Thermal Winds in the Tangent Cylinder

Details Thermal Winds in the Tangent Cylinder Thermal Winds in the Tangent Cylinder

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmgp44a..08a&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #GP44A-08

Physics

Fluid Dynamics

1213 Earth'S Interior: Dynamics (1507, 7207, 7208, 8115, 8120), 1507 Core Processes (1213, 8115), 1510 Dynamo: Theories And Simulations, 1560 Time Variations: Secular And Longer, 5440 Magnetic Fields And Magnetism

Scientific paper

Thermal winds inside the tangent cylinder naturally develop in models of core fluid dynamics and can explain a broad array of deep Earth observations. The tangent cylinder, the imaginary axial cylinder that circumscribes the inner core equator, acts to separate the outer core into three distinct regions: outside the tangent cylinder and inside the tangent cylinder in the northern and southern hemispheres. Here we present the results of laboratory convection experiments and numerical dynamo models that demonstrate that thermal winds dominate the large-scale flow inside the tangent cylinder. These thermal winds are azimuthal zonal flows that are retrograde (westward) just below the core-mantle boundary and prograde (eastward) just above the inner core boundary. In both laboratory and numerical studies, the typical zonal velocity within the tangent cylinder, U, follows an asymptotic thermal wind scaling law: U ~ (B/Ω)1/2, where B is the buoyancy flux in the Earth's core and Ω is the planetary angular velocity. Further support for tangent cylinder thermal winds comes from frozen flux models of flow below the core-mantle boundary. In these models, strong retrograde zonal flows exist at high latitudes and then drop off sharply at lower latitudes outside the tangent cylinder. In addition, we present models of inner core super-rotation based on electromagnetic coupling of prograde thermal wind flows at the inner core boundary. Together these forward and inverse models suggest that thermal winds inside the tangent cylinder are an integral component of the large-scale dynamics of the Earth's core.

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