The Interdecadal Pacific Oscillation (IPO) and its impacts on precipitation over eastern China during the last millennium are investigated through analyzing two 1000 year global climate model simulations. Results show that the model does not simulate a prolonged period of negative IPO before A.D. 1300 suggested by the proxy reconstruction, although it does simulate centennial periods of negative and positive IPO. The simulated IPO exhibits several low-frequency oscillations, including 10-23, 30-33, 35-70, and 85-110 years. However, it remains an open question whether simulated IPO oscillations longer than bidecadal mode can be or not be considered as essentially internal modes of variability. The simulations indicate that precipitation over eastern China is associated with the IPO. When the strongest IPO signal of 53-77 year oscillation occurs, the summer precipitation goes of opposite sign over North China (NC) and the middle and lower Yangtze River Vally (MLYRV), i.e., dipole mode such as the “flood-in-south and drought-in-north” pattern that occurs during the positive IPO episodes and vice versa. While coherent mode is dominant when the relatively weak IPO signal occurs, and warm phases of the IPO coincide with coherent drought and vice versa. The association between 53-77 year oscillation of the IPO and precipitation in NC is more marked than that in the MLYRV. Our results suggest that the internal variability of climate system like the IPO may play an important role in precipitation over eastern China, at least on the 53-77 year oscillation.
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The authors are deeply grateful to the Editor and the two anonymous referees for providing thorough reviews and constructive comments, which improved significantly our manuscript. We also thank G.M. MacDonald for providing their PDO index data (http://www.ncdc. noaa.gov/data-access/paleoclimatology- data/datasets/climate-reconstruction) used in Figure 2. This work is supported by the National Basic Research Program of China (grants 2013CB955904, 2013CB955902, and 2010CB950102), the National Natural Science Foundation of China (grant 41230524), the Fundamental Research Funds for the Central Universities (grant 1191320019), the 2013 Yunnan Project for the Introduction of Advanced Talents (grant 2013HA024), the Fundamental Research Funds for the Central Universities, and the grant from the Office of Science (BER), U.S. Department of Energy.