Moist convection on gas giant planets simulated by a new global circulation model - planetMPAS

Convective storms on Jupiter and Saturn are ubiquitous features across the globe. These storms have sizes ranging from a few hundred kilometers to several thousand kilometers, and they are commonly recognized as a result of water moist convection due to large amount of latent heating associated with the water cycle. Recent Juno observations of Jupiter's polar cloud features revealed complex convective storm system that is very different from Saturn's polar dynamics. Previous numerical studies of moist convection on Jupiter and Saturn either focus on larger-scale dynamics with idealized physics parameterization of water cycle in a hydrostatic atmosphere, or mesoscale dynamics with detail microphysics in a non-hydrostatic atmosphere. This leads to a missing link between mesoscale dynamic system and planetary-scale dynamics. Here we developed a new global circulation model (GCM) for Jupiter and Saturn based on a state-of-the-art multiscale GCM, the Model for Prediction Across Scales (MPAS) that simulates fully compressible, non-hydrostatic atmospheres with mesoscale dynamics in a global domain. The MPAS's multiscale capability enables us to look into the detailed dynamical interactions between mesoscale and large-scale features, e.g., the polar dynamics on Jupiter and Saturn. The Jupiter MPAS and Saturn MPAS (as part of the planetMPAS suite) share several physics parameterizations, which include a turbulent mixing scheme that mixes vapor, heat, and momentum below cloud deck, a mass-flux-based moist convection scheme in the cloud layer, a simple microphysics scheme that represents the phase transition of water and conversion of cloud water/ice to rain/snow, and a Newtonian heating/cooling scheme (or radiative transfer scheme in a grey atmosphere) that mimics the solar radiation. In these two GCMs, convection on sub-grid scales are parameterized while those on grid scales are resolved by the dynamical core. Because of the uniformity of the unstructured grids and the scalability in terms of computation in MPAS, we are able to simulate the convective mesoscale dynamics in a global domain. Here we present our preliminary results that show the cloud dynamics and the interactions between moist convection and large-scale dynamics on Jupiter and Saturn.