GULF-STREAM STRUCTURE, TRANSPORT, AND RECIRCULATION NEAR 68-DEGREES-W

An analysis of the structure and transport of the Gulf Stream is under taken using direct current meter observations from a 13-mooring array deployed near 68 degrees W from June 1988 to August 1990. The analysis is based on a ''stream-coordinate'' approach, in which velocities are rotated into a local, downstream coordinate frame and averaged accord ing to their relative cross-stream location within the current. The pi cture so obtained represents the average synoptic structure of the Gul f Stream, rather than the Eulerian-averaged structure in which the cur rent is weakened and broadened by lateral meandering of the current an d adjacent recirculations. Many familiar features of the Gulf Stream a re reproduced in the analysis, including an asymmetric velocity profil e with larger shear on the cyclonic (shoreward) side of the current, a n offshore displacement of the velocity core with depth, and a subsurf ace velocity maximum on the offshore side of the current. Westward rec irculations are also seen on both sides of the Gulf Stream. Maximum do wnstream speeds at the axis of the Gulf Stream reach approximately 2.0 m/s at the surface and 0.7 m/s at 1000 m, roughly twice the correspon ding Eulerian-averaged values. The analysis also reveals a deep extens ion of the Gulf Stream at 3500 m depth with a width of 130 km and aver age speeds of 3-4 cm/s. The transport of the Gulf Stream in the stream -coordinate frame is 113 +/- 8 Sv, approximately 30% larger than the E ulerian-averaged transport of 88 Sv. On the basis of these results and other recent studies the downstream transport increase of the Gulf St ream and the inflow structure to the Gulf Stream are reconsidered. It is concluded that approximately 30 Sv, or over half of the transport i ncrease between Cape Hatteras and 68 degrees W, is fed by inflow from the northern side of the Gulf Stream and that this inflow is concentra ted near Cape Hatteras and 68 degrees W, where the Gulf Stream flows s teeply across isobaths converging from the north.