Atmospheric and Environmental Research, Inc., Lexington, MA, USA

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA

now at: NOAA Geophysical Fluid Dynamics Laborator, Princeton, NJ, USA

Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA

now at: Pacific Northwest National Laboratory, Richland, WA, USA