14 Years of GPS Tropospheric Delays in the French-Italian Border Region: A Data Base for Meteorological and Climatological Analyses

Abstract

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.

A review of the remote sensing of lower tropospheric thermodynamic profiles and its indispensable role for the understanding and the simulation of water and energy cycles

“…For this reason ZTD data are becoming increasingly useful for weather and climate research [ Wickert and Gendt , ]. The tropospheric WV estimates retrieved from GNSS postprocessed data are used not only for the analysis of meteorologically significant events [ Bock et al ., ; Walpersdorf et al ., ; Brenot et al ., ; Van Baelen et al ., ; Labbouz et al ., ] and for process‐oriented studies [ Adams et al ., ] but also for the evaluation of long time series with an homogeneous analysis scheme in the framework of climate studies [ Wang et al ., ; Sguerso et al ., ]. Higher resolution observations of the WV distribution in the lower troposphere may be realized using STDs.…”

2D PWV monitoring of a wide and orographically complex area with a low dense GNSS network

“…The ZTD can be computed in the zenith direction above the GNSS station using an appropriate mapping function. The estimation of the ZTD helps to enhance the positioning precision and interpret severe meteorological events, as demonstrated in previous studies (Bouma and Stoew 2001;De Pondeca and Zou 2001;Basili et al 2003;Bock et al 2008;Boniface et al 2009;Bennitt and Jupp 2012;Sguerso et al 2013Sguerso et al , 2015Tsuda et al 2013).…”

“…An element of innovation in this field has been introduced by Sguerso et al (2013) who proposed the use of several existing regional, national, and international GNSS PSs to estimate the ZTD for climatological applications and to monitor the PWV content of a wide and orographically complex area.…”

“…The ZTDs and gradients were calculated for each PS in the network, simultaneously with a daily positioning solution for 24-h sessions. The following settings were implemented (see Sguerso et al 2013, for more details):…”

“…The ZTD estimates were validated using two different strategies: internal and external comparisons (see Sguerso et al 2013, for further details).…”