Mean zonal flows excited by critical thermal convection in rotating spherical shells

Mean zonal flows excited by critical modes of Boussinesq convection in rotating spherical shells are evaluated systematically by the weak nonlinear method. Calculations are executed in the ranges of the Prandtl number 0.01≤P≤102, the Taylor number 100≤T≤107, and the radius ratio 0.2≤η≤0.8. In the case of small rotation rates, two new states of zonal flow at the equatorial outer boundary are obtained; westerly flow emerges even when the Prandtl number is large, and easterly flow emerges even when the Prandtl number is small. The latter case is interesting since the induced equatorial easterly is in the opposite direction to that of the acceleration. In the case of large rotation rates, it is confirmed that the direction of mean zonal flow at the equatorial outer boundary does not depend on the thickness of the shell.