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Towards Planetary “BRAIN SCANS” – An Eddy Permitting Global Ocean & Sea-Ice Model on a Quasi-Uniform Expanded Cube Grid Suitable for Decadal Time-scale Data Assimilation

Chris Hill
Department of Earth, Atmospheric, and Planetary Sciences
MIT
December 10, 2004
 
This talk will describe preliminary results from an eddy permitting ocean and sea-ice configuration of the M.I.T. General Circulation Model (MITgcm – see http://mitgcm.org) that is designed to support dynamically reasonable estimates of the full three-dimensional, time-varying oceanic state on decadal time-scales. Undertaken as part of the Estimating the Circulation and Climate of the Ocean (ECCO – see http://www.ecco-group.org) project, the model configuration presented is suited to constraints by both remotely-sensed (altimeter, scatterometer, ocean temperature, ice cover and gravity) data and by in-situ (temperature and salinity profilers, mooring, drifter and float) data using advanced, mathematically rigorous, assimilation methods (adjoint method, Kalman filter and Rauch-Tung-Striebel smoother).
 

Our model configuration employs a novel gridding approach that avoids singularities anywhere on the sphere by projecting grid-lines from an embedded cube onto the sphere surface. Using this approach we obtain a truly global grid with no singularities anywhere on the sphere. The grid has maximal grid spacing of 25.9 km and minimal grid spacing of 3 km. The global coverage of the grid allows us to include an interactive representation of the polar oceans and of sea-ice into our assimilation system. The grid spacing is sufficient to allow a rich mesoscale eddy field to emerge. Using state-of-the-art large-scale parallel computer resources, committed to the project by NASA, the system simulates several years in a day. This throughput is sufficient to allow a practical, semi-continuous assimilation system that partially resolves the ocean eddy field to be envisaged. In this presentation we will describe steps taken so far to achieve an optimal system configuration for this work and towards our goal of performing a planetary scale “brain-scan” that will globally map the full three-dimensional time dependent state of the ocean and sea-ice system at high resolution over the last ten to thirty years.
 
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