We will use altimeter data in conjunction with data from the Gravity Recovery and Climate Experiment (GRACE) satellite, surface and subsurface drifters, and hydrographic data from the Argo array to estimate the time-averaged, three dimensional velocity in the upper ocean and sea surface height relative to the geoid. All of these ocean observing systems provide complementary information about circulation in the upper ocean, but no standardized analysis product using all of these data exists.
In this analysis, three dimensional maps of upper ocean velocity are produced using an extended optimal interpolation (OI) formalism that includes weak constraints and other data beyond geostrophic velocity and dynamic pressure. As additional data become available, for example Argo float velocity and profile data, they are incorporated into the analysis. Pre-Argo float data is used in conjunction with altimeter and drifter data to estimate decadal changes in ocean circulation over the past 10 years. The circulation maps that result from this work are examined to understand the general circulation of the ocean.
This work provides the oceanographic community with a standard analysis product for velocity similar to the temperature and salinity analyses that have found widespread utility. The product will also provide a metric against which circulation from numerical ocean models can be measured. As models are used throughout the oceanographic community for process studies, data assimilation, real-time forecasting, and climate change simulations, it is critically important to have a benchmark with which to measure their fidelity. In particular, output from the Estimating the Circulation and Climate of the Ocean (ECCO) data assimilation models will be compared with maps of upper ocean velocity. This will provide valuable feedback to the ECCO project by allowing critical evaluation of the model against a purely observational analysis of upper ocean circulation.
Global Upper Ocean Velocity