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E. E. DeLuca (Smithsonian Astrophysical Observatory), N. E. Hurlburt (Lockheed Martin)
The predictions of Mean Field Electrodynamics have been questioned because of the strong feedback of small scale magnetic structure on the velocity fields. In 2-D, this nonlinear feedback results in a lengthening of the turbulent decay time. In 3-D alpha-quenching is predicted. Previous studies assumed a homogeneous fluid. Here we present result of numerical solutions of fully compressible, nonlinear dynamos in two and three dimensions. In two dimensions, we consider an adiabatically stratified layer which experiences a constant shear. A mean-field alpha effect is introduced which is uniform over the layer. This system admits dynamo solutions of both the \alpha-\omega and \alpha2 varieties. This system also experiences a random thermal forcing which generates an additional turbulent diffusion. We seek to understand both the nonlinear actions of this system and the impact of the turbulent motions upon it. The magnetic flux in the convecting region above has a strong influence on the evolution of the dynamo. In three dimensions we model the generation of magnetic field in an adiabatic, stratified layer with random thermal forcing and an imposed velocity shear across the layer. Rather than introduce an artificial alpha effect, we seek a fully self consistent periodic dynamo. We therefore introduce a uniform rotation to the system which, in conjunction with the random forcing produces a mean helicity to the flows. We present the results of these calculations and their implications for the solar cycle.
This work is supported by NASA grant: NAGW-5154
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