Convective Self-Aggregation on Short Time Scales: Cycling Clusters

Convective organization over a 500 km periodic domain is examined using a cloud resolving large-eddy simulation model with a full radiative transfer scheme and coupled simple mixed layer ocean. Simulations are conducted with moderate shear over a 8 day period using an initial sounding based on the average conditions observed from the RV Revelle during the DYNAMO experiment. The atmospheric model is coupled to a column ocean simulated with the K-profile parameterization. Simulations show that after 4 days, convection organizes into cloud clusters controlled by a domain-scale internal wave propagating at approximately 25 m/s. Clusters have a lifecycle of about 3-4 hours with new convection forming over different areas of the domain. Overall, convection exhibits a diurnal cycle with a maximum in the early morning before simulated sunrise. The cluster lifecycle appears to be controlled by cold air accumulation in the marine boundary layer, which generates a divergent wind field, cutting off moist static energy. Patterns of fresh water and sea-surface temperature do not have a significant impact on the cluster formation or decay.