14 years of GPS tropospheric delays in the French–Italian border region: comparisons and first application in a case study

Global Positioning System (GPS) data from 181 permanent stations extracted from different networks covering France and the Italian part of the Alps are used to estimate a homogeneous set of tropospheric parameters over 14 years (from January 1998 to May 2012). The tropospheric Zenith Total Delay (ZTD) quantified in the GPS data analysis is closely related to the value of integrated water vapor above each GPS station. GPS ZTD is already successfully used for operational weather prediction and meteorological analyses, providing valuable data to improve our comprehension of the tropospheric water cycle and in particular to improve the prediction of precipitations. Moreover, GPS tropospheric measurements are intrinsically stable, so that long-term observations represent a signi``ficant contribution to climatological studies. The results of a homogeneous reanalysis of up to 14 years of data with MIT’s GAMIT/GLOBK software are presented. The estimated tropospheric parameters are one ZTD every 2 h and one couple of horizontal tropospheric gradients, seven times a day for each station, simultaneously with a daily positioning solution. A quality check of the tropospheric parameter time series identifies offsets, for example, due to instrument changes at individual sites. Our analysis strategy using the empirical GMF is validated by a comparison with the new GPT2 model. Moreover, a comparison with the IGS analysis of 1 year is provided for common stations. The resulting verified time series can be used for meteorological and climatological studies. As first examples, we present a convergence test for the ZTD change in time and a regional climatological approach that could permit identifying specific patterns of ZTD variation that are related to severe weather events. The 181 ZTD and gradient time series are made available in the Reseau National GPS permanent (RENAG) database.