with a zonal wavenumber of 1 and a period of 4.9 days exist in the equatorial region at 58-64 km altitudes. Recent numerical studies with the GCMs suggest that the lower clouds in low latitudes could be strongly affected by planetary-scale Kelvin-like waves (Ando, Takagi, et al, 2020;Ando et al, 2021;Peralta et al, 2020) though the characteristics of these waves remain unclear.…”

Vertical‐Wind‐Induced Cloud Opacity Variation in Low Latitudes Simulated by a Venus GCM

“…The obtained trend of the zonal mean cloud distribution was consistent with the past observation (Haus et al, 2014), although the cloud top altitude was the highest in high latitudes. The subsequent work by Ando et al (2021) investigated the temporal and spatial variation of the clouds in low latitudes and reported that the temperature variation associated with the Kelvin-like gravity wave causes the quasi-periodic cloud variation similar to that reported by Crisp et al (1991). They suggested that the temperature variation changes H 2 SO 4 saturation vapor pressure, and cloud condensation/evaporation occurs near the cloud base.…”