1. Jet Propulsion Laboratory, California Institute of Technology, MS 300-235, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
2. Division of Geological and Planetary Sciences, California Institute of Technology, MS 170-25, Pasadena, CA 91125, USA.
3. Joint Center for Earth System Science, Department of Meteorology, University of Maryland at College Park, College Park, MD 20742, USA.