DIFFUSIVITY QUENCHING AS A MECHANISM FOR PARKERS SURFACE DYNAMO

This paper discusses how the quenching of the magnetic diffusivity by a magnetic field can lead self-consistently to a realistic scenario fb r dynamo action at the base of the solar convection zone. An alpha ome ga dynamo model is developed to test Parker's hypothesis that quenchin g the diffusivity inversely with the magnetic energy in a nonlinear dy namo model leads to the restriction of the field to a thin layer at an interface between a layer of shear (omega-effect) and cyclonic turbul ence (alpha-effect). As the dynamo number is increased, solutions jump discontinuously roma branch of ''weak-field'' solutions to another wh ere strong magnetic field is generated in a layer of reduced diffusivi ty. Hysteresis between these: two solutions is observed, and this is t hen explained by deriving a simpler model using physical arguments. Th is model predicts the occurrence of a cusp catastrophe which may be fo und In the partial differential equations. The results are relevant to a solar dynamo acting at the base of the convection zone and may give an insight into the mechanism leading to the appearance of grand mini ma in solar activity.