Cross-helicity dynamo and flow generation

by Dr Nobumitsu Yokoi (Institute of Industrial Science, University of Tokyo)

Thursday 11 Oct 2012, 13:30 → 14:30 Europe/Stockholm

(Nordita) (122:026)

First the cross-helicity effect is explained in the context of dynamos. In the presence of the mean vortical motion, the cross-correlation between the velocity and magnetic fluctuations (turbulent cross helicity) contributes to the turbulent electromotive force parallel to the mean vorticity. This effect is expected to play an important role in suppression of turbulent magnetic diffusivity. One of the features of the cross-helicity dynamo is alignment of the mean electric current and the mean vorticity, which generally allows a finite mean Lorentz force. This is in strong contrast with the alpha dynamo, where the mean Lorentz force vanishes. At the same time, the cross-helicity effect appears in the Reynolds (and turbulent Maxwell) stresses. Coupled with the mean magnetic strain, the turbulent cross helicity may contribute to the suppression of turbulent or eddy viscosity. Several features of the cross-helicity effects in dynamos are summarized. Finally, recent developments in the study of the cross-helicity effects in the context of the magnetic reconnections are discussed.