Rayleigh-Taylor Instability Between Unequally Stratified Layers

While the classical Rayleigh-Taylor instability between two homogeneous incompressible layers continues to accelerate until the influence of boundaries become dominant, when the instability grows between two otherwise stably stratified layers, the initial growth is limited by the stratification and can be arrested before the instability reaches the boundaries. Here we study the intermediate case where one of the two layers is stably stratified and the other homogeneous, thus introducing an asymmetry where the instability grows into one layer without restriction, but is eventually arrested by the stratification in the other layer. Experimental measurements of the density and velocity fields show both similarities and differences compared with the two limiting cases in terms of both the evolution of the height of the mixing zone and the final stratification achieved.