A Long‐Lived Sharp Disruption on the Lower Clouds of Venus

Abstract

Planetary‐scale waves are thought to play a role in powering the yet unexplained atmospheric superrotation of Venus. Puzzlingly, while Kelvin, Rossby, and stationary waves manifest at the upper clouds (65–70 km), no planetary‐scale waves or stationary patterns have been reported in the intervening level of the lower clouds (48–55 km), although the latter are probably Lee waves. Using observations by the Akatsuki orbiter and ground‐based telescopes, we show that the lower clouds follow a regular cycle punctuated between 30°N and 40°S by a sharp discontinuity or disruption with potential implications to Venus's general circulation and thermal structure. This disruption exhibits a westward rotation period of ∼4.9 days faster than winds at this level (∼6‐day period), alters clouds' properties and aerosols, and remains coherent during weeks. Past observations reveal its recurrent nature since at least 1983, and numerical simulations show that a nonlinear Kelvin wave reproduces many of its properties.

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

“…This inconsistency might be attributed to the difference of the wave structures shown between in our model and in Peralta et al. (2020). Peralta et al.…”

“…Our results suggest that the relatively high optical thickness region shown by Peralta et al. (2020) is attributed to the abrupt creation of Mode 3 particle in the relatively low temperature region which is associated with the Kelvin‐like gravity wave at the cloud base in low‐latitudes.…”

“…In this study, we extend the work of Ando, Takagi, et al. (2020) to investigate how the cloud amount changes in time at low‐latitudes and compare the results with the infrared nightside measurements (e.g., Carlson et al., 1991; Crisp et al., 1991; Peralta et al., 2020).…”

“…Recently, Peralta et al. (2020) showed that the bright and dark regions with a zonal wavenumber‐1 structure at the lower cloud levels (48–55 km) are associated with a sharp disruption of the cloud morphology by analyzing infrared images obtained by Akatsuki IR1 and IR2 cameras and ground‐based telescopes. These features predominate at 40°S‐30°N latitudes and rotate with a period of ∼4.9 Earth days, faster than the super‐rotation.…”

Venus, an Astrobiology Target

“…On the night side, cloud opacity maps in the NIR also show the spatial and temporal evolution of the night-side cloud contrast (Limaye et al, 2018b;Peralta et al, 2019Peralta et al, , 2020. Comparison with concurrent thermal (brightness temperature) maps (e.g., Akatsuki Longwave InfraRed (LIR) camera data) with higher accuracy (>0.1 K) on the same spatial scale should reveal any patterns between the absorbed (day) and emitted radiation (night) and the contrasts in day-and night-side cloud cover.…”