On Solar Radius Variation with Magnetic Field

In response to the claim by Dziembowski et al. (2001) that the solar radius decreases with magnetic activity at the rate of 1.5 km/yr, we consider the theoretical question whether a radius variation is expected with the solar cycle. If the radius variation is caused by the magnetic pressure of toroidal flux tubes at the bottom of the convection zone, then the dynamo model of Nandy and Choudhuri (2002) would suggest a radius decrease with magnetic activity, in contrast to other dynamo models which would suggest a radius increase. However, the radius decrease is estimated to be only of the order of hundreds of metres.