Interpretation of Thompson's Mechanism for Venus' Atmospheric Super-Rotation and its Extension to the Spherical Geometry

Abstract

Thompson's mechanism is reconsidered in a two-dimensional plane. It is shown that a mean shear flow can be generated by the positive feedback of a mean shear flow, tilting convective motion and tilting temperature distribution. In this instability, a small perturbation of mean shear flow tilts the basic temperature distribution. The tilting temperature distribution induces tilting of convective motion, which transports horizontal momentum vertically so as to reinforce the mean flow shear.
In order to examine the validity of Thompson's mechanism on the sphere, a three-dimensional nonlinear numerical model is constructed. Steady solutions which represent convection between the day and night sides on the sphere, are numerically obtained for various values of parameters, and their stability is examined. It is shown that, if the planetary rotation is neglected, three-dimensional convection on the sphere is stable and a mean shear flow cannot be generated. This result suggests that Thompson's mechanism proposed for two-dimensional convection cannot be applied to three-dimensional convection on the sphere.