24 days of kitchen oceanography
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Topographic mixing
Why is there so much turbulence in the lower bottle?
Experiment 14:
We fill two bottles (one with walls that are as straight as possible, the other with a structured wall) one-third with oil, one-third with water, and the last third is left empty. Make sure to close the bottles as tightly as possible!
If the bottles are now placed on the sides and only slightly tilted, we see that the structures in the wall cause large waves at the interface between water and oil. While in the other bottle this boundary layer changes its slope but by and large remains flat. The tilting of the bottle creates a wave which we can think of as a tidal wave. But that wave does not lead to mixing by itself. Only when it encounters structures, like oceanic ridges (the structure in the wall of a bottle), turbulence is created.
In this experiment, we used water and oil rather than different water masses because mixing between the two is reversible and we can run this experiment as often as we like, rather than once.