A wind stress is applied to the surface to cause mixing.
This is an experiment that I have been wanting to do for a long time, but somehow it never worked out before. But last night Martin and I finally ran it!
We ran two experiments, one after the other.
In the first one, we took a tank full of freshwater, added dye droplets and switched on a hair dryer to force mixing through the wind stress. After about a minute, the tank was fully mixed.
In the second experiment, we created a salt stratification: salt water with approximately 35 psu, and freshwater. We then added the dye droplets. The droplets never penetrated into the salty layer but instead layered in at the interface between the two layers. We then added the wind stress.
After a minute, the surface layer was well mixed, but there was no mixing penetrating into the bottom layer. To fully mix the whole depth, the wind forcing ran for 86 minutes.
Watch a short movie below and a movie containing the full time lapse even further down!