Evaluation of a regional spectral model for the East Asian monsoon case studies for July 1987 and 1988

This study examines the National Centers for Environmental Prediction Regional Spectral Model (NCEP RSM)'s capability as a tool for providing regional climate details over East Asia during the summertime. Toward this end, perfect boundary condition experiments driven by analysis data are performed. The NCEP-National Center for Atmospheric Research (NCAR) re-analysis is used to provide large-scale forcings for the RSM configured with an approximately 25-km grid over East Asia centered on the Korean peninsula. Month-long simulations are conducted for July, which is the major monsoon precipitation period for Korea. The selected years are 1987 and 1988, which correspond to an El Nino and La Nina year, respectively. Overall, the model results are satisfactory in terms of the simulated large-scale features for the different years. Deviation of the simulated large-scale features from the analysis generally remains small. Domain averaged error of the simulated temperature shows a maximum of 0.8K at 300 hPa, and relative humidity less than 2 % within the entire troposphere. A discernible bias is found in the simulated climate, including a warming in the northern part and a cooling in the southern part of the domain in the lower troposphere. Cooling is dominant in the middle and upper troposphere, with values less than 1K in much of the domain. This deviation commonly appears for both years, indicating that the anomaly forecasts relative to a RSM climatology can alleviate uncertainties related to a RSM systematic error. The monthly accumulated precipitation simulated by the RSM compares well with the observations in terms of anomalous precipitation patterns for the two different summers. Regional features, including a local maximum and minimum, are not reproduced well in the RSM. However, the amount of the domain-averaged precipitation for a month is nearly the same as that recorded by observations. The skill of providing the daily variation of simulated precipitation over Korea is relatively poor. Evolution of the daily precipitation in the simulations generally compares with the observations qualitatively, but the amount and onset of precipitation events are not well reproduced. The two severe weather events causing disastrous rainfall over Korea, a tropical cyclone and a mesoscale convective system, are evaluated in detail.