This study aims to better understand the ENSO impacts on climate anomalies over East Asia in early winter (November-December) and late winter (January-February). In particular, the possible mechanisms during early winter are investigated. The results show that ENSO is associated with a Rossby wave train emanating from the tropical Indian Ocean toward East Asia (denoted as tIO-EA) in early winter. This tIO-EA wave train in El Niño (La Niña) is closely related to a weakening (strengthening) of the East Asian trough, and thereby a weakened (strengthened) East Asian winter monsoon and warm (cold) temperature anomalies over northeastern China and Japan. By using partial regression analysis and numerical experiments, we identify that the formation of tIO-EA wave train is closely related to precipitation anomalies in the tropical eastern Indian Ocean and western Pacific (denoted as eIO/wP). In addition, the ENSO-induced North Atlantic anomalies may also contribute to formation of the tIO-EA wave train in conjunction with the eIO/wP precipitation. The response of eIO/wP precipitation to ENSO is stronger in early winter than in late winter. This can be attributed to the stronger anomalous Walker circulation over the Indian Ocean, which in turn is caused by higher climatological SST and stronger mean precipitation state in the Indian Ocean during early winter.
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Acknowledgments. We thank the editor Dr. Agus Santoso and three anonymous reviewers for their constructive suggestions, which helped to significantly improve the paper. This work was supported jointly by the National Natural Science Foundation of China (Grants 41721004, 41961144025, and 42005032), the National Key Research and Development Program of China (2018YFC1506003), and the Jiangsu Collaborative Innovation Center for Climate Change. CIG is supported by the ISF-NSFC joint research program (3259/19). We are grateful to Dr. Sen Zhao, Prof. Jianping Li, and Dr. Yanjie Li for making the Rossby wave tracing code readily The authors declare no potential conflict of interest.
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- Indian Ocean