Improving the diurnal cycle simulation of land precipitation using a revised NSAS convective scheme in a global non-hydrostatic model

In a relatively coarse resolution atmospheric model, cumulus convective parameterization helps to solve the problem of insufficient precipitation simulation, and also to ameliorate the simulation of diurnal precipitation cycle, which typically displays early appearance of diurnal peak over land. In this study, the new simplified Arakawa-Schubert scheme (NSAS) with a closure of adjusting the cloud function to an observed climate sate, which is coupled in a global non-hydrostatic atmospheric model, i.e. the Yin-Yang-grid Unified Model for the Atmosphere (YUNMA), is used to investigate the impacts of convective scheme on diurnal cycle of precipitation. Two new diagnostic closures and a convective trigger function based on the tropospheric large-scale forcing are suggested, which are introduced into the NSAS scheme for comparison with the original scheme. Numerical results of the 0.25-degree model in 3-month batched real-case simulations reveal the simulated diurnal variation in close agreement with observation by using the revised NSAS convective scheme with a dynamical constraint on the initiation of convection and a tuned threshold of cloud function variation in the YUNMA model. By reducing the occurrence of convection during peak solar radiation hours, the revised scheme is demonstrated to be effective in delaying the appearance of early-afternoon rainfall peaks over most land areas and in accentuating the nocturnal peaks that are wrongly concealed by the stronger afternoon peaks. In addition, the revised scheme enhances the simulation capability of the precipitation probability density distribution, such as increasing the extremely low- and high-rainfall-rate events and decreasing small and moderate rainfall-rate events, which contributes to the precipitation bias reducing over mid-latitude and tropical lands.