Abstract
A global, 2-hourly atmospheric precipitable water (PW) dataset is produced from ground-based GPS measurements of zenith tropospheric delay (ZTD) using the International Global Navigation Satellite Systems (GNSS) Service (IGS) tropospheric products (~80–370 stations, 1997–2006) and US SuomiNet product (169 stations, 2003–2006). The climate applications of the GPS PW dataset are highlighted in this study. Firstly, the GPS PW dataset is used as a reference to validate radiosonde and atmospheric reanalysis data. Three types of systematic errors in global radiosonde PW data are quantified based on comparisons with the GPS PW data, including measurement biases for each of the fourteen radiosonde types along with their characteristics, long-term temporal inhomogeneity and diurnal sampling errors of once and twice daily radiosonde data. The comparisons between the GPS PW data and three reanalysis products, namely the NCEP-NCAR (NNR), ECMWF 40-year (ERA-40) and Japanese reanalyses (JRA), show that the elevation difference between the reanalysis grid box and the GPS station is the primary cause of the PW difference. Secondly, the PW diurnal variations are documented using the 2-hourly GPS PW dataset. The PW diurnal cycle has an annual-mean, peak-to-peak amplitude of 0.66, 0.53 and 1.11 mm for the globe, Northern Hemisphere, and Southern Hemisphere, respectively, with the time of the peak ranging from noon to late evening depending on the season and region. Preliminary analyses suggest that the PW diurnal cycle in Europe is poorly represented in the NNR and JRA products. Several recommendations are made for future improvements of IGS products for climate applications.
Highlights
Permanent Global Positioning System (GPS) stations in Irkutsk, IRKT and IRKM, are the base stations in the Baikal geodynamic net‐ work
GPS measurements can be useful for continuous remote sensing of the atmo‐ sphere
In formula (7), only the atmospheric pressure should be taken into account, which greatly simplifies the calcu‐ lations of ZWD from GPS measurements by subtracting ZHD from zenith tropospheric delay (ZTD)
Summary
Permanent GPS stations in Irkutsk, IRKT and IRKM, are the base stations in the Baikal geodynamic net‐ work. In addition to the geodynamic parameters of crustal movements and deformations, the total tropospheric zenith delay data was collected. The zenith tropospheric delay (ZTD) is one of the most significant corrections [Davis et al, 1985] in high‐ precision geodetic calculations from GPS measure‐ ments [Lukhnev et al, 2013; Dembelov et al, 2015]. The emerging denser GPS networks, estab‐ lished mainly for studies of geodynamics [Sankov et al, 2014] and the ionosphere, offer the possibility of using GPS data for efficient weather forecasting [Dembelov et al, 2015]. GPS site (IRKM) is located on a distance of 6 km from the Irkutsk meteorological station (WMO ID: 30710) and 43 km from the Angarsk meteorological station (WMO ID: 30715). The error of vertical meteo‐ rological data records in Angarsk for IRKM station does not exceed 5 %
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