Variations of global mesoscale eddy energy observed from Geosat

Abstract

The global distribution of eddy kinetic energy has been synoptically observed from analysis of the Geosat Exact Repeat Mission (ERM) altimeter data collected for a 2‐year period from November 1986 through November 1988. Using a technique developed by Sandwell and Zhang (1989), altimeter data from forty‐four 17‐day repeat cycles (2 years) were processed into sea surface slopes along the satellite ground track, averaged, and filtered to produce a mean sea surface slope profile having an estimated accuracy of 0.2 μrad (2 cm sea level change over 100 km distance). A series of global eddy kinetic energy maps, each averaged over 3 months, and their mean were then generated. The maximum mean eddy kinetic energy per unit mass exceeds 2000 cm2/s2 for most of the western boundary currents; however, it only reaches approximately 500 cm2/s2 for the Antarctic Circumpolar Current (ACC). More than 65% of the world ocean has relatively low variability with an eddy kinetic energy of less than 300 cm2/s2. Results obtained from this study are in general agreement with other Geosat ocean variability studies (e.g., Zlotnicki et al., 1989). However, significantly higher variability is found when compared with either Seasat or ship drift data. Significant seasonal variations were found in the Gulf Stream and Kuroshio currents. The ACC system exhibits no apparent seasonal variation.