Turbulent Convection in an Anelastic Rotating Sphere: A Model for the Circulation on Gas Giant Planets

Yohai Kaspi, Ph.D., 2008
Glenn Flierl, Advisor

This thesis studies the dynamics of a rotating compressible gas sphere, driven by internal convection, as a model for the dynamics on the giant planets. We develop a new general circulation model for the Jovian atmosphere, based on the MITgcm dynamical core augmenting the nonhydrostatic model. The grid extends deep into the planet's interior allowing the model to compute the dynamics of a whole sphere of gas rather than a spherical shell (including the strong variations in gravity and the equation of state). Dierent from most previous 3D convection models, this model is anelastic rather than Boussinesq and thereby incorporates the full density variation of the planet. We show that the density gradients caused by convection drive the system away from an isentropic and therefore barotropic state as previously assumed, leading to signicant baroclinic shear. This shear is concentrated mainly in the upper levels and associated with baroclinic compressibility effects. The interior ow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy uxes, generating the observed equatorial superrotation. We also use simpler models: a barotropic annulus model, and a quasi- geostrophic baroclinic model to study dynamical mechanisms seen in the convection model.