A Spectrum of Convective Self-Aggregation Based on Background Rotation

Abstract

High-resolution modeling reveals a tendency for deep convection to spontaneously self-aggregate from radiative-convective equilibrium. Self-aggregated convection takes different forms in nonrotating versus rotating environments, including tropical cyclones (TCs) in the latter. This suggests that self-aggregation (SA), and the relative roles of the mechanisms that cause it, may undergo a gradual regime shift as the ambient rotation changes. We address this hypothesis using 31 cloud-resolving model simulations on f-planes corresponding to latitudes between 0.1° and 20°, spanning a range of weakly rotating environments largely unexplored in prior literature. Simulations are classified into three groups. The first (low-f, 0.1°–5°) is characterized by the growth of several dry patches. Surface enthalpy flux feedbacks dominate in this initial growth phase, followed by radiative (primarily cloud longwave) effects. Eventually, convection takes the form of either a nonrotating band or a quasi-circular cluster. In contrast, the 9°–20° (high-f) group dries less rapidly in early stages, though enhanced surface flux effects form a moist anomaly that undergoes TC genesis. The TC then acts to dry the remainder of the domain. Finally, a set of 6°–8° (medium-f) simulations fails to fully self-aggregate, producing convection across most of the domain through the full 100-day simulation. The combination of relatively weak diabatic feedbacks and a negative advective feedback prevents SA from completing in this group. The advective feedback becomes more negative with increasing rotation, but high-f simulations compensate by having sufficiently strong surface flux feedbacks to support TC genesis.