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Mean surface circulation of the global ocean inferred from satellite altimeter and drifter data

Nikolai Maximenko(1) and Peter Niiler(2)

(1) IPRC/SOEST, University of Hawaii, 1680 East West Road, POST #401, Honolulu, Hawaii 96822, United States
(2) Scripps Institution of Oceanography, UCSD, 8851 Shellback Way, Keck-OAR Vedelstein Bldg. #160, La Jolla, California 92093-0213, United States

Abstract

A simplified form of horizontal momentum equation containing full acceleration, Coriolis force, pressure gradient and Ekman stress terms is used to combine data of the Aviso merged sea level anomaly, global array of near-surface drifters and NCEP reanalysis winds demonstrating good agreement with each other at high spatiotemporal resolution. Thus utilized drifter velocities provide the missing reference to satellite altimeter observations who in their turn correct the bias due to inhomogeneous distribution of Lagrangian drifters. Acceleration is shown to be an important part of cyclostrophic balance in the regions of high eddy energy.

Study of the relation between Ekman currents at the drifter drogue depth (15m) and local wind revealed significant variations both in latitude and longitude, strong seasonality and non-linearity to the wind speed. These variations are in a qualitative agreement with the theoretical effect of intensity of vertical mixing in the ocean mixed layer and stability of the atmospheric boundary layer and are used to improve the parameterizations of Ekman stress and velocity to NCEP reanalysis wind at 10 m level.

Local estimates of horizontal pressure gradient are combined with the data of the Gravity Recovery And Climate Experiment (GRACE) and integrated to produce the global grid of the 1992-2004 mean dynamic ocean topography (DOT) at mesoscale resolution. Mean geostrophic velocities derived from this DOT are used to revise the patterns of surface circulation in various regions. They reveal remarkable fine structure of major large-scale flows, such as the Gulf Stream, Kuroshio Extension and Antarctic Circumpolar Current. They also suggest corrections to the previous description of the South Atlantic Current with the change of its role from a branch of the Brazil Current to a southern analogue of the Azores Current and detect a system of relatively weak steady nearly zonal jets in the eastern North and South Pacific.

 

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                 Last modified: 07.10.03