STATISTICS OF GEOSTROPHIC TURBULENCE IN THE SOUTHERN-OCEAN FROM SATELLITE ALTIMETRY AND NUMERICAL-MODELS

We have used satellite altimetry to measure the statistics of geostrop hic turbulence in a 3 500 km segment of the Antarctic Circumpolar Curr ent in the Southeast Pacific. The statistics were compared with compar able statistics of variability computed from a numerical model of the ocean circulation. We found that the distribution of eddies observed f rom space is very similar overall to the distribution calculated from the model. The two differ on small scales, especially near the crest o f the East Pacific Ridge. The model output tends to be more patchy, wi th large variability just upstream of the ridge crest, while space dat a are less patchy with large variability just downstream of the crest. The flow further downstream of the ridge was similar to that of a fre e jet. Variance of topography seen from space was about 80% of the var iance from the model; variance of current speed was about 120% of the variance from the model. Downstream of the ridge the typical size of e ddies increased with distance downstream consistent with theories for two-dimensional turbulence. The decay rate of turbulence downstream of the ridge crest calculated from the model output was nearly the same as that observed from space. The similar decay of turbulence seen in t he satellite and model data indicate that the overall influence of vis cosity may be well modeled in the numerical calculations. The zonal me an velocity downstream of the ridge agrees well with hydrographic data relative to a depth of 3000 m collected from 1963 to 1968. The positi on of the current maximum agrees within 0.5 degrees of latitude, and s peed is 25% faster than that calculated from hydrographic data. The di fferences are consistent with interannual variability of the current.