Altimeter data for this study was obtained from the NASA Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory/California Institute of Technology. We also thank JPL and G. Kruizinga of the Satellite Geodesy and Geodynamics Group for providing the altimetry database software. S. D. Desai provided the cross-track gradient model. This work was funded by the U.S. National Aeronautics and Space Administration under a Jason science investigation.