Modulation of Tropical Convection‐Circulation Interaction by Aerosol Indirect Effects in Convective Self‐Aggregation Simulations of a Gray Zone Global Model

Disentangling the response of tropical convective updrafts to enhanced aerosol concentrations has been challenging. Leading theories for explaining the influence of aerosol concentrations on tropical convection are based on the dynamical response of convection to changes in cloud microphysics, neglecting possible changes in the environment. In recent years, global convection-permitting models (GCPM) have been developed to circumvent problems arising from imposing artificial scale separation on physical processes associated with deep convection. Here, we use a global model in the convective gray zone that partially simulates deep convection to investigate how enhanced concentrations of aerosols that act as cloud condensate nuclei (CCN) impact tropical convection features by modulating the convection-circulation interaction. Results from a pair of idealized non-rotating radiative-convective equilibrium simulations show that the enhanced CCN concentration leads to weaker large-scale circulation, the closeness of deep convective systems to the moist cluster edges, and more mid-level cloud water at an equilibrium state in which convective self-aggregation occurred. Correspondingly, the enhanced CCN concentration modulates how the physical processes that support or oppose convective aggregation maintain the aggregated state at equilibrium. Overall, the enhanced CCN concentration facilitates the development of deep convection in a drier environment but reduces mean precipitation. Our results emphasize the importance of allowing atmospheric phenomena to evolve continuously across spatial and temporal scales in simulations when investigating the response of tropical convection to changes in cloud microphysics. How does air pollution affect thunderstorm intensity over the tropical ocean? Past studies have proposed different pieces of evidence but generally neglect the interplay between the development of thunderstorms and the long-range movement of air that redistributes the Earth's thermal energy and moisture. Here, we address this question by investigating results from idealized numerical experiments in which a global domain is used to simultaneously simulate the response of individual thunderstorms and large-scale air motion to pollution. We found that pollution makes the thunderstorms keep less moisture in their surroundings, limiting the intensity of thunderstorms and weakening the large-scale air motion that supplies moisture to thunderstorms. Our results suggest that the interplay between the development of thunderstorms and the long-range movement of air is crucial in determining the effects of pollution in the tropical atmosphere. A global model with horizontal grid length in the convective gray zone is used to investigate aerosol indirect effects Pollution leads to weaker large-scale circulation, the closeness of convection to the moist cluster edges, and more mid-level cloud water Pollution facilitates deep convection development in a drier environment but reduces mean precipitation