Research On Precipitable Water Vapor Retrieval And Typhoon Monitoring In Chongming Based On GNSS

Chongming District is located at the mouth of the Yangtze River,with superior geographical location and ecological environment,and occupies an irreplaceable position in the development of Shanghai and even the Yangtze River Economic Belt.In recent years,with the abnormal global climate change,Chongming District is facing increasing risks of various weather disasters.Typhoon is one of the most frequent and harmful extreme weather disasters in this region.Precipitable Water Vapor(PWV)is an important indicator for the monitoring of extreme weather,such as typhoon.Ground-based Global Navigation Satellite System(GNSS)can be used to retrieve Precipitable Water Vapor(GNSS/PWV).Compared with traditional detection methods,GNSS/PWV has the following advantages,such as high precision,high temporal and spatial resolution,low cost.Under the above background,the PWV data of Chongming area in 2019-2020 were retrieved based on the observation data of The Continuous Operation Reference System(CORS),and the temporal and spatial variation characteristics of PWV during typhoon were analyzed.It aims to use GNSS/PWV to monitor typhoon disasters and provide basic data support for regional disaster prevention and mitigation policies:(1)Based on the analysis of the periodic characteristics of atmospheric weighted average temperature(T_m)of sounding station,an empirical T_m model based on Fourier series for Chongming region is constructed.Compared with GPT2w model,the model complexity is reduced and the root mean square error is reduced by 7.0%.Pearson correlation coefficient method was used to confirm that there was a significant positive correlation between and.Based on this,annual model and seasonal model based on meteorological parameters were constructed in Chongming region.After accuracy test,the average deviation of annual model in Chongming region was reduced by 18.9%and the root mean square error was reduced by 14.8%compared with Bevis model.At the same time,the seasonal model in summer and winter can further improve the calculation accuracy of T_m,and the winter model has a great improvement.(2)The temporal and spatial variation characteristics of atmospheric precipitable water vapor and meteorological elements(temperature,pressure,rainfall)during several typhoons were analyzed.The results of time series analysis verify the rainfall process of typhoons:before the typhoon approaches,the temperature rises,and liquid water on the ground usually turns into gaseous water.At this time,PWV rises,and the pressure drops.When typhoon approaches,PWV reaches a certain value,the temperature drops,and a large amount of water vapor gathers and condenses into water,forming rainfall.When the typhoon is far away,the PWV rapidly decreases,not enough to form rain,temperature,pressure began to rise.The results of PWV spatial characteristics analysis show that the PWV spatial variation is consistent with the path of typhoon:the closer the area is to typhoon,the more obvious the PWV variation is;PWV will change first in the area where typhoon approaches first.(3)Based on PWV and rainfall data of NYZX station in Chongming Continuous Operation monitoring system from 2019 to 2020,a rainfall forecast model with seven different combinations of factors was constructed using PWV maximum,PWV increase and PWV increase rate as the predictors.The optimal thresholds of each predictor were selected by critical success index(CSI)score method.Combined with POD and FAR,the three-factor combined model was determined to be the optimal threshold-based rainfall prediction model.The hit ratio of typhoon rainfall predicted by the model was higher than 70%and the false positive rate was lower than 25%.