1. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
2. University of California, Department of Earth System Science, Irvine, CA 92697, USA.
3. Department of Atmospheric Sciences, University of Sao Paulo, Sao Paulo 05508–900, Brazil.
4. Centro de Energia Nuclear na Agricultura, University of Sao Paulo, Piracicaba 13416–000, Brazil.
5. Complex Systems Research Center, University of New Hampshire, Durham, NH 03824, USA.