1. Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA.
2. National Oceanic and Atmospheric Administration (NOAA), National Climatic Data Center, Boulder, CO 80305, USA.
3. Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
4. Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA.