1. Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, FI-70211, Kuopio, Finland
2. Finnish Meteorological Institute, Kuopio Unit, P.O. Box 1627, FI-70211, Kuopio, Finland
3. Department of Atmospheric Sciences, University of Washington, 708 ATG Building, 98195, Seattle, WA, USA
4. Finnish Meteorological Institute, P.O. Box 503, FI-00101, Helsinki, Finland