1. Remote Sensing Division, Swedish Meteorological and Hydrological Institute, Folkborgsvagen 1, 60176 Norrköping, Sweden;
2. Department of Meteorology, Stockholm University, Stockholm, Sweden;
3. School of Environmental Sciences, University of East Anglia, Norwich, UK;
4. Rossby Center, Swedish Meteorological and Hydrological Institute, Norrköping, Sweden;
5. Science Directorate, NASA Langley Research Center, Hampton, Virginia, USA