PROPERTIES OF NONLINEAR DYNAMO WAVES

Dynamo theory offers the most promising explanation of the generation of the sun's magnetic cycle. Mean field electrodynamics has provided t he platform for linear and nonlinear models of solar dynamos. However the nonlinearities included are (necessarily) arbitrarily imposed in t hese models. This paper conducts a systematic survey of the role of no nlinearities in the dynamo process, by considering the behaviour of dy namo waves in the nonlinear regime. It is demonstrated that only by co nsidering realistic nonlinearities that are non-local in space and tim e can modulation of the basic dynamo wave be achieved. Moreover this m odulation is greatest when there is a large separation of timescales p rovided by including a low magnetic Prandtl number in the equation for the velocity perturbations.