Gigantic Vortices From Barotropic Instability Observed in the Atmosphere of Venus

Until recently, the lower to middle cloud region of Venus had been supposed to be dynamically quiet, accommodating nearly steady superrotating westward flow. However, observations of the regions by Akatsuki, the latest Venus orbiter operating since 2015, have revealed a variety of cloud features indicative of vortices and waves. Here we report another, and arguably the most conspicuous, example. Akatsuki's near-infrared imager IR2 captured gigantic vortices rotating cyclonically on 25 August 2016. By using winds estimated by cloud tracking, the feature is shown to be quantitatively consistent with barotropic instability. The size of the vortices (similar to 1,000 km) and their spacing (similar to 2,500 km) are more than several times greater than the vortex-like features reported previously from the observations of Venus, and they are also greater than the largest barotropic instability observed in the Earth's troposphere.