Toward a Generalized Understanding of the Role of Convective Available Potential Energy (CAPE) Removal and Entrainment Rate in Convective Parameterizations on the Diurnal Cycle of Tropical Precipitation

Abstract The diurnal rainfall cycle is a key factor affecting tropical precipitation variability. However, the diurnal cycle is not sufficiently represented in numerical models, which can be associated with convective parameterization in the models. This study presents the sensitivity of simulated precipitation over Java Island, Indonesia, to adjust two parameters in parameterization schemes. These two parameters are related to convective available potential energy (CAPE) removal and entrainment of environmental air into cumulus convection. Using a climate model, we conducted sensitivity experiments by perturbing the parameters in two plume-type convective parameterization schemes, Kain–Fritsch and Grell. Our results show a delayed phase of the diurnal cycle of the simulated precipitation over land, although this phase delay was not found over the oceanic areas. Sensitivity tests demonstrated that the phase delay of precipitation over land depends on the values of these two parameters. The timing of precipitation was improved by enhancing the degree of elimination of the vertical instability and reducing the entrainment rate. Further analyses by dividing simulated precipitation into parameterized and nonparameterized precipitation demonstrate that enhancing the degree of elimination of vertical instability can produce adequate amount of precipitation and that the reduced entrainment rate can increase the cloud top, improving precipitation timing. These results apply to both the convective parameterization schemes. Therefore, the results obtained in this study can be generalized to a range of convective parameterizations using the plume model.