Equatorial western-central Pacific SST responsible for the North Pacific Oscillation-ENSO sequence

Suqiong Hu aKey Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC - FEMD), Nanjing University of Information Science and Technology, Nanjing, China

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Wenjun Zhang aKey Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC - FEMD), Nanjing University of Information Science and Technology, Nanjing, China

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Masahiro Watanabe bAtmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan

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Feng Jiang aKey Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC - FEMD), Nanjing University of Information Science and Technology, Nanjing, China

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Fei-Fei Jin cDepartment of Atmospheric Sciences, School of Ocean and Earth Science and Technology, University of Hawaiʻi at Mānoa, Honolulu, HI, USA

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Han-Ching Chen aKey Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC - FEMD), Nanjing University of Information Science and Technology, Nanjing, China

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Abstract

El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Pacific, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn influence the occurrence of ENSO events. The winter North Pacific Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Pacific, has been recognized as a potential precursor for ENSO development. This study demonstrates that the pre-existing winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western-central Pacific. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979–2021, significant SST anomalies emerge in the equatorial western-central Pacific in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, significant SST anomalies are not observed in the equatorial western-central Pacific during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western-central Pacific can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO-ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western-central Pacific. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical-extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Wenjun Zhang, zhangwj@nuist.edu.cn

Abstract

El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Pacific, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn influence the occurrence of ENSO events. The winter North Pacific Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Pacific, has been recognized as a potential precursor for ENSO development. This study demonstrates that the pre-existing winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western-central Pacific. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979–2021, significant SST anomalies emerge in the equatorial western-central Pacific in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, significant SST anomalies are not observed in the equatorial western-central Pacific during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western-central Pacific can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO-ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western-central Pacific. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical-extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Wenjun Zhang, zhangwj@nuist.edu.cn
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