Collaborative Research for WOCE-AIMS: Global Velocity Estimation Project

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

0137122/0137077 Owens/McWilliams This collaborative project will try to estimate the large scale, three-dimensional velocity field for the North Atlantic using velocity data from sub-surface floats, current meters, and surface drifters, hydrographic profiles, and sea surface height measurements taken prior to and during the field operations phase of the World Ocean Circulation Experiment (WOCE). As new measurements, such as the gravimetry from the GRACE mission, altimetry from the JASON mission, and velocities and T and S profiles from the ARGO float program become available, they will be incorporated into the analysis. The estimates of the velocities and their expected errors will be made using generalized least-square error minimization based on a priori specification of expected measurement errors and space-time covariances and/or basis functions. A hierarchy of a priori statistics will be used. They will be determined from general spectral shapes for stretched basin basis functions and analyses of simulations from numerical general circulation models run for other purposes, as well as statistical analyses from the measurements. The model covariances and basis functions initially will exactly enforce geostrophic dynamics, with additional ageostrophic processes added where necessary, such as in the surface boundary layer and near the Equator. The use of slightly less constrained covariances calculated directly from the simulations will also be examined. The a posteriori statistics of the estimates will be compared with the a priori ones to evaluate the estimation procedure and the validity of the models. A sequence of estimations with expanding comprehensiveness will be made. Initially these estimates will be obtained for the mean circulation in highly sampled regions, i.e., the Atlantic Climate and Circulation Experiment and then expanded to first basin then global maps. As we gain confidence in the procedure, maps for temporally varying velocities will also be made. The ultimate goal is to create a living estimation library and software system, capable of user-chosen variants and re-estimation with new data. This project is a contribution to WOCE