Experiments on layer formation in stratified shear flow

We discuss the experimental methodology and present the results of several experiments on the onset and growth of instabilities in stratified shear fl ow. Our results include the assessment of the effective diffusivity prior t o the development of the Kelvin-Helmholtz (K-H) type instability and the me asurement of the velocity field. This allows us to determine that the onset of the instability takes place when the Richardson number is close to 0.25 , this value slightly decreasing with increasing initial interface thicknes s. The formation of a fine layered structure at the interface is suggested by density profiles taken immediately after the generation of K-H billows, but the size of the full interface as well as the layers themselves decreas e in the following few seconds. We hypothesize that the time scale of the K -H billows in our laboratory experiments is so short that there is no time for added mixing to further distribute and smoothen the initial layer struc ture.