1. Institute for Terrestrial and Planetary Atmospheres/School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794–5000, USA.
2. Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE), CNRS, University of Grenoble, BP96, 38402 St. Martin d’Hères Cedex, France.