Precipitation on the Manus Island of Papua New Guinea and ice cloud radiative effects in the surrounding atmosphere in boreal winters

Abstract The longwave cloud radiative effect (LW CRE) plays a critical role in regulating tropical moist convection by modifying the atmospheric energy budget. While previous studies have linked LW CRE to the maintenance of convective quasi-equilibrium (CQE) on large scales, its influence at shorter timescales and on individual convective events remains less explored. In this study, we analyze the relationship between precipitation and LW CRE on daily timescales at a location over the equatorial western Pacific. We focus on how LW CRE shapes the thermodynamic environment prior to deep convection. The present results show that enhanced LW CRE and planetary boundary layer (PBL) moisture increase column-integrated moist static energy (MSE) before heavier rainfall events, creating conditions more favorable for deep convection. Notably, LW absorption at the cloud base heats the lower portion of cirrus clouds and the radiative heating enhances the mid-to-upper tropospheric MSE. In addition, increased humidity in the lower free troposphere above the PBL is found to increase the height of anvil cloud tops through minimizing buoyancy reduction during the mixing of rising plumes/parcels with the ambient environment. These findings contribute to a process-level perspective on how LW CRE shapes tropical moist convection.