4 The Gulf Stream System

N. P. Fofonoff In the two decades since the first publication of Stommel's (1965) monograph on the Gulf Stream, our knowledge of the Gulf Stream System has been expanded dramatically through the development and application of new, powerful measuring techniques. Multiple ship surveys of the type organized by Fuglister (1963) provided the first systematic descriptions of the spatial structure between Cape Hatteras and the Grand Banks that included the surrounding slope waters to the north and the Sargasso Sea waters to the south of the Gulf Stream. Several major theoretical and interpretative studies grew from the base of data and descriptions provided by this study. During the same period, instrumented buoys, both moored and drifting, were beginning to reveal some of the complexities of the subsurface and deep fields of temperature and currents. Among the new techniques implemented in the 1960s was infrared-radiation imaging to map the thermal patterns of the ocean surface from satellites orbiting the earth (Legeckis, 1978). The two-dimensional surface thermal maps that have been obtained have added rich detail to our knowledge of the strongly varying thermal structure associated with the Gulf Stream throughout its path. Yet, despite these advances in our ability to measure, our understanding of the dynamic mechanisms by which the Gulf Stream forms, develops in intensity, decays, and finally merges into the largescale circulation of the North Atlantic have not evolved as satisfactorily. Even the mechanism controlling the position of the Gulf Stream after leaving the continental shelf at Cape Hatteras has not yet been firmly established. Is the Gulf Stream controlled by bottom topography, by the distribution of mean wind stress, or by a mechanism yet to be determined? The dynamics by which meanders of the Gulf Stream amplify and develop into large rings and eddies and the subsequent movement and evolution of these entities are not well understood. In spite of the impressive progress of the past decades, much remains to be done to resolve and understand the particular mechanisms that determine the character and behavior of the Gulf Stream along its entire path from the Gulf of Mexico into the central North Atlantic. In preparing material for this review, I concluded that my initial plans for a comprehensive discussion of the literature since 1958 were unrealistic. As over 200 references plus numerous technical reports and articles were identified, it became obvious that only a few aspects of the Gulf Stream System could be covered in a single short review. Given the necessity for choice, it is clear that the selection must reflect my preferences, interests, and perhaps, biases. I hope my effort to trace particular lines of research in the literature