Dynamo Action in the Solar Convection Zone and Tachocline: Pumping and Organization of Toroidal Fields

We present the first results from three-dimensional spherical shellsimulations of magnetic dynamo action realized by turbulent convectionpenetrating downward into a tachocline of rotational shear. This permits us toassess several dynamical elements believed to be crucial to the operation ofthe solar global dynamo, variously involving differential rotation resultingfrom convection, magnetic pumping, and amplification of fields by stretchingwithin the tachocline. The simulations reveal that strong axisymmetric toroidalmagnetic fields (about 3000 G in strength) are realized within the lower stablelayer, unlike in the convection zone where fluctuating fields are predominant.The toroidal fields in the stable layer possess a striking persistentantisymmetric parity, with fields in the northern hemisphere largely ofopposite polarity to those in the southern hemisphere. The associated meanpoloidal magnetic fields there have a clear dipolar geometry, but we have notyet observed any distinctive reversals or latitudinal propagation. The presenceof these deep magnetic fields appears to stabilize the sense of mean fieldsproduced by vigorous dynamo action in the bulk of the convection zone.Comment: 4 pages, 3 color figures (compressed), in press at ApJ