Extraction of coherent eddy properties from individual particle trajectories, with application to the Gulf of Mexico
Abstract:
The eddy field is seen to be highly anisotropic, with anticyclones dominating for scales 50 km and larger, and cyclones dominating for smaller scales. Unsurprisingly, anticyclonic events generally match the properties of the large Loop Current Eddies, observed to form periodically in the eastern Gulf from pinch-off events of the Loop Current, and then to drift westward. At scales of 50 km and below, however, an energetic cyclonic eddy field is seen, but anticyclonic events are almost entirely absent. Highly nonlinear cyclonic events with radii consistently less than about 10 km are observed throughout the Gulf, apparently representing a rich field of surface submesoscale vortices; that these small and difficult-to-observe features are revealed is a testament to the sensitivity of the eddy detection method.
Between about 10 km and 50 km, the cyclonic eddy field is dominated by long-lived, highly nonlinear features. Those in the eastern basin are identified as Loop Current Frontal Eddies originating from the strong cyclonic shear zone on the periphery of the Loop Current. Similar features in the western basin are seen to originate from the same source, and then to propagate across the Gulf. Moreover, these sometimes merge with the long-lived Campeche Gyre in the southwestern Gulf, suggesting such eddy mergers may play an important role in the formation and maintenance of this feature. These results suggest that the primary source for intense mesoscale cyclonic variability throughout the entire Gulf of Mexico is the cyclonic shear zone on the outer edge of the Loop Current.