A modeling study of diurnal rainfall variations during the 21-day period of TOGA COARE

The surface rainfall processes and diurnal variations associated with tropical oceanic convection areexamined by analyzing a surface rainfall equation and thermal budget based on hourly zonal-mean data from a seriesof two-dimensional cloud-resolving simulations. The model is integrated for 21 days with imposed large-scale verticalvelocity, zonal wind, and horizontal advection obtained from the Tropical Ocean Global Atmosphere CoupledOcean-Atmosphere Response Experiment (TOGA COARE) in the control experiment. Diurnal analysis shows that theinfrared radiative cooling after sunset, as well as the advective cooling associated with imposed large-scaleascending motion, destabilize the atmosphere and release convective available potential energy to energizenocturnal convective development. Substantial local atmospheric drying is associated with the nocturnal rainfallpeak 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 anocturnal rainfall peak through infrared and advective cooling, respectively.