The diurnal path to persistent convective self-aggregation

Abstract

Clustering of tropical thunderstorms constitutes an important climate feedback because it influences the heat radiated to space. Convective self-aggregation (CSA) is a profound modelling paradigm for explaining the clustering of tropical oceanic thunderstorms. However, CSA is hampered in the realistic limit of fine model resolution when cold pools -- dense air masses beneath thunderstorm clouds -- are well-resolved. Studies on CSA usually assume the surface temperature to be constant, despite realistic surface temperatures varying significantly between night and day, even over the sea. Here we mimic oscillating surface temperatures in cloud resolving numerical experiments and show that, in the presence of a diurnal cycle, CSA is enabled by high resolutions. We attribute this finding to vigorous combined cold pools emerging in symbiosis with mesoscale convective systems. Such cold pools suppress buoyancy in extended regions ($\mathbf{\sim 100}$ km) and enable the formation of persistent dry patches. Our findings help clarify how the tropical cloud field forms sustained clusters under realistic conditions and may have implications for the origin of extreme thunderstorm rainfall and tropical cyclones.