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We study rapidly-rotating Boussinesq convection driven by internal heating ina full sphere. We use a numerical model based on the quasi-geostrophicapproximation for the velocity field, whereas the temperature field isthree-dimensional. This approximation allows us to perform simulations forEkman numbers down to 1e-8, Prandtl numbers relevant for liquid metals (~0.1)and Reynolds numbers up to 3e4. Persistent zonal flows composed of multiplejets form as a result of the mixing of potential vorticity. For the largestRayleigh numbers computed, the zonal velocity is larger than the convectivevelocity despite the presence of boundary friction. The convective structuresand the zonal jets widen when the thermal forcing increases. Prograde andretrograde zonal jets are dynamically different: in the prograde jets (whichcorrespond to weak potential vorticity gradients) the convection transportsheat efficiently and the mean temperature tends to be homogenised; by contrast,in the cores of the retrograde jets (which correspond to steep gradients ofpotential vorticity) the dynamics is dominated by the propagation of Rossbywaves, resulting in the formation of steep mean temperature gradients and thedominance of conduction in the heat transfer process. Consequently, inquasi-geostrophic systems, the width of the retrograde zonal jets controls theefficiency of the heat transfer.

Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores