Validation of the NWP Model HRM with Groundbased GPS Data

The atmospheric water vapor is a very important variable for the hydrological cycle and for short term numerical weather prediction. Groundbased GPS data are applied to validate the vertically integrated water vapor (IWV) as derived with the HRM model (High resolution Regional Model) of the German Weather Service (DWD) within the BAL.TEX (Baltic Sea Experiment) region. Data of the PIDCAP period (Pilot Study for Intensive Data Collection and Analysis of Precipitation; August 1 to November 17,1995) from Sweden and Finland and of the first month (May 2000) of GPS measurements processed by the Geo Forschungs Zentrum (GFZ, Potsdam, Germany) within the BRIDGE baseline period (October 1999 to December 2002) are used. The IWV of the HRM model with ECMWF analysis data as initial fields show significantly lower mean differences to the GPS IWV data than the HRM Twv with the EM3AN analysis data of the Europa-Model of the DWD. The IWV differences of the HRM model and the GPS data can mainly be explained by the differences between the analysis data and the GPS data. The IWVs derived from HRM model are highly correlated with the GPS data (i.e. with a correlation coefficient of 0.937 for the PIDCAP period and a correlation coefficient of 0.881 for May 2000). Q 2001 Else&r Science Ltd. All rights reserved