THE TRANSITION FROM DENSITY-DRIVEN TO WAVE-DOMINATED ISOLATED FLOWS

An isolated fluid mass travelling horizontally in a stratified layer i s a phenomenon described alternatively as a detached gravity-current h ead or a strongly nonlinear solitary wave. A. key feature of this flow is the transport of mass. Laboratory experiments examine the transiti on in time from a regime in which the flow is density driven, to one i n which it is wave dominated. A simple means of creating this transiti onal regime, an isolated how that exhibits both density and wave effec ts, is achieved by dropping a thermal into a linearly stratified layer . This transitional regime is called an 'isolated propagating flow'. P arameters for which the transitional regime occurs are identified. Par ticle-tracking studies reveal the vertical flow structure. There is an upper zone that is wave dynamical, and a lower zone in which transpor t of mass occurs. The transported mass slowly leaks out, until the phe nomenon resembles a weakly nonlinear solitary wave. The experiments mi mic a thunderstorm microburst impacting a temperature inversion, which has aviation safety implications. In the ocean, cracks in the ice cap (polar leads) cause similar flows impacting the thermocline.