A dynamo model for axisymmetric and non-axisymmetric solar magnetic fields

Increasing observations are becoming available about a relatively weak, but persistent, non-axisymmetric magnetic field co-existing with the dominant axisymmetric field on the Sun. It indicates that the non-axisymmetric magnetic field plays an important role in the origin of solar activity. A linear non-axisymmetric α − Ω dynamo model is set up to discuss the characteristics of the axisymmetric (m = 0) and the first nonaxisymmetric (m = 1) modes and to provide further the theoretical bases to explain the ‘active longitude’, ‘flip-flop’ and other non-axisymmetric phenomena. The model consists of a updated solar internal differential rotation, a turbulent diffusivity varied with depth and an α-effect working at the tachocline in rotating spherical systems. The difference between the α −Ω and the α− Ω models and the conditions to favor the non-axisymmetric modes with the solar-like parameters are also presented.