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

Mean zonal flows excited by critical modes of Boussinesq convection in rota ting spherical shells are evaluated systematically by the weak nonlinear me thod. Calculations are executed in the ranges of the Prandtl number 0.01 le ss than or equal to P less than or equal to 10(2), the Taylor number 10 deg rees less than or equal to T less than or equal to 10(7), and the radius ra tio 0.2 less than or equal to eta less than or equal to 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 ro tation 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.