Validation of Integrated Water Vapor from Numerical Models Using Ground-Based GPS, SSM/I, and Water Vapor Radiometer Measurements

Abstract

Abstract Time series of vertically integrated water vapor (IWV) derived for 25 ground-based global positioning system (GPS) sites in Sweden and Finland are used for validating the IWV from weather forecast models for a 3-month period from August through October of 1995. Results from analyses and forecasts of the Baltic Sea Experiment (BALTEX) Model and Europa Model [operational until December of 1999 at the German Weather Service (DWD)] at horizontal resolutions of 1/6° and 1/2° are evaluated. IWV retrievals from the Special Sensor Microwave Imager (SSM/I) for the Baltic Sea area and, for a second 6-month period in 1997, from a ground-based water vapor radiometer (WVR) at Potsdam are used additionally. The models reproduce the observed temporal and spatial variability of the IWV fields accurately, but a systematic humid bias of 2.5–3 kg m−2 is diagnosed versus GPS. However, radiosondes in the same area indicate a smaller bias of about 1.5–2 kg m−2 and hint at a slight dry bias in the GPS data. The standar...