Simultaneous velocity–density measurements of downslope density clouds

We present results from laboratory experiments of the downslope propagation a finite volume released gravity current by means combined PIV/PLIF measurements. The experimental data were used to estimate global characteristics current, such as speed, lateral surface and buoyancy, revealing that thermal theory is robust model can predict quantities properly, especially models Beghin et al. (1981), Maxworthy (2010) theoretical Dai (2013a). collected allowed also for determination entrainment rates based on turbulent fluxes instead using variation flux, regions entrainment/detrainment have been identified. support previous observations mechanism responsible buoyancy loss cloud its consequent deceleration down slope, large scale recirculation vortex at back cloud. A very complex interior structure observed, with variety processes taking place, large-scale convectively unstable itself, small-scale motions inside head close bottom boundary shear (Kelvin–Helmholtz) instabilities between ambient water. synoptic velocity density measurements test existent parametrizations fluxes, quantified in 2D fields high spatial resolution. Results confirm parametrization laws assumption constant diffusivity or mixing length do not apply clouds due their heterogeneity. Hence, diffusivities flows should be scalar avoid problem heterogeneity takes into account different sources turbulence production, e.g. energetic considerations compare terms having definite exchange energy acts source sink.