Evaluating Precipitation Enhancement Associated with Convective Mergers in the Global Storm-resolving Models of DYAMOND Summer Phase

Abstract

This study is the first to quantify the precipitation enhancement associated with the merging of mesoscale convective systems in the tropics and to evaluate global storm-resolving models (GSRMs). By classifying events into non-merger single-cell and merger multi-cell convection, we analyze how systems evolve during the DYAMOND Summer Phase in the tropics and subtropics. Both observations and models show that these two storm types form where column water vapor exceeds 50 mm, particularly across Asia and the Intertropical Convergence Zone. While most models capture the spatial distribution of non-merger systems in association with the simulated moisture biases, discrepancies in merger systems, which occur mainly near coastal regions, are more significant and highly variable among models. Observed merger systems are 2.1-2.4 times more intense in maximum rainfall and last longer (> 20 hours) than non-mergers. However, models show a larger spread in enhanced intensity and in the timing of peak rainfall in merger systems. These results underscore the importance of accurately representing both large-scale moisture and convective processes in GSRMs.