GNSS PWV Estimation Over China From Ground-based GNSS And ECMWF Data

Water vapor is an important part of the earth's hydrosphere,and its content and distribution change are important factors in the formation and evolution of extreme catastrophic weather.Accurate measurement of water vapor and its distribution change is one of the basic problems in weather forecast and climate research.The Global Navigation Satellite System(GNSS)plays an important role in retrieving high temporal–spatial resolution precipitable water vapor(PWV)due to its high spatial and temporal resolution and low cost.The weighted mean temperature(Tm)is a key parameter for the GNSS PWV estimation,which acts as the conversion factor from the zenith wet delay(ZWD)to the PWV.The Tm is determined by the air pressure and water vapor pressure,while it is not available nearby most GNSS stations.The empirical formular is often applied for the GNSS station surface temperature(Ts)but has a lower accuracy.The main research contents of this paper are as follows:(1)In this paper,the temporal and spatial distribution characteristics of the coefficients of the linear Tm-Ts model are analyzed,and then,a piecewise-linear Tm-Ts relationship is established for each GPS station.The Tm accuracy was increased by more than 10% and 20%for 86 and 52 radiosonde stations,respectively.The PWV time series at 377 GNSS stations were further obtained from the GPS observations and meteorological data from 2011 to 2019.The PWV accuracy was improved when compared with the Bevis model.(2)For lack of a few sites in some period of time the observed meteorological parameters,we used the ECMWF ERA5 data sets,using interpolation method to get temperature and pressure at sites,after compared with the measured data validation,we found the accuracy of temperature and pressure obtained by interpolation with this data set can meet the requirement of high precision precipitation inversion.(3)Furthermore,the daily and monthly average values,long-term trend,and its change characteristics of the PWV were analyzed using the high-precision inversion model.The results showed that the averaged PWV was higher in Central-Eastern China and Southern China and lower in Northern China.The PWV is increasing in most parts of China,while the some PWV in North China show a downward trend.The PWV sequence of GPS stations distributed in the typhoon-affected area is extracted,and the path of two typhoons is simulated.According to the position of each station and the time when the PWV of each station reaches the peak,the direction of typhoons and the change of the direction can be calculated.