Analysis of the Effect of a Mean Velocity Field on Mean Field Dynamo

Abstract: We study semi-analytically and in a consistent manner, the generation of a mean velocity field $\bar{\mathbf{U}}$ by helical MHD turbulence, and the effect that this field can have on a Mean Field Dynamo. Assuming a prescribed, maximally helical small scale velocity field, we show that large scale flows can be generated in MHD turbulent flows, via small scale Lorentz force. These flows back-react on the mean electromotive force of a Mean Field Dynamo through new terms, leaving the original $\alpha $ and $\beta $ terms explicitly unmodified. Cross-helicity plays the key role in interconnecting all the effects. In the minimal $\tau$ closure that we chose to work with, the effects are stronger for large relaxation times.