bbGPS/PWV资料三维变分同化改进MM5降水预报连续试验的评估

利用区域地基GPS网反演的高时空密度的大气垂直方向水汽总量，也称为可降水量（PWV），可大大弥补常规探空探测水汽资料的不足。为了全面评估区域GPS网PWV资料同化对业务数值天气预报改进程度的目的，在个例研究分析的基础上，进行了连续38天的GPS/PWV资料三维同化（3D-Var）改进数值业务预报的试验。研究方法是根据长江三角洲地区GPS气象网在2002年梅雨和盛夏季节观测的刖资料，通过三维变分同化建立中尺度数值预报模式MM5的初始场，逐日作出长江三角洲地区24小时的降水量预报。以6小时累积雨量为对象，与未同化GPS／刖资料的MM5的相应预报比较，通过多种评分方法，评估了GPS／PWV资料改进MM5降水预报的效果。结果表明GPS／PWV资料同化后的MM5降水预报能力在大部分时间和大部分地区都有所提高，主要是伪击率有较明显的下降，对小范围降水预报的改进更为明显。预报明显改进的区域恰好位于GPS站填补常规探空站间距较大的地区。

Evaluation of the Continuous Experiment of 3-Dimentional Variation Assimilation of GPS/PWV Data into MM5 Model to Improve the Precipitation Forecasts

The vertical integrated atmospheric moisture, or the precipitable water vapor (PWV) with high temporal and spatial resolution retrieved from a ground-based GPS network can supply the gap of the conventional radiosoundings. In order to evaluate the improvement of the GPS/PWV data assimilating to operational numerical forecasts, a continuous experiment of 3-dimentional variation assimilation (3D-Var) of GPS/PWV data into MM5 model is conducted. Through the 3D-Var assimilation of GPS/PWV data, the initial field of MM5 model is built at 20:00 every day, and the hourly rainfalls over the Yangtze River Delta area are forecasted for 24 hours. Comparing with the forecasted 6 hour's accumulative rainfalls without GPS/PWV data assimilation,the improvement effects of the MM5 precipitation forecasts with GPS/PWV data assimilation are evaluated by several test methods. The results show that the MM5 precipitation forecasts with GPS/PWV data assimilation are totally improved in the most days and most stations, especially in the days with smaller area of precipitation. The improvement of precipitation forecast mainly attributes to the significant decrease of the percent of false detection. The areas where the precipitation forecasts are improved significantly coincide in the area with sparser regular radiosounding data.