14 YEARS OF GPS TROPOSPHERIC DELAYS IN THE FRENCH-ITALIAN BORDER REGION: A DATA BASE FOR METEOROLOGICAL AND CLIMATOLOGICAL ANALYSES

Abstract. 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 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 significant contribution to climatological studies.

The results of a homogeneous reanalysis of up to 14 years of data with MIT's GAMIT/GLOBK software version 10.4 are presented. The estimated tropospheric parameters are 1 ZTD every 2 hours and one couple of horizontal tropospheric gradients (NS and EW) every 3 hours for each of the 181 stations, 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.

The resulting verified time series can further be used for meteorological and climatological studies that go beyond the geodetic work presented here. Thanks to the length of the data set in time, a regional climatological approach could permit identifying specific patterns of ZTD variation that are related to severe weather events. The regional GPS stations could then contribute to an early warning system.