[1] Univ Reading, Dept Meteorol, Ctr Global Atmospher Modelling, Reading RG6 6BB, Berks, England
[2] Hadley Ctr Climate Predict & Res, Met Off, Exeter EX1 3PR, Devon, England
[3] Free Univ Brussels, Dept Geog, B-1050 Brussels, Belgium
[4] Alfred Wegener Inst Polar & Marine Res, D-27515 Bremerhaven, Germany