1. University of Nebraska Public Policy Center, 215 Centennial Mall South, Suite 401, Lincoln, NE 68508, USA.
2. Department of Computer Science and Engineering, University of Nebraska-Lincoln, 220 Schorr Center, Lincoln, NE 68588, USA.
3. Earth and Atmospheric Sciences, University of Nebraska-Lincoln, 305A Bessey Hall, Lincoln, NE 68588, USA.