Simulation of the 18-d summer heavy rainfall over East Asia using a regional climate model

Abstract

In this study, an 18-d-long heavy-rainfall event that occurred over the Korean Peninsula in August 1998 was simulated by using the Seoul National University Regional Climate Model (SNURCM) with horizontal resolution of 20 km. In order to determine the potential predictability and the capability of the RCM in the simulation of long-lasting, extremely heavy rainfall, a time-lagged ensemble with five different initial conditions of one-day intervals, and two daily forecast experiments with initial conditions at 00 UTC (24-h and 48-h forecasts) were performed. Further, an experiment with high horizontal resolution of 5 km was performed. The ensemble as well as individual runs simulated the evolution and time variation in the convective systems responsible for the heavy rainfall. Somewhat better patterns and magnitudes of precipitation were obtained for the ensemble as compared to those of the individual runs. The continuous integration of the 18-d heavy rainfall in the ensemble corresponded with the 24-h and 48-h forecast experiments that employed the initial data obtained every day during the simulation period. Therefore in the RCM, the daily evolution of the heavy-rainfall event was reproduced by large-scale forcing. In the experiment with the 5-km horizontal resolution, the amount and intensity of heavy precipitation and its diurnal variation were better reproduced by the combined effects of increased horizontal resolution and topography.