The dependence of the dynamo alpha on vorticity

Abstract

We use data from numerical simulations of dynamo-generated turbulence in the shearing box approximation to determine the dynamo α-effect and its dependence on the rotation law Ω(r). The data suggest that the dynamo α is not simply proportional to the local angular velocity Ω(r), as is usually assumed, but rather is proportional to the local vorticity ω(r) = r-1 d/dr(Ωr2). We also find tentative evidence to support the proposition that the backreaction of the magnetic field on a sets in when the field reaches equipartition with the energy in the turbulent motions. Furthermore, we propose an explanation as to why the sign of a is found to be opposite to that in the standard picture. © 1997 RAS.