Modeling of zonal flows on gas giants and ice giants - A unified approach using 3D compressible model

Cloud top zonal flows are generally observed on the four solar giant planets: prograde equatorial jets are observed on the “traditional” gas giants, Jupiter and Saturn; whereas those of the icy giants, Uranus and Neptune, are found to be retrograde. Previous studies have used models of three-dimensional (3D) Boussinesq convection in a rotating spherical shell to explain the zonal flows of both cases. In this paper we present an alternative model of 3D compressible flow in the rotating spherical shell, implemented in spectral transform method, which exhibits good stability in a wide range of shell parameters (e.g. shell thickness, viscosity and rotation rate). We also demonstrate that upon variation of the shell thickness, the zonal flow generally shows a directional transition from prograde in thick shells, to retrograde in thin ones. The results suggest that the different planetary zonal flows may be explained by a similar process. The different types of mean flows reflect different convection zone depths (as the rotation rates of these planets are within a factor of 2).