Validation of a regional weather forecast model with GPS data

Abstract

The atmospheric water vapor content is one of the most important parameters for the hydrological cycle. In order to investigate the energy and water balance over the Baltic Sea and its catchment, the hydrostatic regional weather forecast model HRM (High resolution Regional Model) of the German Weather Service (DWD) is validated against groundbased GPS data within the BALTEX (Baltic Sea Experiment) region and the PIDCAP period (Pilot Study for Intensive Data Collection and Analysis of Precipitation; August 1 to November 17, 1995). The vertically integrated water vapor content (IWV) derived from HRM shows a high correlation (coefficient = 0.935) and slightly (≈ 2.69 kg/m2) greater mean values than the GPS data mainly due to greater mean analyses data.Between 1995 and 1998 GPS/MET aboard the Micro-Lab 1 successfully demonstrated the radio occultation technique to probe the Earth's atmosphere through its refraction effects on the signals transmitted by the GPS satellites. Profiles of the water vapor can be obtained from the GPS derived refractivity by using the temperature profiles of the HRM model. For a comparison of the vertical distribution of the specific humidity these water vapor profiles are used. Also lower values than with HRM were found. A comparison of the vertically IWV as derived from GPS/MET and from HRM shows a high correlation (coefficient = 0.90).