| Atmospheric water vapor plays an important role in the occurrence and development of extreme weather.Atmospheric water vapor is the main material basis for the formation of clouds and precipitation,and its phase change and migration can significantly change the atmospheric energy distribution,affect the balance of atmospheric energy system,and provide necessary dynamic conditions for the generation and evolution of extreme precipitation events.It is of great scientific and practical significance to obtain long time series,high precision and high time resolution atmospheric water vapor information for exploring the formation mechanism of extreme precipitation weather and realizing short imminent warning and forecast.With the development and improvement of the new-generation Global Navigation Satellite Systems(GNSS),atmospheric precipitable water vapor(PWV)inversed by GNSS has been becoming a new technique for atmospheric water vapor detection.This thesis mainly focuses on the research of Ground-Based GNSS water vapor detection method and its application in heavy rainstorms.Specific research contents and conclusions are as follows:(1)Accuracy assessment of water vapor detection by four satellite systems.GAMIT/GLOBK software was used to calculate the GPS,BDS,Galileo and GLONASS observation data of MGEX station respectively for water vapor inversion,and to evaluate the accuracy of water vapor detection of different satellite systems.The experimental results show that the root mean square error(RMSE)of the zenith total delay(ZTD)of the four satellite systems is less than 13 mm when the cutoff altitude Angle set 5°.Using Radio Sounding water vapor(RS-PWV)as reference,the mean RMSE values of PWV retrieved by GPS,BDS,Galileo and GLONASS at each station were 2.25 mm,2.46 mm,2.52 mm and 2.84 mm,respectively.Compared with ERA5water vapor(ERA5-PWV),the mean RMSE values were 1.63 mm,1.86 mm,1.76 mm and 1.99 mm,respectively.The accuracy of water vapor detection by GPS was the highest,while that of BDS was lower than that of GPS and Galileo,but higher than that of GLONASS.The accuracy of water vapor detection by the four satellite systems all met the application requirements of meteorology.(2)GNSS high-precision water vapor information acquisition and long time series characteristics analysis.Crustal Movement Observation Network of China(CMONOC)tropospheric water vapor released data(GNSS-PWV1)product has certain error.For improving the accuracy of GNSS detection of water vapor,Water vapor inversion using GNSS data combined with ERA5 data(GNSS-PWV2).The accuracy improvement of GNSS-PWV2 compared with GNSS-PWV1 in different climatic regions and seasons in China was studied,and the characteristics of long time series variation of GNSS water vapor information were analyzed.The results showed that Mean Absolute Error(MAE)and RMSE ranges of GNSS-PWV2 were 1.00～2.77 mm and 1.24～3.28 mm,respectively.GNSS-PWV2 had the highest accuracy in winter,followed by spring and autumn,and the lowest in summer.GNSS-PWV2 had the best accuracy improvement in winter in temperate monsoon,temperate continental and plateau alpine climates,and RMSE increased 49.84%,63.00%and 79.43%,respectively.The subtropical monsoon and tropical monsoon climate regions showed the highest degree of improvement in spring,with 36.67%and 58.91%improvement of RMSE,respectively.The annual variation of PWV was first increased and then decreased.The annual PWV value was in the range of 0～80 mm.In the temperate monsoon,temperate continental and plateau alpine climates,the monthly PWV peak was reached in July,while in the subtropical monsoon and tropical monsoon climates,the peak was advanced to June.(3)Application of GNSS water vapor detection technology in extremely heavy rainstorm.Combining PWV retrieved from GNSS Stations in Continuously Operating Reference Stations(CORS)in Henan Province with meteorological elements such as relative humidity and total cloud cover.The temporal and spatial variation characteristics of precipitation,PWV and meteorological elements during"21?7"heavy rainstorm in Henan Province and their internal relations were analyzed.The results showed that during the heavy rainstorm,the PWV increased first with the increase of precipitation and then decreased with the decrease of precipitation.4～6 h before the peak of precipitation,the PWV rapidly increased to the extreme value,and the variation of PWV((35)PWV)ranged from+7.35 mm to+9.02 mm.When the precipitation reached the extreme value,the PWV content over GNSS station also reached the corresponding peak(above 70.58mm).The spatial distribution of PWV,relative humidity,total cloud cover and precipitation was consistented with each other.The value of PWV over central,northern and western areas of Henan Province where extreme heavy precipitation occurs was always at a high level(above 65 mm),while the content of PWV over eastern areas where no rainfall occurs was below 65 mm.The relative humidity and total cloud cover in central,western and northern Henan Province remained at the peak saturation state of 100%.The above results can provide important reference for predicting the occurrence of heavy rainstorm in the future.There are 39 figures,9 tables and 110 references in this thesis. |
