Parameterization of Small Scale Flow Structures in Earth's Outer Core

Florida State University, Tallahassee FL

Investigators

Abstract

EAR-0000400 Loper, David This is a proposal to model, analyze and parameterize small-scale flows relevant to Earth's core and the geodynamo problem. The research project will consist of three phases, roughly coinciding with the three year duration of the grant. The first phase consists of solving explicitly for the local velocity and magnetic fields generated in a rotating hydromagnetic fluid by a small-scale buoyant parcel of prescribed (Gaussian) shape, including effects of the viscous, Lorentz and inertia forces and ambient stratification. This portion of the project is the most straightforward, although determination of the rise velocity may require solution of a non-linear problem when inertia or stratification is included. In the second phase the solutions obtained during the first phase will be generalized to include the effect of parcel deformation by the fluid flow and the associated temporal evolution of the flow structures. Also, the short-term temporal development of the wake structure associated with a Gaussian parcel, starting from an initial static state, will be analyzed. It is anticipated that this phase will involve a combination of classical analysis and numerical computation. In the third phase the solutions found during the first two phases will be used to quantify (i.e., parameterize) four important nonlinear effects: helicity, electromotive force, Reynolds stress and effective diffusivity. The first two of these are important in the development of more realistic a-w and a2 dynamo models, while the last two should lead to an improvement in the parameterization of small-scale motions in fully 3-D numerical models.