Contrasting Westward and Eastward Propagating Mesoscale Eddies in the Global Ocean

Although the zonal propagation of mesoscale eddies is intrinsically westward in oceans worldwide, eddies occasionally propagate eastward. Westward propagating eddies (WPEs) and eastward propagating eddies (EPEs) have distinctively different characteristics. In this article, the propagation features of WPEs and EPEs were studied using a combination of current, wind, and topographical data. We found that, except for in the North Atlantic, the energetic areas for WPEs and EPEs did not overlap. Furthermore, the propagation channels of WPEs and EPEs were located at different depths. The magnitude of change in current and wind stress simultaneously affected both the spread direction and velocity of eddies. The average translation speeds of eddies increased as subsurface current velocity increased, regardless of the angle between the direction of eddy propagation and flow. Compared with WPEs, increases in wind stress had little effect on the propagation speeds of EPEs. The directions of EPEs were more sensitive to changes in flow and wind speed. Even small changes in bathymetry slowed the propagation speeds of eddies. This topographical inhibition was biggest when the topographic gradients were around 0.02 and 0.04 for WPEs and EPEs, respectively. The propagation directions of EPEs were also sensitive to the surrounding terrain and tended to move along seamounts and ridges. These findings may refine eddy predictions and aid eddy observations in the future.