The asymmetric impacts of ENSO modoki on boreal winter climate over the Pacific and its rim
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The asymmetric impacts of ENSO modoki on boreal winter climate over the Pacific and its rim Linqiang He1 · Xin Hao1,2 · Tingting Han1,2 Received: 24 October 2019 / Accepted: 24 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The El Niño–Southern Oscillation (ENSO) Modoki phenomenon has a substantial influence on regional climate. In this study, the results derived from observational and reanalyzed datasets show that the boreal winter climate anomalies over the Pacific and its rim in the different phases of ENSO Modoki are asymmetric during 1979–2017. During El Niño Modoki, an upper-level zonal “convergence–divergence–convergence” anomaly occurred in the Walker circulation over the Pacific sector, associated with anomalous ascending (descending) in the central side (both sides), leading to a wet “boomerang” pattern of rainfall anomalies in the tropical Pacific Ocean. Consequently, a drier winter occurred in Philippines, and warming and drying occurred in western Australia and northern South America. Meanwhile, a dipolar pattern with the wet south and the dry north in the United States occurred, accompanied by a Pacific/North American-like teleconnection. During La Niña Modoki, a roughly reversed Walker circulation anomaly and deeper Hadley circulation anomalies were associated with the strong air–sea feedback, which caused stronger rainfall anomalies in the Pacific Ocean. On land, anomalies of surface temperature and rainfall over the tropical Pacific Rim were more intense compared with El Niño Modoki. However, owing to the lack of a Pacific/North American anomaly, fewer anomalies occurred over the mid-latitude North America. In numerical experiments, the response to the different phases of ENSO Modoki basically reproduces the asymmetric climate anomalies in boreal winter, further confirming that the asymmetry can be partly attributed to tropical sea surface temperature anomalies. Keywords ENSO modoki · Boreal winter climate · Asymmetry · Air–sea feedback
1 Introduction El Niño Modoki is known as a coupled ocean–atmosphere phenomenon associated with the tripole pattern of sea surface temperature (SST) anomalies in the equatorial Pacific, which is different from the canonical El Niño (Ashok et al. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05395-z) contains supplementary material, which is available to authorized users. * Xin Hao [email protected] 1
Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters/Key Laboratory of Meteorological Disaster, Ministry of Education, Nanjing University of Information Science and Technology, Nanjing 210044, China
Nansen‑Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
2
2007; Weng et al. 2007). When El Niño Modoki occurs, warm SST anomalies are observed over the central equatorial Pacific and cold SST anomalies occur in its east and west sides, and the opposite pattern i
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