Dissipation mechanisms for convection in rapidly rotating spheres and the formation of banded structures

We report banded zonal structures in numerical simulations of weakly nonlinear rapidly rotating convection. A quasigeostrophic model of convection is used to demonstrate how, in the presence of Ekman pumping, banded structures can develop immediately above the onset of convection, and in the absence of developed turbulence. We argue that these bands necessarily correspond to a regime in which both Ekman pumping and bulk viscosity equally affect the zonal flow and that their width scales with the Ekman number E as E-1/4.