Simple models for convective cold pool interaction

Large-Eddy Simulations (LES) show that the presence of cold pools can result in a growth of scales in moist convection. In the diurnal cycle over land, the distance between clouds grows rapidly after the onset of precipitation, while rainfall produced by each cell increases. Here, we first explore the role of cold pool interactions in LES in more detail: using a particle method to track cold pool gust fronts, we characterize the basic collision modes between cold pools. Convergence at low levels appears important for cloud triggering, and this convergence is particularly strong in regions where three cold pools collide under specific conditions. We discuss recently developed theoretical models that can represent these cold pool interactions. The simplest of these models is a parameter-free formulation where the cold pools are represented as circles which increase in radius, and new triggering occurs as a result of interactions between these expanding circles. Even this geometrical model results in clustering of convection and scale growth. We discuss our findings with regards to the diurnal cycle of convection, and comment on applicability of the model to radiative convective equilibrium and extreme rainfall. We also discuss the implications for atmospheric models in which cold pools are absent or poorly represented on the grid scale.