Dynamo efficiency with shear in helical turbulence

Abstract

To elucidate the influence of shear flow on the generation of magnetic fields through the modification of turbulence property, we consider the case where a large-scale magnetic field is parallel to a large-scale shear flow without direct interaction between the two in the kinematic limit where the magnetic field does not backreact on the velocity. By nonperturbatively incorporating the effect of shear in a helically forced turbulence, we show that turbulence intensity and turbulent transport coefficients (turbulent viscosity, α and β effect) are enhanced by a weak shear, while strongly suppressed for strong shear. In particular, β is shown to be much more strongly suppressed than α effect. We discuss its important implications for dynamo efficiency, i.e., on the scaling of the dynamo number with differential rotation. © 2009. The American Astronomical Society. All rights reserved.