持续性强降水的区域模式动力中期预报研究

A study of the regional model medium-term dynamic forecasting of persistent severe rainfall

持续性强降水及其次生灾害给人民的生产和生活造成严重影响,延伸其模式动力预报能力对防灾、减灾具有重要意义。随着对持续性强降水过程形成机理及模式动力中期预报认识的不断提高,以减小模式初始条件误差、边界条件误差以及内场预报误差为目标提出了一系列动力中期预报技术方法,主要包括:针对边界条件提出低通滤波技术方案,改进了5 d以上的环流及降水预报;针对模式预报内场进行谱逼近技术试验,对提前3—7 d的小雨以上量级的降水预报改进明显;针对初始条件进行多尺度混合更新初值技术预报试验,融合全球预报的大尺度场及区域模式预报的中小尺度场进行15 d预报,明显提高了50及100 mm以上的持续性累积降水预报时效。

Persistent severe rainfall(PSR)and its related phenomena lead to considerable threats to human safety and economic stability.Thereby,prolonging the forecast range would be of great importance to enhance our disaster prevention and mitigation capabilities.With in-depth understanding of the formation mechanisms for PSR events and the medium-term dynamic forecast methodology in the regional model,a set of improved methods for the medium-term dynamic forecasting of PSP events using the regional Weather Research and Forecasting(WRF)model is summarized with the aim to reduce errors in initial condition,lateral boundary condition and regional model interior forecasting.For the lateral boundary condition,the low-pass filtering method is applied to enable better forecasting of circulation fields and precipitation at lead times above 5 days.For the regional model interior forecasting,the use of spectral nudging leads to obvious improvements in the forecast of precipitation in the categories above light rain at lead times of 3-7 days.For the initial condition,the update of initial condition is an effective method to retain the large-scale forecast of the global model prediction and the small-scale features of the WRF forecasts.Results of 15-day forecasts using the WRF indicate that the update of initial condition significantly improve the forecast of accumulative precipitation above 50 and 100 mm.