An Idealized Dynamical Model of General Terrestrial Atmospheres: From Earth Towards Venus

The parameter space of planetary atmospheric dynamics is high-dimensional, and until recent years was sparsely populated by only a handful of Solar System planets (including Earth) and moons. With the rapid rise in both the number of exoplanets and the range of their parameters observed, this space is beginning to be filled in. It hence becomes more meaningful to consider, and eventually to test, more general theories and models of planetary atmospheric dynamics, and how they vary, continuously or otherwise, with respect to these parameters.

In the present work we start from Earth, about whose atmosphere the most is known, and investigate the transition of an idealized terrestrial general circulation model towards Venus-like conditions, by varying the planetary rotation rate and surface atmospheric pressure (atmospheric mass or depth). Earth and Venus both have near-circular orbits and rapidly rotating atmospheres, and so we do not include seasonal time-dependence. Initially we consider a Held–Suarez-like thermal forcing. Equatorial superrotation is readily obtained, but the mean zonal wind seems remarkably sensitive to parameters, including the vertical lapse rate (and hence, potentially, to the presence of condensibles). To isolate the effect of eddies we compare fully-3D simulations with corresponding zonally symmetric simulations, and we assess gradient wind balance in a form appropriate to planets (such as Venus) whose winds (unlike Earth’s) are not slow compared to the planetary rotation velocity.