Getting a single tropical rainbelt in a global storm-resolving model

Resolving deep convection using a horizontal grid spacing of 10 km or finer was supposed to produce a correct representation of tropical precipitation. Global coupled or uncoupled storm-resolving simulations using the ICOsahedral Non-hydrostatic model (ICON) show a proper representation of the tropical rainbelt over land. However, the tropical rainbelt over the western Pacific shows a double structure, and the uncoupled simulation relates this bias to the lack of precipitation over the warm pool. We test three hypotheses based on an energetic framework to explain the lack of precipitation over the warm pool, 1) the radiative effect of high clouds, 2) too-frequent or efficient shallow precipitating clouds, and 3) surface heat fluxes in light near-surface winds. Experiments show that in ICON, increasing surface heat fluxes over light near-surface winds produces more precipitation over the warm pool, giving a single tropical rainbelt over the Western Pacific. An increased radiative effect of high clouds did not increase warm pool precipitation due to compensation with reduced surface heat fluxes and changes in circulation. Moreover, the representation of precipitating shallow convection does not affect warm pool precipitation. Thus, our experiments indicate the role of surface heat fluxes in light near-surface winds to trigger precipitation, as over the warm pool.