Pattern and velocity of propagation of the global ocean eddy variability

Satellite altimeter data are used to study the characteristics of the horizontal propagation of eddy variability of the global oceans. Decade-long time series of sea surface height is analyzed for finding the maximum cross correlation with neighboring time series within a window of space and time lags. The space and time lags corresponding to the maximum correlation allow an estimate of the propagation velocity of the eddy variability that dominates the variance of sea surface height anomalies. The method cannot distinguish the various forms of eddy variability: isolated eddies and fronts, the meandering of ocean currents, or planetary waves. However, the results provide, at a given location of the global oceans, a uniquely determined propagation velocity that represents a time-averaged description of the tendency of the movement of the local eddy variability. The propagation velocity is highly inhomogeneous in space. Outside the equatorial zone, the zonal propagation is intrinsically westward, modified by ocean currents, which could reverse the zonal propagation to eastward in regions like the Gulf Stream and the Antarctic Circumpolar Current. At midlatitudes and high latitudes, the propagation pattern is highly affected by the path of ocean currents and the shape of bottom topography. At tropical latitudes, the meridional propagation is convergent toward the equator in the western basins and divergent away from the equator in the eastern basins. Comparison with the simulations of an eddy-permitting ocean general circulation model shows overall agreement, especially in the latitudinal variation of the zonal propagation velocity. The result suggests that the model has captured the essence of the dynamics governing the propagation of ocean eddy variability.