The Role of Cold Pools in Convective Aggregation over Tropical Oceans: A Two-Layer Stochastic Dynamic Model

Convective aggregation, which often leads to organized convective systems, is ubiquitous over tropical oceans and contributes substantially to both total and extreme precipitation in these regions. Cold pools, crucial processes linked to convection, are known to exert both suppressing and triggering effects on convective initiation, but their role in convective aggregation remains debated. As inspired by the previous study of Biagioli and Tompkins (2023), herea simple two-layer stochastic dynamic model for convective aggregation (see the figure below) is developed by coupling boundary-layer cold pool dynamics with free-troposphere moisture dynamics. The novelty of this model lies in two key aspects: the incorporation of compensating subsidence as a dynamic mechanism to maintain the total number of individual convective cells, and the coupling of the boundary-layer moist static energy (MSE) budget to represent both suppressing and triggering effects of cold pools. The results show that the suppressing effect of cold pools is essential for keeping individual convective cells separated, consistent with observations, while their triggering effect promotes larger cluster sizes and shorter aggregation timescales. The model is then applied to investigate how convective aggregation responds to changes in mean convection lifetime and mean boundary-layer MSE under warming. The parameter sensitivity experiments confirm the robustness of the results and provide insight into phase transitions across different parameter regimes. The model is expected to serve as a theoretical tool for investigating the impact of various physical processes on convective aggregation and may potentially serve as a prototype for convection parameterization that incorporates cold pools and convective organization.