Convective Parameterization in a Jovian Shallow Water Model

A. P. Ingersoll (Caltech)

Understanding what maintains the zonal jets on the giant planets is a central problem in planetary meteorology. There is general agreement that random forcing at small scales can lead to steady zonal flows in a thin layer of fluid on a rapidly rotating sphere. And there is general agreement that, on Jupiter, convection provides the small-scale forcing. But published numerical experiments do not rely on theories of convection to define the forcing. Instead they use uniformly distributed random sources of vorticity or vertical velocity. In contrast, jovian convection seems to be confined to cyclonic regions, and is presumably associated with heat sources and condensation of water. Also, as described by Cho et al at this meeting, the numerical experiments do not give particularly realistic flows: In these experiments the zonal winds are not larger than the eddy winds; multiple jets are not stable; and the curvature of the zonal jet profile does not exceed beta. Our theory is based on simple notions about the physics of moist convection. It naturally accounts for the apparent convective activity of cyclonic regions. In the shallow water equations for a single isentropic layer meant to represent the cloud zone of Jupiter, the forcing appears as a source term in the mass balance equation: Radiation removes mass uniformly over large horizontal scales, and convection adds mass on small scales when the layer gets too thin. The next step, which we are actively pursuing, is to run some numerical experiments with this new, physically-based forcing. [This research was supported by the NASA Planetary Atmospheres Program and the Galileo Project.]