The Characteristics Investigation of Ground-Based GPS/PWV During the "7.21" Extreme Rainfall Event in Beijing

GPS/PWV data, combined with automatic station data in Beijing on 20-22 July 2012, the four partitions are analyzed, and the k-means clustering method is employed. The contract results of precipitation characteristics on the basis of four partitions show that ( 1) the trend of 1 h PWV has the almost same phase, during the rising and falling process corresponding to the start and end of precipitation. ( 2) The 1 hourly variable PWV is neither increase nor decrease before the precipitation, but 3 hourly variable PWV rises can reach more than 10 mm. The 3 hourly variable PWV is better indication of the intensity of rainfall and the precipitation area, with 3-5 h forecast precipitation for the warning instructions in the practice of forecasting. ( 3) The PWV of spatial distribution is consistent to the characteristics of precipitation movement from southwest to northeast and gradually increase, and precipitation has a maximum value in 3-4 h before precipitation starts. It has the certain significant instruction to predict future precipitation area and precipitation distribution in practice of forecasting.