Seasonal variations of the large-scale geostrophic flow field and eddykinetic energy inferred from the TOPEX/Poseidon and Jason-1tandem mission data

摘要

Geostrophic surface velocity anomalies are used to analyze the annual variationsof the large-scale geostrophic currents and of the eddy kinetic energy (EKE) field ofthe ocean circulation. The underlying geostrophic currents were estimated from theJason-1 -TOPEX/Poseidon (JTP) tandem altimetric sea surface height data using the"parallel track approach" with a 10 km along-track resolution; however, because ofthe given separation of the tracks of the two satellites only large mesoscale eddies areresolved by the tandem measurements. The analysis covers the entire 3 year period of thetandem mission (109 repeat cycles) from September 2002 to September 2005. Theanalysis 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 annualcycle 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 theanalysis. The EKE field also shows changes in its amplitude on the annual period. In lowlatitudes, those can be rationalized as resulting from seasonally modulated currents. Inmiddle and high latitudes, changes in the wind-driven barotropic circulation loom large,which are not represented in other altimetric velocity products. Results shown suggest thatvelocity time series of the JTP tandem mission should be continued through similarconstellations, e.g., of Jason-1 and Jason-2.