Characteristics of Precipitable Water Vapor of Summer Rainstorm Based on Beijing GPS-MET Network

Based on the inversion data of perceptible water vapor (PWV) from ground-based GPS network in Beijing, the ichnography distribution characteristics of PWV before precipitation are analyzed. Using ground and upper air meteorological data from the routine AWS and IAWS, the specific humidity of different heights are calculated, which are associated with temperature and wind, the large scale vapor transportation and the local mesoscale convergence. The changes of PWV, occurrence time of precipitation, rainfall and hourly rain intensity are analyzed.According to the precipitation and the curve of PWV in July 2009, the rainfall are not correspond with the PWV value, but it is nearly associated with the vapor transportation and vapor convergence evoked by all kind scales weather systems.The value of PWV increases continuously before precipitation, sometimes there is a sudden increase an hour before precipitation. The ichnography distributions of high PWV value are accord with precipitation area.Curve change of PWV is nearly related with vapor transportation and convergence, and the PWV is related with vapor resource in 3 ways. There is large scale vapor transportation and local mesoscale convergence, the PWV is stably increasing, 4 hours before precipitation, the PWV rises sharply, the local precipitation will occur 2—3 hours after the value of PWV reaches above 50 mm. There is large scale vapor transportation, but there is not precipitation mechanism, the PWV has exceeded 50 mm, the vapor will increase continuously and maintain. The rain will not occur until the precipitation mechanism appears. There is no apparent resource of outer vapor, and the overall level of the PWV is not high. Effects of local apparent wind converge and shear, 2 hours before precipitation, the PWV value increases sharply. The PWV value will exceed 50 mm an hour before precipitation, and the precipitation area is relative convergence. Above all, it shows that if vapor conditions and precipitation mechanisms are suitable, the precipitation will occur 2—3 hours after PWV reaches 50 mm. Otherwise it will not rain even if the PWV value is greater than 50 mm until precipitation mechanism occurs. From the curve of PWV and timely change of precipitation, 4 hours before precipitation, the curve of PWV shows abrupt increase by larger than 1.1 mm per hour. The maximum of hourly rain intensity occurs 1—2 hours after the peak of PWV.