We have developed a new technique for extracting global mesoscale variability from satellite altimeter profiles having large radial orbit error (-3 m). Long-wavelength radial orbit error, as well as other longwavelength errors (e.g., tides, ionospheric-atmospheric delay, and electromagnetic bias), are suppressed by taking the derivative (slope) of each altimeter profile. A low-pass filter is used to suppress the shortwavelength altimeter noise (• < 100 km). Twenty-two repeat slope profiles are then averaged to produce a mean sea surface slope profile having a precision of about 0.1 grad. Variations in sea surface slope, which are proportional to changes in current velocity, are obtained by differencing individual profiles from the average profile. Slopes due to mesoscale dynamic topography are typically 1 grad (i.e., a 0.1-m change in topography over a 100-km distance). Root-mean-square (rms) slope variability as low as 0.2 grad are found in the southeast Pacific, and maximum slope variations up to 6-8 grad are found in major westem boundary currents (e.g., Gulf Stream, Kuroshio, Falkland, and Agulhas) and Antarctic Circum-polar Current (ACC) systems. The global rms variability map shows previously unknown spatial details that are highly correlated with seafloor topography. Over most areas, the rms slope variability is less than 1 grad. However at mid-latitudes, areas of higher variability occur in deep water (> 3 km) adjacent to continental shelves, spreading ridges, and oceanic plateaus. Variability is low in shallower areas (< 3 km). Along the ACC, the meso-scale variability appears to be organized by the many shallow areas in its path. We do not see convincing evidence that variability is higher downstream from topographic protrusions. Instead, the areas of highest variability occur in the deep basins (> 4 km). 1Now at Geologic Research Division, Scripps Institution of Oceanogra-mesoscale variability of the oceans that are generally consistent phy, La Jolla, California. with historical data [Wyrtki et al., 1976]. One of the surprising results from the analysis of Seasat data was that over most ocean Copyright 1989 by the American Geophysical Union. areas the mesoscale variability is quite low (< 40 mm). The small-Paper number 89JCO1397. er areas of high variability are associated with western boundary 0148-0227/89/89JC-01397505.00 currents and the Antarctic Circumpolar Current. 17,971 17,972 SANDWELL AND ZHANG: GLOBAL MESOSCALE VARIABILITY