The Baltic Sea Experiment (BALTEX) is one of the five continental-scale experiments of the Global Energy and Water Cycle Experiment (GEWEX). More than 50 research groups from 14 European countries are participating in this project to measure and model the energy and water cycle over the large drainage basin of the Baltic Sea in northern Europe. BALTEX aims to provide a better understanding of the processes of the climate system and to improve and to validate the water cycle in regional numerical models for weather forecasting and climate studies. A major effort is undertaken to couple interactively the atmosphere with the vegetated continental surfaces and the Baltic Sea including its sea ice. The intensive observational and modeling phase BRIDGE, which is a contribution to the Coordinated Enhanced Observing Period of GEWEX, will provide enhanced datasets for the period October 1999-February 2002 to validate numerical models and satellite products. Major achievements have been obtained in an improved understanding of related exchange processes. For the first time an interactive atmosphere-ocean-land surface model for the Baltic Sea was tested. This paper reports on major activities and some results.

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Based on data from 16 meteorological stations, trends in the amount of low clouds in Estonia have been investigated for the period 1955-1995. Analysis shows that the amount of low clouds has increased in March at all stations, in June at 12 stations and in September at eight stations. The amount of low clouds has decreased in May at seven stations and in October at five stations. Only trends that are significant at at least the 0.1 level were taken into account. Regression analysis shows that the increase in the amount of low clouds in March can be ascribed to changes in the frequencies of occurrence of European circulation patterns and/or to an increase in the amount of low clouds within the zonal circulation.