Validation of NWP Mesoscale Models with Swiss GPS Network AGNES

Abstract

The importance of water vapor for the hydrological cycle of the earth and the atmosphere is well known but difficult to study and sample. In this respect, the vertically integrated water vapor (IWV) derived from global positioning system (GPS) delay is a potential source of valuable weather information. Because of the relatively dense station distribution, both the temporal and horizontal variability of water vapor are well captured by the GPS. This makes GPS data well suited for numerical weather prediction (NWP) models. In this paper the automated GPS network of Switzerland (AGNES) is used for calculation of IWV and for comparison with radiosonde data and two NWP mesoscale models from MeteoSwiss named Local Model (LM) and Swiss Model (SM). Reasonably good agreement between GPS and radiosonde data is reported. It has been identified that in some particular weather situations with low stratus clouds and temperature inversion, the radiosonde significantly overestimates the water vapor amount. The LM and SM verification with GPS data indicates good agreement during the winter period (November 2000?March 2001) and high variability and bias in the summer period (August 2000). The monthly mean IWV values from GPS and LM show a systematic deviation over the Swiss plateau region and a very good agreement for the high-altitude alpine station, Andermatt. The capability of GPS in monitoring the atmospheric phenomena has been demonstrated. Unrealistic IWV at Jungfraujoch (?3600 m MSL) caused by GPS antenna problems is reported.