The tachocline and the solar dynamo

The solar tachocline contains a rich variety of physics, and contributes in many ways to the workings of the solar dynamo. It includes complex quasi-equilibrium states supported by the near balances of gas and magnetic pressure gradients, gravity, magnetic curvature stresses, Coriolis and other forces. The dynamics include overshooting convection, waves of several types, hydrodynamic and MHD instabilities on several spatial and temporal scales, several types of boundary layers and dynamo action. The dynamo processes present include the in situ generation of poloidal fields by global MHD and/or magnetic buoyancy instabilities; the advection of these poloidal fields by meridional circulation; the generation of toroidal fields from shearing by the differential rotation; and storage of these fields and their subsequent eruption into the convection zone. The tachocline probably also plays a significant role in creating magnetic patterns that are seen in the photosphere. This talk will of necessity focus on a subset of these topics, including particularly global MHD instabilities and whether we can see evidence of them in surface magnetic data, meridional circulation and the boundary layers that limit it, possible jets in the tachocline, and certain solar dynamo questions.