We thank David Battisti, Conway Leovy, Dennis Lettenmaier, and the anonymous reviewers for their helpful suggestions. This work was supported by the National Science Foundation through the Climate Dynamics Program under Grant ATM-9805886. NCEP–NCAR reanalysis data were provided by the NOAA–CIRES Climate Diagnostics Center, Boulder, Colorado (http://www.cdc.noaa.gov/).
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