ON THE POSSIBILITY OF AN ALPHA-2-OMEGA-TYPE DYNAMO IN A THIN-LAYER INSIDE THE SUN

If the solar dynamo operates in a thin layer of 104 km thickness at the interface between the convection zone and the radiative core, using the facts that the dynamo should have a period of 22 years and a half-wavelength of 40° in the θ-direction, it is possible to impose restrictions on the values which various dynamo parameters are allowed to have. We point out that the dynamo should be of α2ω nature, and we present kinematical calculations for free dynamo waves and for dynamos in thin rectangular slabs with appropriate boundary conditions. An α2ω dynamo is expected to produce a significant poloidal field which does not leak to the solar surface. We find that the turbulent diffusity η and α-coefficient are restricted to values within about a factor of 10, the median values being η∼ 1010 cm2 s-1 and α ∼ 10 cm s-1. On the basis of mixing length theory, we point out that such values imply a reasonable turbulent velocity of the order 30 m s-1, but rather small turbulent length scales like 300 km.