DETERMINING THE MEAN GULF-STREAM AND ITS RECIRCULATIONS THROUGH COMBINING HYDROGRAPHIC AND ALTIMETRIC DATA

The altimetric data from the first 2.5-year Geosat Exact Repeat Missio n were used to estimate the mean sea surface height (SSH) field in the region of the Gulf Stream and its recirculation gyres. Assuming the i nstantaneous surface velocity field is composed of an eastward flowing jet and two westward recirculating flows, we used the time-varying su rface data from the altimeter to determine the shape of the along-trac k mean SSH profiles and the historical hydrographic data to constrain the net SSH difference across the Gulf Stream system. The two-dimensio nal mean SSH field was determined by objectively mapping the mean heig ht profiles along the ascending and descending tracks. The SSH jump ac ross the mean Gulf Stream has a maximum of 1.15m around 65 degrees W a nd drops to an almost constant 0.9m downstream of the New England Seam ount Chain (NESC). While the SSH jump associated with the mean norther n recirculating flow is mostly uniform, we found that the Gulf Stream' s southern recirculation has two local gyres that are separated by the NESC. An attempt was then made to estimate the mean deep circulation in this region by comparing the mean SSH field derived from the altime try data and the surface dynamic height field based on the historical hydrographic data. Despite the large uncertainties, the mean deep how pattern thus estimated agrees favorably with the overall circulation p attern from the long-term current meter observations. Like the well-de fined northern recirculation gyre, we found that a continuous southwar d flow exists along 57.5 degrees W, which follows closely along the de ep layer potential vorticity contours. To the south of the Gulf Stream , the deep circulation consists of two separated recirculation gyres; the recirculation gyre to the east of the NESC appears to be trapped a round the Corner Rise.