地基GPS水汽资料在北京“7·10”暴雨过程研究中的应用

Application of the Ground-based GPS/PW Data to Investigate the "7·10" Heavy Rainfall Event in Beijing

利用2004年7月9-11日北京房山地基GPS探测网逐30分钟柱积分水汽总量(PW,Precipitable Water Vapor)资料,通过分析和数值模拟研究了北京2004年7月10日暴雨天气过程。观测分析表明:地基GPS测站上空水汽总量值的时间变化趋势对暴雨的发生、发展以及过程降水量的分析和预报有一定指示意义。利用NCEP全球预报系统GSF分析场资料作为背景场,采用12/4km双向两层嵌套WRF模式及其三维变分系统,通过同化7月9日1200 UTC地基GPS水汽总量等观测资料进行了36小时数值对比试验。数值研究表明:地基GPS水汽总量数据资料的初值同化明显增强模式初始场湿度,明显提高模式对该暴雨过程降水时段、落区和强度的预报水平。

The precipitable water vapor （PW） data at 30-min intervals are analyzed and assimilat- ed into the WRF model for the “7·10” Beijing heavy rainfall event that occurred in the period of 9-11 July, 2004. Observational results show that the temporal variation of the GPS/PW is an in- structive factor for the analysis and prediction of this heavy rainfall event. Using the WRF modeland its 3D-Var system with two-way and two-nested grids of 12/4km, three 36h numerical ex- periments are conducted to investigate the impacts of PW with the variation analyses at 1200 UTC of July 9 as the initial fields. Numerical experimental results show that the assimilation of GPS/ PW observations significantly helps to improve the moisture analysis at the initial time, then helps to improve forecasts of the location, intensity and evolution of this heavy rainfall event.