1. Alfred-Wegener-Institute for Polar and Marine Research in the Helmholtz Association, Telegrafenberg A 43, 14473 Potsdam, Germany
2. Climate and Global Change Research, Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
3. Norwegian Institute for Air Research, P.O. Box 100, 2027 Kjeller, Norway
4. Alfred-Wegener-Institute for Polar and Marine Research in the Helmholtz Association, Bürgermeister-Schmidt-Straße 20, 27568 Bremerhaven, Germany