Impacts of cloud and turbulence schemes on integrated water vapor: comparison between model predictions and GPS measurements

Structures in atmospheric Integrated Water Vapor (IWV) have been studied fo r the three successive cyclones, Kerstin, Liane and Monika, which controlle d the meteorological conditions in the Baltic Sea catchment region in the p eriod from 28 August to 5 September 1995 (parr of the PIDCAP observational campaign defined within BALTEX). Several model predictions of these cyclone s have been performed with a regional atmospheric general circulation model (RACMO). The impact of two different versions of the model physics package (standard ECHAM4 and a revised version with modifications in the cloud and turbulence scheme) has been investigated. Model predicted IWV has been eva luated with GPS station data from several stations in Sweden and Finland. F or the most strongly developed cyclone Monika, the revised scheme generates more pronounced IWV structures, with well defined bands of high and low va lues of IWV curving into the center of the cyclone. In particular, the shap e of the minima are in better agreement with the GPS station data, and the consistency between two subsequent model forecasts is also larger with the revised physics package. For the weaker systems, Kerstin and Liane, results from both model versions are very similar.