Abstract:
This study investigates the simulation skill of Meiyu precipitation over the middle and lower reaches of the Yangtze River (MLYR) using the regional climate model RegCM4.7. To examine the potential effects of cumulus convective parameterization schemes (CCPSs), horizontal resolutions (HRs), microphysics parameterizations, and land models on the simulation skill of Meiyu precipitation, we conducted 96 sets of numerical experiments based on various model configurations. In general, RegCM4.7 demonstrates good performance in simulating Meiyu precipitation over the MLYR from the perspectives of the Meiyu simulation experiments for the super Meiyu case in summer 2020 and the long-term period of 1990–2020. Our quantitative analysis reveals that CCPSs play a vital role in influencing the Meiyu simulation skill. Specifically, the Tiedtke scheme shows the best performance in simulating Meiyu precipitation, whereas the Grell scheme shows relatively low skill. The relatively reasonable simulation achieved using the Tiedtke scheme was attributed to its effective representation of convective precipitation, as well as the ratio of convective precipitation to stratiform precipitation. Furthermore, the impacts of HRs on Meiyu precipitation simulation are closely linked to the terrain. The low-HR (60 km) experiment tends to show a considerable overestimation of precipitation over regions with complex terrain. Along with the increase in HR, such wet bias of precipitation due to complex terrain can be considerably reduced. It is found that the mesoscale convective system (MCS) precipitation is anchored by steep terrain in the low-HR experiment, leading to a wet bias in the long-term average of precipitation. By contrast, the high-HR experiment replicates the diurnal variation of MCSs over the complex terrain that is generated in the afternoon and gradually propagates eastward. Such a reasonable representation of MCS features contributes to the reasonable estimation of long-term average precipitation patterns for the Meiyu season. Besides, results show that the Meiyu simulation skills are not sensitive to the choice of microphysics parameterizations and land models. Overall, the current numerical experiments show that RegCM4.7 is capable of simulating Meiyu precipitation over the MLYR (even for the super Meiyu case in 2020) and that the Tiedtke CCPS configuration generally exhibits higher simulation skills than other CCPSs in RegCM4.7.