Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and-2

This study focuses on the improved estimation of mesoscale surface ocean ci rculation obtained by merging TOPEX/Poseidon (T/P) and ERS-1 and -2 altimet er measurements between October 1992 and May 1998. Once carefully intercali brated and homogenized, these data are merged through an advanced global ob jective analysis method that allows us to correct for residual long wavelen gth errors and uses realistic correlation scales of ocean dynamics, The hig h-resolution (0.25 degrees x 0.25 degrees) merged T/P + ERS-1 and -2 sea le vel anomaly maps provide more homogeneous and reduced mapping errors than e ither individual data set and more realistic sea level and geostrophic velo city statistics than T/P data alone. Furthermore, the merged T/P + ERS-1 an d -2 maps yield eddy kinetic energy (EKE) levels 30% higher than maps of T/ P alone. They also permit realistic global estimates of east and north comp onents of EKE and their seasonal variations, to study EKE sources better. A comparison of velocity statistics with World Ocean Circulation Experiment surface drifters in the North Atlantic shows very good agreement. Compariso n with contemporary current meter data in various oceanic regimes also prod uces comparable levels of energy and similar ratios of northward and eastwa rd energy, showing that the maps are suitable to studying anisotropy. The T /P + ERS zonal and meridional components of the mapped currents usually pre sent comparable rms variability, even though the variability in the Atlanti c is more isotropic than that in the Pacific, which exhibits strong zonal c hanges. The EKE map presents a very detailed description, presumably never before achieved at a global scale. Pronounced seasonal changes of the EKE a re found in many regions, notably the northeastern Pacific, the northeaster n and northwestern Atlantic, the tropical oceans, and the zonally extended bands centered near 20 degrees S in the Indian and western Pacific Oceans a nd at 20 degrees N in the northwestern nl Pacific.