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 ^ { -1 } , 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 .