Centre for Atmospheric Science, University of Cambridge, Cambridge, UK

now at: Columbia University, Center for Climate Systems Research, NASA Goddard Institute for Space Studies, New York, USA

Met Office, Exeter, UK

Lancaster Environment Centre, University of Lancaster, Lancaster, UK

Centre for Atmospheric Science, University of Cambridge, Cambridge, UK

Department of Earth Sciences, Royal Holloway, University of London, London, UK

Centre for Atmospheric Science, University of Cambridge, Cambridge, UK