A Comparison of Precipitable Water Vapor Estimates by an NWP Simulation and GPS Observations

Abstract

Abstract Simulated time series of the total precipitable water (PW) vapor from a limited area numerical weather prediction model are compared to estimates derived from observations done with ground-based Global Positioning System (GPS) receivers. The model data examined are from the delayed-mode High Resolution Limited Area Model (HIRLAM) data assimilation (reanalysis) and the short-range forecasts on double nested grids. The observational data are derived from GPS measurements at 25 sites in Sweden and Finland over a 4-month period, August–November 1995. In general, the HIRLAM reanalysis system demonstrates considerable skill in reproducing the spatial and temporal evolution of the PW as depicted by the GPS estimations. Using a 0.2° horizontal resolution and 31 vertical levels, the HIRLAM reanalysis generates a PW time series that has, in comparison to that of the GPS estimates, an average offset of −0.1 mm and a root-mean-square difference of 2.4 mm. The average correlation between the PW time series fr...