TOWARD A MEAN FIELD FORMULATION OF THE BABCOCK-LEIGHTON TYPE SOLAR DYNAMO. I. a-COEFFICIENT VERSUS DURNEYÏS DOUBLE-RING APPROACH

We develop a model of the solar dynamo in which, on the one hand, we follow the Babcock-Leighton approach to include surface processes, such as the production of poloidal Ðeld from the decay of active regions, and, on the other hand, we attempt to develop a mean Ðeld theory that can be studied in quantitative detail. One of the main challenges in developing such models is to treat the buoyant rise of the toroidal Ðeld and the production of poloidal Ðeld from it near the surface. A previous paper by Choudhuri, & Dikpati in 1995 did not incorporate buoyancy. We extend this model by two contrastSchuŽ ssler, ing methods. In one method, we incorporate the generation of the poloidal Ðeld near the solar surface by DurneyÏs procedure of double-ring eruption. In the second method, the poloidal Ðeld generation is treated by a positive a-e†ect concentrated near the solar surface coupled with an algorithm for handling buoyancy. The two methods are found to give qualitatively similar results. Subject headings : MHD È Sun: interior È Sun: magnetic Ðelds