1. Uni Bjerknes Centre, Allegaten 55, NO-5007, Bergen, Norway;
2. Bjerknes Centre for Climate Research, Allegaten 55, NO-5007, Bergen, Norway;
3. Department of Atmospheric Sciences, University of Alaska Fairbanks, International Arctic Research Center, 930 Koyukuk Drive, Fairbanks, AK 99775, USA;
4. National Centre for Earth Observation, University of Reading, Whiteknights, PO Box 238, Reading, RG6 6AL, UK;
5. University of Bergen, Geophysical Institute, Allegaten 70, NO-5007, Bergen, Norway