Abstract
Infrared and radio observations of the upper cloud region of Venus indicate that the north polar region contains Features of large thermal contrast. A cold collar, encompassing a region of temperature inversions, lies between latitudes of ∼65 and 75°C, and a pair of warm features, separated by ∼180° of longitude and centered near 80° latitude, rotate about the pole with a period of ∼2.9 days. It is shown that the cold temperatures associated with the inversions lead to an enhancement in the mean zonal wind in a localized area near the pole, and that this enhancement makes the mean flow barotropically unstable. Since data for this region are limited a model for the thermal structure has been used for calculating growth times and phase periods of the unstable modes. Choosing model parameters to agree as closely as possible with available data, it has been determined that the rotating warm features are likely to be manifestations of barotropically unstable waves.
