The meandering Gulf Stream as seen by the Geosat altimeter: Surface transport, position, and velocity variance from 73° to 46°W

Abstract

The surface geostrophic velocity field for the Gulf Stream region was analyzed for the position, structure and surface transport of the Gulf Stream for 2.5 years of the Geosat altimeter Exact Repeat Mission. Synthetic data using a Gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents. Most of cross‐track velocity variance was due to the meandering of the Gulf Stream, rather than to rings or complicated velocity profiles, which suggested that the simple model parameters are an efficient description of the Gulf Stream fluctuations. An analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the Gulf Stream connected by a narrow transition region coincident with the New England Seamount Chain. The upstream region was characterized by relatively straight Gulf Stream paths, long Eulerian time scales and eastward propagating meanders. The downstream region had more large meanders, no consistent propagation direction and shorter Eulerian time scales. A 25% reduction in surface transport occurred in the transition region, with a corresponding reduction in current speed and no change in Gulf Stream width. A significant anomaly in surface transport near 69°W suggested the existence of small‐scale recirculation gyres there. The highest‐variance empirical orthogonal functions of position and surface transport were significantly correlated, with larger surface transports leading more northerly positions by a month.