The Gravity Currents

The movies/photos on this page relate to our work on the dynamics of gravity-driven surface currents in rotating system. The goal is to simulate coastal currents developing from estuarine discharges into the ocean. In the Ocean such currents can be affected by the background rotation associated with the rotation of the Earth. The discharged, fresh river water is buoyant in comparison to the denser ocean water. Hence, a surface current is established. This is restricted to flow along the coast as a consequence of the action of the Coriolis force arising from the background rotation. We have been looking at the speed, the depth and the width of the current. These are studied a function of the background rotation rate, the density difference between fresh water and ambient ocean water and the volumetric discharge rate at the source. A summary of our results was submitted to the Journal of Fluid Mechanics in December 2005.

Below you can see a few examples of what the currents typically look like. However, be aware the mpg files are fairly large (3 MBytes each) and it may take a while to upload them. If you are patient enough and succeed in getting to the viewing stage then what you will see is as follows....

You are looking down on to a circular tank (diameter 1m). The tank is placed on a rotating turntable . The tank is filled with clear salt water. The source where fresh water is released is located about at the 7 o'clock position. When the source is switched on you will see (dark) fresh fluid being discharged which then begins to flow along the wall of the tank. Remember that you are viewing the flow from within in the rotating system; so don't get dizzy. The current moves anti-clockwise which is the same direction in which the turntable rotates. In technical terms the current propagates cyclonically around the wall of the tank ( Example 1 , Example 2 , Example 3 ).

We have also repeated the same type of experiments on a MUCH larger turntable at the Coriolis facility in Grenoble, France. The Coriolis Facility is the world's larges and most sophisticated turntable facility to study oceanographic flows. The tank of the Coriolis Facility has a diameter of 13 metres!

Here are some pictures from the experiments at the Coriolis facility. The first picture shows a stable current , while this picture shows a current that has developed instabilities . Here you can see some measurement probes used to monitor the internal flow velocity . And here a last picture showing Eddy DeCay , while being busy setting up the experiments. We had to paint the whole bottom of the tank white for visualization purposes. Eddy DeCay had great fun squirting paint all over everyone!