1. Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, Colorado
2. Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado
3. Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, and Bureau of Meteorology, Melbourne, Victoria, Australia
4. Department of Physics, University of Toronto, Toronto, Ontario, Canada
5. Department of Applied Physics and Applied Math, and Department of Earth and Environmental Sciences, Columbia University, New York, New York