Kinematic dynamo action in a sphere. I: Effects of differential rotation and meridional circulation on solutions with axial dipole symmetry (Q2713405)

The authors test a two-parameter class of flows for dynamo generation containing an axial dipole. The class of flows includes two completely different types of known dynamos, one dominated by differential rotation \(D\), and one without the differential rotation. It is found that some flows in distinct zones in parameter space act as dynamos, while the remaining flows generate fields that are too small in scale to be resolved by the used numerical methods. The two above-mentioned dynamo types lie in the same zone, ant it is therefore possible to change the flow continuously from one to the other without loosing dynamo action. Differential rotation is found to promote large-scale axisymmetric toroidal magnetic fields, while the meridional circulation \(M\) promotes large-scale axisymmetric poloidal fields concentrated at high latitudes near the axis. Magnetic fields resembling that of the Earth are generated by \(D>0\), corresponding to westward flow at the surface, and by \(M\) of either sign but not zero. Very few oscillatory solutions are found.