CMG Research: Collaborative Research: Models of Sub-Grid Scale Turbulence in Earth's Core and the Geodynamo

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EAR-0222334Paul H. Roberts Earth's dynamo, which is responsible for the geomagnetic field, is a geosystem involving a broad range of interacting scales, a complex geometry and a rich variety of physical processes. Numerical simulations resolve only the largest-scale features; most parameterizations of the smaller, subgrid scale processes simulate dissipative processes only, and are incapable of simulating non-dissipative processes which affect transfers of energy among differing spatial scales. Exceptions to this statement are the recently developed similarity and Navier-Stokes-alpha models. Core dynamics is strongly affected by the action of the Coriolis and Lorentz forces, making the fields both anisotropic and non-local. Recent studies have provided valuable insight into these processes, which will help motivate generalized models that accurately account for these forces. This project will develop better parameterizations of subgrid processes in Earth's core by incorporating into the similarity and Navier-Stokes-alpha models, knowledge of the structure of the small-scale fields. The project will involve a combination of numerical simulation and theoretical analysis employing not only simplified models that isolate physical processes and analytical issues, but also realistic geodynamo models. The research will be undertaken by a group of mathematicians and geoscientists from US institutions and from abroad under the supervision of a management group. The project will foster interactions between members of the dynamo collective, and it is expected that further collaborations will result from the annual workshops that will be organized and partially supported by the project. It is anticipated that improved parameterization of subgrid processes in rotating magnetoconvection will interest all who wish to study magnetism and dynamos in other planets and in stars. It is believed that many of these people will wish to participate in the planned workshops. An improved numerical model of the geodynamo will be of interest to a second group of geoscientists and mathematicians who seek to quantify the structure, dynamics and history of the interior of our planet.--