Variability and clustering of mid-latitude summertime convection: Testing the Craig and Cohen (2006) theory in a convection-permitting ensemble with stochastic boundary layer perturbations

AbstractThe statistical theory of convective variability developed by Craig and Cohen (2006) has provided a promising foundation for the design of stochastic parameterizations. The simplifying assumptions of this theory, however, were made with tropical equilibrium convection in mind. In this study, we investigate the predictions of the statistical theory in real-weather case studies of non-equilibrium summertime convection over land. For this purpose we use a convection-permitting ensemble in which all members share the same large-scale weather conditions but the convection is displaced using stochastic boundary layer perturbations. We find that the standard deviation of the domain-integrated mass flux is proportional to the square root of its mean over a wide range of scales. This confirms the general applicability and scale adaptivity of the Craig and Cohen (2006) theory for complex weather. However, clouds tend to cluster on scales of around 100 km, particularly in the morning and evening. This strong...