Diurnal variations of simulated precipitation over East Asia in two regional climate models

The diurnal variations of precipitation over East Asia simulated by the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) and the Weather Research and Forecasting (WRF) model are evaluated during the integration period of June-July-August (JJA) 2006. The models reproduce the observed seasonal mean of large-scale features and precipitation satisfactorily, although the bias patterns differ in both models. The lower tropospheric circulation features are better reproduced by the WRF, while the upper-level circulations closely follow the RSM analysis. Furthermore, the RSM simulated seasonal precipitation is distinctly overestimated over land, whereas the oceanic precipitation is exaggerated by the WRF. However, the characteristics of the diurnal cycle of precipitation simulated by the two models are very similar in many aspects. Both models reproduce an afternoon peak over land and a daybreak peak over oceans. The simulated diurnal and semidiurnal cycles of precipitation amount are also comparable to the corresponding observations. However, the peaks are shifted approximately 2 h ahead. The diurnal variation of the frequency is fairly well simulated, although the semidiurnal variations are poorly resolved. The diurnal and semidiurnal variations of the intensity are not captured by either model. The ensemble mean of the model results does not provide a distinct advantage in appraising the diurnal variation of precipitation. Further physics sensitivity experiments reveal that the cumulus parameterization process influences the modulation of the simulated phase at maximum precipitation over land, whereas the amplitude is more highly controlled by the boundary layer processes.