The influence of seasonal cycles on superrotation

We explore the influence of the seasonal cycle on the maintenance of superrotation in terrestrial atmospheres. Previous work with has suggested the transition to superrotation occurs for thermal Rossby numbers larger than unity. The atmospheres of Titan and Venus meet this criterion, although Titan also experiences a pronounced seasonal cycle. We explore the influence of that cycle by introducing a non-dimensional parameter that externally controls the thermal inertia of the climate system. A large seasonal cycle tends inhibit atmospheres with large thermal Rossby numbers from developing superrotation by (1) cross-equatorial advection of low-angular-momentum air by the Hadley circulation and (2) the production of hemispherically asymmetric zonal winds. The latter may relate to a necessary condition for the global instability. Several other dynamical conditions are tested against superrotation in the simulations. The atmospheres of Earth, Mars and Titan are discussed in the context of these dynamical conditions, the Rossby numbers of their circulation, and the thermal inertias of their climates.