Application Analysis On GPS Precipitable Water Wapor In Weather Forecast At Xi'an Region

Water vapor plays an important role on weather and climate,especially when heavy rains and strong convective weather occur.The water vapor observation data obtained by solving the basic data of GPS(Global Positioning System)is a powerful supplement to the conventional water vapor observation data.The application of GPS water vapor data to the study of numerical models can further deepen the understanding of the mechanism of precipitation change which is of great significance for improving the prediction.This paper analyzes several precipitation weather processes in Xi'an by using ground-based GPS water vapor data in Xi'an,and summarizes the statistical relationship between GPS precipitation and observed precipitation,and analyzes the seasonal characteristics of GPS precipitation data in Xi'an.On this basis,GPS water vapor data are introduced into the initial field of WRF model by using WRFDA assimilation system.The numerical simulation test was carried out on the precipitation process occurring in Xi'an from July 28 to August 1,2011.The main conclusions are as follows:(1)By comparing the quality of atmospheric water vapor data and GPS water vapor data,it is found that the two data show good consistency,which indicates that GPS water vapor observation data can be effective supplement for studying and analyzing conventional sounding data in rainstorm mesoscale system.Comparing PPP with double-difference method by using water vapor data of Lintong Station,it is found that the PPP method has poor stability compared with the double difference method,and there is a problem of large calculation variation.The stability of measured data can not meet the relevant requirements of weather forecasting application,so the double difference method is better and more suitable for the calculation of GPS water vapor data.(2)Through the calculation of water vapor content data during the two weather processes of Xi'an Station on August 2-3,2013 and August 17-18,2015,it studies and analyzes the correlation characteristics between GPS water vapor content,air relative humidity change and precipitation.(3)Through the analysis of the variation characteristics of GPS/PWV in different seasonal precipitation processes at Eyi Station,the GPS/PWV maintains relatively stable inspring and winter,and its growth period can be seen before precipitation with longer duration.Summer precipitation is changing rapidly,and generally does not accumulate water vapor for a long time before precipitation occurs.Especially in the case of short-term heavy precipitation,it is generally larger than the mean value.Because it does not exceed the mean value so much,it is not considered to have a more significant indication in summer.(4)Taking the regional rainstorm weather process in Shaanxi Province from July 28 to August 1,2011 as an example,the NCEP Global System of Forecasting is used to analyze the field data as the background to assimilate and classify the total water vapor observation data of 7 ground-based GPS stations in Xi'an and 1200 UTC on July 30 by WRF three-dimensional system.It is found that with the assimilation of GPS water vapor data into the model,the initial humidity field and the prediction of the model can be improved to a certain extent,and it can be one of the ways to improve the performance of local numerical model prediction in Xi'an.