A Physically Based Definition of Convectively Generated Density Currents: Detection and Characterization in Convection-Permitting Simulations

Rochetin, Nicolas ; Hohenegger, Cathy ; Touzé-Peiffer, Ludovic ; Villefranque, Najda

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In this study, a conceptual model to define convective density currents is proposed. Based on theory, observations and modeling studies, we define convective density currents as 3D coherent structures with an anomalously cold core, an adjacent wind gust, and a vertical structure made of two layers: a well-mixed one near the surface and a stratified one above. With this definition, a methodology is proposed to identify and label individual convective density currents in convection-permitting simulations. The method is applied to four distinct cloud scenes taken from a convection-permitting simulation. Our methodology reveals new dynamic, thermodynamic, and geometric features related to the density currents' imprint on the planetary boundary layer. The method is found to be (i) relevant in distinct convective regimes, (ii) relevant in land and oceanic situations, and (iii) adapted to both Cloud Resolving Models and Large Eddy Simulations. It also provides proxies such as the number, the spatial coverage, the mean radius, and the mean velocity of convective density currents, from which a detailed analysis of their role in the life-cycle and spatial organization of convection could be performed in the near future.</p>

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