Abstract
Geostrophic surface velocity anomalies are used to analyze the annual variations of the large-scale geostrophic currents and of the eddy kinetic energy (EKE) field of the ocean circulation. The underlying geostrophic currents were estimated from the Jason-1-TOPEX/Poseidon (JTP) tandem altimetric sea surface height data using the "parallel track approach'' with a 10 km along-track resolution; however, because of the given separation of the tracks of the two satellites only large mesoscale eddies are resolved by the tandem measurements. The analysis covers the entire 3 year period of the tandem mission (109 repeat cycles) from September 2002 to September 2005. The analysis of the seasonal flow changes reveals annual changes of all major current systems, but especially of the zonal flow field in low latitudes, leading to zonal jets on the annual cycle in the southern Pacific, Atlantic, and Indian oceans. In middle and high latitudes, indications of a seasonally modulated strength of the Sverdrup circulation emerge from the analysis. The EKE field also shows changes in its amplitude on the annual period. In low latitudes, those can be rationalized as resulting from seasonally modulated currents. In middle and high latitudes, changes in the wind-driven barotropic circulation loom large, which are not represented in other altimetric velocity products. Results shown suggest that velocity time series of the JTP tandem mission should be continued through similar constellations, e. g., of Jason-1 and Jason-2.
