EDDY KINETIC-ENERGY AND MOMENTUM FLUX IN THE SOUTHERN-OCEAN - COMPARISON OF A GLOBAL EDDY-RESOLVING MODEL WITH ALTIMETER, DRIFTER, AND CURRENT-METER DATA

The ability of a seasonally forced high-resolution global ocean general circulation model to simulate eddy variability and associated energy and momentum transfer processes in the Southern Ocean is assessed by comparing model statistics with observations. The observations include Geosat altimeter data analyzed for surface velocity variance at satellite ground track crossover points, current-meter data from the Agulhas and Campbell plateaus, and surface drifter data in the Tasman Sea. In western boundary currents and energetic regions of the Antarctic Circumpolar Current model eddy kinetic energy is lower than observed by typically a factor of 4, and in less energetic regions by a factor of 10. Differences in the location and extent of energetic regions are related to smoothness of the model bathymetry and other features of the model configuration. Eddy momentum flux divergence and eddy to mean kinetic energy conversion at the surface are diagnosed from the model. These show regions where eddy activity accelerates the mean flow through instability processes. Observational estimates of these terms are computed using mean flow gradients from hydrography climatology and altimeter eddy statistics. Several features of the spatial distribution of the observational estimates are consistent with the model and suggest that future calculations of mean currents from altimeter data will allow direct computation of eddy to mean current momentum and energy conversion terms.