STRUCTURE OF THE GULF-STREAM AND ITS RECIRCULATIONS AT 55-DEGREES-W

Two years of direct current and temperature observations from an array of 13 current meter moorings deployed near 55 degrees W as part of th e SYNOP (Synoptic Ocean Prediction) Experiment have been used to explo re the spatial and temporal variability of the Gulf Stream from three points of view. In the geographic reference frame, mean eastward veloc ities were observed from the surface to 4000 m. There was no evidence of westward flow south of the eastward jet, suggesting that the Worthi ngton recirculation gyre was located south of the array during this ti me period. Westward flow was observed north of the jet only at 4000 m, where it had a magnitude comparable to the mean Gulf Stream (5-10 cm s(-1)). These data also indicate that the mean eastward jet is much mo re vertically aligned than was depicted in an earlier picture construc ted from noncontemporaneous observations. In the Lagrangian, or stream wise, reference frame, it was found that, at the thermocline level, th e width of the ''average synoptic'' Gulf Stream and the velocity struc ture remain virtually unchanged between Cape Hatteras (73 degrees W) a nd 55 degrees W, in spite of large amplitude meandering. The barotropi c velocity component of the average synoptic stream increases fivefold over this distance, and the baroclinic component weakens. The norther n recirculation appears more clearly in the stream coordinate frame as a 130-km wide barotropic flow with peak westward velocities of about 8 cm s(-1). South of the stream, there was no evidence of westward flo w, even in the stream coordinate system. Finally, a consideration of e ddy-mean flow interactions in terms of the eddy energy equations shows that at the thermocline level, there were no significant cross-gradie nt fluxes of hear or momentum, supporting the notion that 55 degrees W is at a maximum in eddy energy. At 4000 m, there was some indication of upgradient heat and momentum fluxes in the Gulf Stream, consistent with decreasing eddy energy following the mean flow to the east. These results point to the region between 55 degrees W and the Tail of the Grand Banks (50 degrees W) as the site of eddy energy decay in the Gul f Stream system.