Heat transfer and thermal mixing in planetary dynamo models

Details Heat transfer and thermal mixing in planetary dynamo models Heat transfer and thermal mixing in planetary dynamo models

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31c1259k&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P31C-1259

Physics

Geophysics

[1507] Geomagnetism And Paleomagnetism / Core Processes, [1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [4490] Nonlinear Geophysics / Turbulence, [5430] Planetary Sciences: Solid Surface Planets / Interiors

Scientific paper

The magnetic fields of planets and stars are generated by the motions of electrically conducting fluids within them. These fluid motions are likely driven by convection, and that convection is subject to the effect of the bodies' rotation. Under the strong influence of rotation, convective flow is organized by the Coriolis force into quasigeostrophic, axially aligned structures. This organization inhibits heat transfer and thermal mixing by imposing effective stratification on convective flows. Planets and stars, however, are turbulent bodies, and are typically expected to be well-mixed. Thus, despite low Rossby numbers (Ro<<1), many bodies are thought to be homogenized by strong turbulence on account of their high Reynolds numbers (Re>>1). This apparent paradox also obscures the application of heat transfer scaling laws to these bodies. We report an investigation of the influence of rotation on convective heat transfer and thermal mixing via a broad set of numerical dynamo models (5e-7 < E < 5e-4; 3e5 < Ra < 2e9; 0.1 < Pr < 30; 0.06 < Pm < 20; 10 < Re < 3e3). We find two distinct regimes: a rapidly rotating regime in which the influence of rotation is dominant; and a weakly rotating regime in which the importance of rotation is secondary. The transition between regimes is linked to the thicknesses of the thermal and viscous boundary layers. Heat transfer scaling laws are identified for each regime. Furthermore, thermal mixing is also shown to depend on the boundary layer nesting, and is not strongly dependent on the Reynolds number. Identification of the regime boundary in terms of the Rayleigh (Ra) and Ekman (E) numbers allows the extrapolation of appropriate heat transfer scalings and effective thermal mixing to planets and stars.

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