Dynamo efficiency in compressible convective dynamos with and without penetration

Abstract

We investigate dynamo action in compressible convection via numerical simulations in a Cartesian domain. We directly compare the dynamo properties of a fully convective domain with the same domain extended to include an underlying stable region. These simulations extend models of fully convective domains with open lower boundary conditions to a more self-consistent model. We examine whether the extremely slow recirculation of the lower region affects the dynamo properties in the convection zone. We find that the dynamo properties of the upper convective region are essentially unchanged by the addition of the lower stable region. After a transient period, dynamo action in the convective region not only proceeds as normal, but also extends into the region of overshooting flow in the stable region. Downward magnetic pumping, long recirculation times and the low percentage of rising elements that transit the vertical extent of the domain all fail to eliminate the dynamo. Sufficient magnetic field is recirculated or remains in the convective region to fuel the local dynamo there. The independence of the convective layer from the conditions of the lower layer makes the dynamo truly local.

Keywords:

• Magnetohydrodynamics
• Dynamos
• Convection

Acknowledgements

The authors would like to thank the organisers of the Natural Dynamos conference in Stara Lesna, Slovakia, 2009, the organisers of the Kavli Institute for Theoretical Physics program on Dynamo Theory in Santa Barbara, 2008, and acknowledge the support from NASA grant NNX07AL74G and from NSF Teragrid supercomputing resources under grant TG-MCA08X016.