A Single Tropical Rainbelt in Global Storm-Resolving Models: The Role of Surface Heat Fluxes Over the Warm Pool

Abstract

Global uncoupled storm-resolving simulations using the ICOsahedral Non-hydrostatic (ICON) model with prescribed sea surface temperature (SST) show a double band of precipitation in the Western Pacific, a feature explained by reduced precipitation over the warm pool. Three hypotheses using an energetic framework are advanced to explain the warm pool precipitation bias, and they are related to (a) high-cloud radiative effect, (b) too-frequent bottom-heavy circulation or highly efficient precipitating shallow convection, and (c) surface heat fluxes in light near-surface winds. Our results show that increasing surface heat fluxes in light near-surface winds produces more precipitation over the warm pool and a single precipitation band in the Western Pacific. This change increases precipitation over the Indo-Pacific region, and intensifies the circulation in the tropical Pacific, with more frequent and intense top-heavy circulation over the warm pool. Simulations with an increased high-cloud radiative effect do not affect precipitation over the warm pool. According to the energetic framework, this is due to compensation between the radiative effect and both, surface heat fluxes and circulation. Moreover, the representation of shallow convection does not affect warm pool precipitation. Thus, our results show the importance of the feedback between winds, surface heat fluxes, and convection for getting a single oceanic tropical rainbelt in regions of weak SST gradient as the warm pool.