When swimming in a fjord, where rivers etc. can produce a fresh water layer at the surface, one can often see an optical effect of mixing two water masses with different refractive indices. (I've measured salinity with a CTD, and there can for example be about 15 ppt salt at the surface and 25 at a meter depth.)
The same optical effect can be seen if you put sugar in tea, let it dissolve slowly at the bottom of the cup, and then stir the cup gently.
My question is: Is this schlieren? The wikipedia page on schlieren talks mainly about a somewhat involved measurement technique, and all the example images are of far more esoteric situations.
