Wind-driven circulation in one- and two-layer oceans of variable depth

Abstract

The effect of bottom topography is studied for homogeneous and two-layer oceans with Ekman-type dynamics. In the case where friction is important only at a lateral boundary explicit solutions are obtained. Cases in which friction becomes important also in the interior are discussed qualitatively. Essential differences are found between the solutions for the homogeneous and the two-layer oceans. In the homogeneous ocean a western or an eastern boundary current occurs when ?/?y(f/H) is positive and negative, respectively (f is the Coriolis parameter, H the depth, y a northward coordinate), and there is a Sverdrup type interior circulation modified by bottom topography. This case has been discussed previously in the literature. In the two-layer model with the upper layer thin compared to the lower layer the motion in the lower layer becomes small. The upper layer solution is similar to the one-layer solution given by Stommel (1948) with a western boundary current, with some modification due to finite distortions of the interface. In the lower layer there is also a western boundary current. If ?/?y(f/H) > 0 this current recirculates at the western boundary and no interior motion occurs. If ?/?y(f/H) < 0 an eastern boundary current as well as an interior circulation is added. In both the homogeneous and the two-layer models free jets can cross over the ocean along a critical line, where ?/?y(f/H) = 0. If a region with closed f/H -contours exists in the interior a corresponding gyre is added to the solution. The circulation in this gyre becomes very strong for the homogeneous ocean, weak for the two-layer ocean. In the North Atlantic f/H increases northward, and closed contours exist only in a region at the Azores. According to the two-layer model the deep motion should be confined to a recirculating western boundary current. A deep anticyclonic gyre could possibly be found near the Azores with a jet connecting to the western boundary current along the 2 km depth contour. DOI: 10.1111/j.2153-3490.1968.tb00347.x