The latitude belts of solar activity as a consequence of a boundary-layer dynamo

Abstract

HELIOSEISMOLOGY has provided much insight into the Sun's activity, allowing measurements of the thickness of the solar convection zone and the internal solar rotation rate as a function of latitude and depth. Solar activity is generally thought to result from dynamo action within the Sun, but there has been some debate as to whether this action occurs in the whole convection zone, at the base of the convection zone, or in the boundary layer between the convection and radiative zones^1,2 (about 0.65 R_⊙ to 0.7 R_⊙). Here we point out that recent helioseismological data^3–7 seem consistent with the last location. We present the results of calculations on a model in which dynamo action arises in a very thin (0.05 R_⊙) spherical boundary layer, which are consistent with the observations. In particular, this model provides an explanation of why there exists a latitudinal boundary on the solar surface, below which features such as sunspots migrate towards the equator whereas above it they migrate polewards.