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

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.