1. SMHI, Nya Varvet 31, SE-42671 Västra Frölunda, Sweden and Dept. of Oceanography, Earth Sciences Centre, Göteborg University, Box 460, SE-405 30 Göteborg, Sweden;
2. Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland;
3. Department of Mechanics, Tallinn University of Technology, Ehitajate tee 5, EE-19086 Tallinn, Estonia;
4. Department of Meteorology/Physical Oceanography, Stockholm University, SE-10691 Stockholm, Sweden