THE EVOLUTION OF THE SUNS POLOIDAL FIELD

We present here a model to explain how the weak large-scale diffuse ma gnetic fields of the Sun migrate poleward in contrast to the sunspots which migrate equatorward with the progress of the solar cycle. We stu dy the evolution of the Sun's poloidal field in the convection zone by assuming that it is produced by an equatorward-propagating dynamo wav e at the base of the convection zone and is then subject to turbulent diffusion and a meridional circulation with a poleward surface flow. T he magnetic fieldlines in the lower part of the convection zone first move towards the equator where they are pushed upward by the upwelling meridional flow there to form magnetic bubbles by joining with their opposite hemisphere counterparts. After reaching the surface, these bu bbles drift to higher latitudes with the poleward meridional flow. Our model incorporates the three-dimensional vector character of the magn etic field, whereas the previous flux transport models treated the mag netic field as a scalar on the two-dimensional solar surface.