Velocity Statistics Inferred from the TOPEX/Poseidon-Jason-1 Tandem Mission Data

Abstract

Using a parallel-track approach to estimate geostrophic surface velocities, an estimate of the statistics of ocean geostrophic surface currents and momentum stresses is provided on a 10 km along-track resolution from the first 49 repeat cycles (16 months) of the Jason-TOPEX/Poseidon tandem altimetric sea surface height (SSH) data. Results are compared with estimates obtained in a traditional way from along-track SSH data at crossover points and with in situ, Acoustic Doppler Current Profiler (ADCP) measurements obtained on board the VOS Oleander along a nominal path connecting Bermuda with the U.S. mainland. Agreements with the Oleander data are reasonable when simultaneous (in space and time) sampling is available. However, amplitudes of parallel-track geostrophic velocity variances are about 25% lower as compared to Oleander measurements which represent geostrophic and ageostrophic flow components. Estimates of velocity variances show clear signs of an anisotropic eddy field in the vicinity of all major current systems. At the same time estimates of Reynolds stresses and eddy momentum fluxes show a convergence of eddy momentum in all those regions, suggesting a forcing of the mean flow by the eddy field there.

Keywords:

• altimetry
• mesoscale eddies
• ocean circulation

Acknowledgments

We are grateful to Sandra Fontana and Tom Rossby for providing the VOS Oleander ADCP velocities and Chelle Gentemann from Remote Sensing Systems for providing the microwave SST analysis. We thank Olwijn Leeuwenburgh for help and valuable suggestions. Charmaine King helped with the processing of the T/P and Jason-1 altimeter data. Victor Zlotnicky provided the PO-DAAC version of the corrected T/P data that were adjusted to new Jason-1 environmental corrections. Altimeter data sets were received from the NASA PO-DAAC data center. Supported in part through ONR (NOPP) ECCO grants N00014-99-1-1049, through NASA grant NAG5-7857, and through a contract with the Jet Propulsion Laboratory (1205624). Partial support through the Deutsche Forschungs Gemeinschaft (SFB 512, Teilprojekt E1) is acknowledged. We thank two anonymous referees for valuable comments. This is a contribution of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO) funded by the National Oceanographic Partnership Program.