The importance of physical structure in solar dynamo models

Abstract

We investigate numerically a simplified, interface-type dynamo model with two spatial dimensions, using Cartesian geometry, by examining the effect of various plausible modifications in the physics and geometry in order to approximate conditions in the solar convection zone and overshoot layer. We describe such modifications as changes to the structure of the model. We are particularly interested in the effects of such structural changes on models which incorporate the nonlinear feedback between the magnetic field and the rotational profile via the Malkus-Proctor feedback mechanism, since this form of nonlinearity can reproduce important phenomena such as torsional oscillations and grand minima. We also examine recent claims that, with such a nonlinearity, there exists generic behaviour which is robust to changes in the structure of the model. We find that there is no generic sequence of behaviour for these interface models, but rather that altering physical details of the model can produce major changes in observable signatures, from the very start of the bifurcation sequences. A significant overall result is that the configuration of the migrating field belts can be strongly dependent on depth. Thus, the question of the exact regions in which solar activity tracers (e.g. sunspots) are formed becomes important for comparison of dynamo theory with solar observations.