Combining altimeter and subsurface float data to estimate the time-averaged circulation in the upper ocean

A new technique is presented for estimating time-averaged, upper ocean geostrophic velocity from a combination of altimeter data and subsurface float data. The technique makes uses of the strong relationship between sea-surface height anomaly and anomalous velocity at depth to reduce mesoscale eddy variability in subsurface float displacements. The technique is demonstrated on a region in the North Atlantic that was well sampled by Argo floats. The 2004 through 2006 time-averaged density field was estimated from the surface to 2000 db by combining altimeter and hydrographic data from the floats. In addition, a reference velocity field was estimated at 1000 db based on a combination of altimeter data and subsurface float displacements. The reference velocity field was combined with geostrophic shear based on the density field to produce a three-dimensional estimate of geostrophic velocity from the surface to 2000 db. The Gulf Stream transport in the upper 2000 db is estimated to be 76 Sv at 73 degrees W. In addition, an estimate of the 3-year average dynamic height at the surface was computed by combining the 1000-db reference dynamic height and the time-averaged density field.