AN AZIMUTHAL DYNAMO WAVE IN SPHERICAL SHELL CONVECTION

Abstract

We report the finding of an azimuthal dynamo wave of a low-order (m=1) mode\nin direct numerical simulations (DNS) of turbulent convection in spherical\nshells. Such waves are predicted by mean field dynamo theory and have been\nobtained previously in mean-field models. Observational results both from\nphotometry and Doppler imaging have revealed persistent drifts of spots for\nseveral rapidly rotating stars, but, although an azimuthal dynamo wave has been\nproposed as a possible mechanism responsible for this behavior, it has been\njudged as unlikely, as practical evidence for such waves from DNS has been\nlacking. The large-scale magnetic field in our DNS, which is due to\nself-consistent dynamo action, is dominated by a retrograde m=1 mode. Its\npattern speed is nearly independent of latitude and does not reflect the speed\nof the differential rotation at any depth. The extrema of magnetic m=1\nstructures coincide reasonably with the maxima of m=2 structures of the\ntemperature. These results provide direct support for the observed drifts being\ndue to an azimuthal dynamo wave.\n