Wind-driven entrainment in a stably stratified fluid

Experiments on mixed-layer deepening in a straight wind flume initially containing a two-layer fluid were carried out. In order to simulate an effectively unlimited water body, or a situation where the presence of end walls is not yet noticeable, the water from the upper layer was withdrawn at the downstream end, and supplied again at the upstream end in part of the experiments. Upper layer depths, and mean density and velocity profiles were measured for overall Richardson numbers (based on the surface friction velocity) ranging from 22 to 1090. The integral entrainment model of Spigel and Imberger 1980 was extended with terms accounting for shear production, and mixing caused by recirculation and side-wall friction. Model constants were derived from the experiments and the extrapolation to the situation where recirculation and side-wall influence are absent is discussed.