Figure 1: Note the similarity of these imagined circulation fields for the atmosphere and ocean. Atmospheric pressure contours show a low over Canada and a high over southeastern United States. Arrows indicate direction of flow deduced from the geostrophic relation (that between horizontal pressure variations and horizontal currents), with higher speeds where the contours are closer together. Contour lines in the western North Atlantic illustrate an analogous field, the dynamic height at the sea surface. The compressed bundle emerging from the south off the coast of Florida is the Florida Current, which initiates the Gulf Stream system. The ocean surface is about a meter higher in mid basin than it is inshore of the Gulf Stream, and this drives the flow, indicated by arrows. Contours that peel off to the south indicate a partial clockwise circulation pattern around the high-elevation region, analogous to the clockwise flow around high pressures in the atmosphere.