Near real time GPS water vapor monitoring for numerical weather prediction in Germany

Within the framework of the Helmholtz Association Strategy Project "GPS Atmosphere Sounding" (GASP), an operational monitoring of integrated water vapor was established using 170 GPS sites in Germany and neighboring countries. The product, which can be obtained within 12-15 minutes of computer time on a single Linux PC, is generated each hour with a 30-minute time resolution and an accuracy of +/-1-2 mm in the precipitable water vapor. The GPS estimates are regularly validated using collocated instruments and the local model (LM) of the German Weather Service (DWD). First experiments for numerical weather predictions are performed at DWD and showed 2% improvement for the relative humidity in a 12-hour forecast, whilst the impact on the precipitation forecast over 24 hours is mixed up to now.