The surface rainfall processes and diurnal variations associated with tropical oceanic convection are examined by analyzing a surface rainfall equation and thermal budget based on hourly zonal-mean data from a series of two-dimensional cloud-resolving simulations.The model is integrated for 21 days with imposed large-scale vertical velocity,zonal wind,and horizontal advection obtained from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) in the control experiment.Diurnal analysis shows that the infrared radiative cooling after sunset,as well as the advective cooling associated with imposed large-scale ascending motion,destabilize the atmosphere and release convective available potential energy to energize nocturnal convective development.Substantial local atmospheric drying is associated with the nocturnal rainfall peak in early morning,which is a result of the large condensation and deposition rates in the vapor budget.Sensitivity experiments show that diurnal variations of radiation and large-scale forcing can produce a nocturnal rainfall peak through infrared and advective cooling,respectively.