The authors offer their gratitude for support through the Chinese Scholarship Council, the Office of Science (BER) and the National Science Foundation, Grant ATM-0649512. In addition, we thank Drs. Sukyoung Lee, Michelle L’Heureux, Mu Mu, Zenghao Qin, and Lixin Wu and two anonymous reviewers for offering helpful suggestions that improved the quality of this work. We also thank the European Centre for Medium-Range Weather Forecasts for providing us with the ERA-40 reanalysis data and the Climate Analysis Branch of the NOAA Earth System Research Laboratory/Physical Sciences Division for providing us with the NCEP–NCAR Reanalysis data. In addition, we acknowledge the NOAA Climate Prediction Center and the Climate Analysis Center of NCAR for providing us with the climate indices.
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