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

TL;DR

This paper reports the discovery of a long-lived, sharp atmospheric disruption on Venus's lower clouds, characterized by a rapid westward rotation and recurrent over decades, likely caused by a nonlinear Kelvin wave.

Contribution

It provides the first detailed observation of a persistent, sharp disruption in Venus's lower clouds and links it to a nonlinear Kelvin wave through numerical simulations.

Findings

Disruption exhibits a ~4.9-day westward rotation period.

Disruption remains coherent for weeks and is recurrent since 1983.

Numerical models suggest a nonlinear Kelvin wave explains its properties.

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$^{\circ}$N--40$^{\circ}$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 $\sim$4.9 days faster than winds at this level ($\sim$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.