针对对流降水预报的BJ-RUC系统1小时更新循环方案研究

THE DESIGN OF HOURLY UPDATE BJ-RUC SYSTEM FOR IMPROVING CONVECTIVE PRECIPITATION FORECASTING

为了提高快速更新循环系统的分析和预报水平,在BJ-RUC系统中,发展了针对1小时更新循环的分步同化方案。分步同化的方案有效解决了在现有变分同化系统中如何在分析场中加入更多的对流尺度观测信息,同时保持大尺度背景场平衡的问题。该方案是将大尺度的常规观测和小尺度、高分辨率的观测资料分步同化,从不同尺度的观测中分别提取出大尺度和对流尺度的信息。以2009年北京地区夏季的4次强降水过程为个例进行同化和预报试验。结果表明,该方案在12小时的预报时效内能有效提高降水预报。对飑线个例的详细分析结果显示,分步同化方案可以使分析场中同时保留大尺度和对流尺度的信息,从而使预报的降水位置和强度等方面都更准确,降水预报评分有明显提高。

This study shows an improved version of Beijing Rapid Updated Cycling（BJ-RUC） forecast system with hourly update frequency and its impact on quantitative precipitation forecast（QPF）. The new BJ-RUC system adopted the two-step assimilation strategy with additional improvements. Synoptic and convective observations are assimilated in different steps to extract both large-scale and convective-scale information from observations. The new system was tested with four convective cases in Beijing area during summer 2009. A detailed analysis on how the new system impacts on convective-scale QPF was conducted using a squall line case in Beijing area on 23 July 2009. The improvement in the new system results in improved QPF throughout most of the 12 h forecast period. The diagnoses of the analysis fields show that the new system is able to preserve key convective-scale as well as large-scale structures that are consistent with the development of the weather system. This study provides a prototype for operational short-term prediction of the local convective weather system.