1. Department of Geosciences, and Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802, USA.
2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3. Department of Meteorology and Atmospheric Science, and Center on Advanced Data Assimilation and Predictability Techniques, The Pennsylvania State University, University Park, PA 16802, USA.