Validation of the geostrophic method for estimating zonal currents at the equator from Geosat altimeter data

The applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meridionally differenced form of the geostrophic balance. Estimates of geostrophic zonal flow anomalies in the equatorial Pacific have been deduced from 17-day collinear altimeter data during the first year of the Geosat Exact Repeat Mission, November 1986 to November 1987. Altimeter-derived geostrophic estimates agree well with in situ zonal current variability. Sea level and zonal velocity solutions from a tropical Pacific numerical model were used as proxy data sets in order to estimate errors induced into the geostrophic calculation by the Geosat space-time sampling. -from Authors