Trends in the atmospheric water vapour estimated from two decades of ground-based GPS data: sensitivity to the elevation cutoff angle

Övrigt konferensbidrag, 2017

We have analysed 20 years of data from 13 GPS sites in Sweden and Finland, using two different elevation cut-off angles, 10° and 25°, to estimate the atmospheric integrated water vapour (IWV). Then we estimated the linear long-term trends of IWV which were compared to the corresponding trends from the radiosonde data at 7 nearby (< 120 km) sites and the trends given by the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA-Interim). The IWV trends given by the GPS elevation 10° and 25° solutions show similar results when compared to the trends from the radiosonde data, with correlation coefficients of 0.71 and 0.74, respectively. When compared to the IWV trends obtained from ERA-Interim, the GPS solution for the 25° elevation cutoff angle gives a significantly higher correlation (0.90) than the one obtained for the 10° solution (0.53). The results indicate that a higher elevation cutoff angle is meaningful when estimating long term trends, and that the use of different elevation cutoff angles in the GPS data processing is a valuable diagnostic tool for detection of any time varying multipath impacts.