Evolution of an isolated region in a stratified fluid

This paper reports an experimental study on the evolution of an isolated turbulent region in an otherwise quiescent linearly stratified fluid. A turbulent patch was generated by pulsed horizontal injection of a small volume of fluid. It was found that the turbulent blob thus produced initially grows as in a nonstratified fluid for a nondimensional time period of Nt ˜ 4 – 5 (with N the buoyancy frequency), attains a maximum height, and then physically collapses slowly to form a planar, quasi-two-dimensional dipole pattern. The timescale for the physical collapse of the blob was found to be much larger than that of the turbulence collapse. Scaling arguments are presented to explain the evolution of the turbulent region, and the experimental results are compared with the model predictions