The Essential Role of Cloud-Radiation Interaction in Nonrotating Convective Self-Aggregation

Convective self-aggregation in radiative-convective equilibrium (RCE) is a phenomenon of significant interest because of its potential relevance to the organization of tropical storms. However, some previous theories on RCE instability neglected or simplified cloud-radiative interaction in theoretical models and suggested that water vapor-radiation feedback is responsible for destabilizing a homogeneous RCE state. Here, through numerical experiments of nonrotating RCE, we first confirm that the predictions from these theories are valid insomuch that dry patches can form in an initially homogeneous domain with uniform sea-surface temperature when cloud-radiation interaction is suppressed or eliminated. However, sustained growth of those dry patches is not guaranteed. Developing deep convective circulation can engulf dry patches, and water vapor feedback is not sufficient for overcoming this barrier. Only when the early-stage cloud radiative forcing is sufficiently strong can self-aggregation fully develop. Therefore, cloud-radiative feedback is essential for the eventual realization of self-aggregation in nonrotating RCE.