Geostrophic motions of a Boussinesq fluid in a thick rotating spherical shell

We investigate numerically the three-dimensional flow in a thick spherical shell, when a Boussinesq fluid is subject to an internal isotropic heat sou rce and to an external differential heating. The external heat source is a model of the solar heating and, therefore, varies with the inclination of t he rotation axis of the system. The conductive temperature field consistent with the thermal forcing is first analyzed and then the flow compatible wi th this temperature held is computed. It is shown that, for moderate therma l forcings, the flow is axisymmetric and geostrophic. Two Hadley cells deve lop on each side of the equator, from the equator to the poles. The flow ex tends throughout the whole layer, but the heat and angular momentum transfe rs are essentially diffusive, due to the weakness of the flow. Energy and a ngular momentum are conserved at a good approximation. The parameters intro duced in the simulations were chosen to be relevant to the known characteri stics of the outer planets.