Diffusion-Free Scaling in Rotating Spherical Rayleigh-Benard Convection

Direct numerical simulations are employed to reveal three distinctly different flow regions in rotating spherical Rayleigh-Benard convection. In the high-latitude region I vertical (parallel to the axis of rotation) convective columns are generated between the hot inner and the cold outer sphere. The mid-latitude region II is dominated by vertically aligned convective columns formed between the Northern and Southern hemispheres of the outer sphere. The diffusion-free scaling, which indicates bulk-dominated convection, originates from this mid-latitude region. In the equator region III, the vortices are affected by the outer spherical boundary and are much shorter than in region II. Plain Language Summary Thermally driven turbulence with background rotation in spherical Rayleigh-Benard convection is found to be characterized by three distinctly different flow regions. The diffusion-free scaling, which indicates the heat transfer is bulk-dominated, originates from the mid-latitude region in which vertically aligned vortices are stretched between the Northern and Southern hemispheres of the outer sphere. These results show that the flow physics in rotating convection is qualitatively different in planar and spherical geometries. This finding underlines that it is crucial to study convection in spherical geometries to better understand geophysical and astrophysical flow phenomena. Key Points We show that in rotating spherical Rayleigh-Benard convection, three regions with distinctly different flow dynamics are formed The mid-latitude region is characterized by convective columns that extend from the Northern to the Southern hemisphere of the outer sphere The diffusion-free scaling indicates that the flow dynamics and heat transport originating in the mid-latitude region are bulk-dominated