Investigation of the atmospheric water budget of the BALTEX area using NCEP/NCAR reanalysis data

The Baltic Sea ExperimentBALTEX is the European regional project of GEWEX. The aim ofBALTEXis to improve the knowledge of the water and energy cycle of the Baltic Sea including its catchment area(the BALTEX area). In this study the NCEP/NCAR reanalysis data (Kalnay et al.Bull. Am. Meteorol.Soc., 1996,77, 437—471) are used to derive the mean atmospheric water budget over the BALTEX area.For this purpose the horizontal water vapour fluxes are calculated. In the long-term mean (here 1948–2000) the vertically integrated divergence of these fluxes must balance evaporation minus precipitation.The latter two are provided by the NCEP/NCAR reanalyses. The water budget over the BALTEX areais, however, not closed. An error estimation is performed. The divergence of the water vapour flux iscorrected due to the mass balance correction technique (Alestalo,Tellus, 1981,33, 360—371). Largedifferences are obtained between the precipitation given by the NCEP/NCAR reanalysis and by theanalysis of the observations by Rubel and Hantel (Meteorol. Atmos. Phys., 2001,77, 155—166). Withthese analysed precipitation data and the corrected divergence of the water vapour fluxes the imbalanceof the water vapour budget could be remarkably reduced.