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Tuesday 20 Jun 2017Convection driven dynamos with self-consistent shear

Laura Currie - University of Exeter

4th Floor Interaction Area 11:15-11:45

It is widely accepted that astrophysical magnetic fields are generated by dynamo action. In many cases these fields exhibit organisation on a scale larger than that of the underlying turbulent flow (e.g., the eleven-year solar cycle). The mechanism for the generation of so-called large scale fields remains an open problem. In cases where the magnetic Reynolds number (Rm) is small, dynamo-generated fields are coherent but at (the astrophysically relevant) high Rm, the fields are overwhelmed by small scale fluctuating field. Recently Cattaneo \& Tobias (2014) have shown that an imposed large scale shear flow can suppress the small scale fluctuations and allow the large scale temporal behaviour to emerge. However, in these previous models at high Rm the shear is often artificially imposed or driven by an arbitrary body force. Here we consider a simple kinematic model of a convective dynamo in which shear is self consistently driven by the presence of a horizontal temperature gradient (resulting in a thermal wind) and a rotation vector that is oblique to gravity. By considering a 2.5 dimensional system, we are able to reach high Rm so that the dynamo is in the asymptotic regime where the growth rate becomes independent of Rm. We examine the role the shear has in modifying the dynamo at high Rm.

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