The Distinction Between the Gulf Stream and Its North Wall.

Downstream of Cape Hatteras, the Gulf Stream (GS) is bounded to the north by a sharp temperature front known as the North Wall (NW). Previous studies have generally assumed that variations of the NW and GS are equivalent. Using satellite sea surface height to identify the GS and the 15 °C isotherm at 200‐m depth to represent the NW, this paper examines their similarities and differences during 1993–2016. The NW and GS are geographically close and vary similarly only to the west of 71°W. Downstream of that, they rapidly diverge—and the variances of their latitudes increase by more than a factor of 2—as the GS flows past the New England Seamounts. Evidence is presented to show that the difference in properties of the NW and the GS is related to the presence of mesoscale eddies in the region separating them. Plain‐Language Summary: To the east of Cape Hatteras where the Gulf Stream leaves the continental shelf, a sharp gradient in ocean temperature, known as the North Wall, is seen just north of the current. Fluctuations in the position of the North Wall have large impacts in the distribution of heat in the North Atlantic and on plankton populations. There is a widespread assumption in the literature that variations of the North Wall and the Gulf Stream are similar. Results presented in this paper show that variations of these two features become increasingly different as the current proceeds eastward and the divergence in their properties is due to the presence of turbulent eddies, which arise after the Gulf Stream interacts with the New England Seamounts. These results suggest that recognition of distinct behaviors of the Gulf Stream and the North Wall is needed for a better understanding of their dynamics and their impact on climate. Key Points: The Gulf Stream and its North Wall are close to each other west of 71°W but depart sharply in their properties farther downstreamDifferences in the behaviors of the Gulf Stream and the North Wall are related to mesoscale eddies between themRecognition of distinct properties of Gulf Stream and the North Wall is necessary for understanding their dynamics and impact on climate [ABSTRACT FROM AUTHOR]