Comparison of the SGS models for dynamo simulations in rotating spherical shell and plane layer model

Details Comparison of the SGS models for dynamo simulations in rotating spherical shell and plane layer model Comparison of the SGS models for dynamo simulations in rotating spherical shell and plane layer model

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31c1261m&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P31C-1261

Physics

[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations

Scientific paper

Flow and magnetic field in the outer core are distributed over a vast range of length scale from the size of the outer core to the thickness of the boundary layers. Numerical simulations cannot include the full range of scales, so sub-grid scale (SGS) models are required to account for the effects of the unresolved fields on the large scale fields in geodynamo simulations. We performed a large-eddy simulation (LES) of a dynamo in a rotating spherical shell and a rotating plane layer model using the dynamic scale-similarity SGS model. We use the same SGS model for both simulations, but we find some important differences in the behaviors of the SGS terms between these simulations. In the present study, we compare the characteristics of the SGS terms in these geometries. The SGS model employed in the simulations is a dynamic scale-similarity model. We include terms for the SGS momentum and heat flux, the SGS Lorentz force, and the SGS magnetic induction. We also correct the commutation error caused by interchanging the order of the spatial differentiations and filtering operation. The amplitudes of the SGS term and commutation error correction are adjusted automatically with a dynamic scheme, based on the Germano identity. Spatial averaging is required in the dynamic scheme to obtain reliable model coefficients. We average over longitude in the spherical shell model and over horizontal surfaces in the plane layer model. In the simulation results, the energy flux in the magnetic induction term exhibits the largest difference between the simulations in the two domains. In the rotating plane layer model, energy flux of the SGS induction term is negative at all vertical positions z. The energy flux of the SGS induction term in the spherical shell model is also negative near the inner boundary but becomes positive near the outer boundary.

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