EVOLUTION OF AN ISOLATED TURBULENT REGION IN A STRATIFIED FLUID

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