Convective aggregation in realistic convective-scale simulations

To investigate the real-world relevance of idealized-model convective self-aggregation, five 15 day cases of real organized convection in the tropics are simulated. These include multiple simulations of each case to test sensitivities of the convective organization and mean states to interactive radiation, interactive surface fluxes, and evaporation of rain. These simulations are compared to self-aggregation seen in the same model configured to run in idealized radiative-convective equilibrium. Analysis of the budget of the spatial variance of column-integrated frozen moist static energy shows that control runs have significant positive contributions to organization from radiation and negative contributions from surface fluxes and transport, similar to idealized runs once they become aggregated. Despite identical lateral boundary conditions for all experiments in each case, systematic differences in mean column water vapor (CWV), CWV distribution shape, and CWV autocorrelation length scale are found between the different sensitivity runs, particularly for those without interactive radiation, showing that there are at least some similarities in sensitivities to these feedbacks in both idealized and realistic simulations (although the organization of precipitation shows less sensitivity to interactive radiation). The magnitudes and signs of these systematic differences are consistent with a rough equilibrium between (1) equalization due to advection from the lateral boundaries and (2) disaggregation due to the absence of interactive radiation, implying disaggregation rates comparable to those in idealized runs with aggregated initial conditions and noninteractive radiation. This points to a plausible similarity in the way that radiation feedbacks maintain aggregated convection in both idealized simulations and the real world. Plain Language Summary Understanding the processes that lead to the organization of tropical rainstorms is an important challenge for weather forecasters and climate scientists. Over the last 20 years, idealized models of the tropical atmosphere have shown that tropical rainstorms can spontaneously clump together. These studies have linked this spontaneous organization to processes related to the interaction between the rainstorms, atmospheric water vapor, clouds, radiation, surface evaporation, and circulations. The present study shows that there are some similarities in how organization of rainfall in more realistic computer model simulations interacts with these processes (particularly radiation). This provides some evidence that the work in the idealized model studies is relevant to the organization of tropical rainstorms in the real world.