AXISYMMETRICAL MEAN-FIELD DYNAMOS WITH DYNAMIC AND ALGEBRAIC ALPHA-QUENCHINGS

We study axisymmetric mean field spherical and spherical shell dynamo models, with both dynamic and algebraic alpha-quenchings. Our results show that there are qualitative as well as quantitative differences an d similarities between these models. Regarding similarities, both grou ps of models exhibit symmetric, antisymmetric and mixed modes of behav iour. As regards differences, the important feature in the full sphere models is the occurrence of chaotic behaviour in the algebraic alpha- quenching models. For the spherical shell models with dynamic alpha th e main features include the possibility of multi-attractor regimes wit h final state sensitivity with respect to small changes in the magnitu de of alpha and the initial parity. We find the effect of introducing a dynamic alpha is likely to be complicated and depend on the region o f the parameter space considered, rather than a uniform change towards simplicity or complexity.