North Atlantic Subtropical Gyre

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The basin-wide clockwise circulation of the North Atlantic, driven by the trade winds on its southern flank and the mid-latitude westerlies on its northern flank. The two wind belts push surface water toward the centre of the basin through Ekman transport; the water piles into a broad mound roughly a metre high and the resulting pressure gradient, balanced against the Coriolis force, sets the gyre turning. Harald Sverdrup showed in 1947 that the interior flow is fixed by the curl of the wind stress rather than by the wind direction. The gyre is slow and broad over most of its area and fast and narrow only on its western edge, where the Gulf Stream runs.