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Figure 1. We are looking from above at an upstream region and a channel. These are held in a larger two-meter diameter cylindrical catch basin on a rotating turntable. The very flat channel bottom was produced using plate glass, painted black, carefully leveled and elevated about 20 cm above the bottom. Water lying under the atmosphere was used for this experiment. Depth of the water over the channel was deep enough (two cm, say) so that the Rossby Radius of the water layer was less than the width of the channel. Sides were attached to the flat bottom. The marks on the channel wall (to the right of the direction of flow, which is at the bottom of this view) are cm marks. The channel was connected to a deeper upstream region on the left with a bottom sloping up to the channel. Water was pumped into the upstream region until it filled the basin and spilled out through the channel. The source is located near the bottom left of this photograph. Instead of the water flowing directly up the sloping bottom to the channel, it flows to the other upstream wall at the top left of this photograph and then moves along that wall to the channel. Once it arrives at the flat region the water veers to the right-hand wall of the channel (looking downstream). The result is that there is a region of almost zero flow in the upstream region that lies between the upstream current and the current in the channel. This region corresponds to upstream gyres predicted theoretically.
Figure 2. We are looking from the side of a cylindrical tank filled with kerosene in the bottom and a water-alcohol mixture at the top. An upstream region is separated from downstream by a vertical wall with a channel. Bottom fluid is pumped into the bottom of the upstream basin and it returns through the channel. In this view, the returning flow is coming toward us. This illustrates three features of such flows: 1. Upstream circulation, as shown by the circular front. 2. Tilt of the interface in the passage. 3. Turbulence in the downstream basin.
Figure 3. This shows a side view of a current of blue dense water in clear rotating ambient water. The current emerges from the passage, flows down the slope, bends to its right as it flows because of rotation and develops roll waves.
Figure 4. This is a top view of a rotating current of dyed dense water in clear ambient water over a sloping bottom. The shallow end is at the top of the picture, and the source of the current was located at the top right. The current breaks up into eddies. These consist of a lens of dense water lying on the sloping bottom. The lenses drift toward the left in this picture, and they have cyclonic circulation in the clear water overhead. This circulation is visible as time-exposure streaks from surface pellets as the lens drifts over the black bottom. The bottom picture is some tens of seconds after the top.
Laboratory studies relevant to overflow dynamics
J.A. Whitehead

Saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next, depending on the source of bottom water. We show four laboratory studies that have been designed to illuminate dynamics of such flows in the ocean. As expected, processes due to effects of rotation are found when Rossby radius is less than a typical lateral length-scale.

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