Projection of winter NPO-following winter ENSO connection in a warming climate: uncertainty due to internal climate vari
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Projection of winter NPO-following winter ENSO connection in a warming climate: uncertainty due to internal climate variability Shangfeng Chen 1
& Bin Yu
2
Received: 24 December 2019 / Accepted: 25 June 2020/ # The Author(s) 2020
Abstract
Previous observational and modeling studies indicate that the wintertime North Pacific Oscillation (NPO) could significantly impact the following winter El Niño-Southern Oscillation (ENSO) variability via the seasonal footprinting mechanism (SFM). This study explores climate projections of this winter NPO-ENSO relation in a warming climate based on a 50-member large ensemble of climate simulations conducted with the second-generation Canadian Earth System Model (CanESM2). The ensemble mean of the 50 members can well reproduce the observed winter NPO pattern, the NPO-ENSO relationship, and the SFM process over the historical period 1950–2003. These 50 members are then employed to examine climate projections of the NPO-ENSO connection over the anthropogenic forced period 2020–2073. Results indicate that there exists a large spread of projected NPO-ENSO connections across these 50 ensemble members due to internal climate variability. Internal climate variability brings uncertainties in the projection of the winter NPO-ENSO connection originally seen in projected changes of the subtropical center of the winter NPO. The spread of projections of winter NPOassociated atmospheric anomalies over the subtropical North Pacific further results in various responses in the projections of winter and spring precipitation anomalies over the tropical North Pacific, as well as spring zonal wind anomalies over the tropical western Pacific, which eventually lead to uncertainties in the projection of the sea surface temperature anomalies in the tropical central-eastern Pacific from the following summer to winter. Keywords NPO . ENSO . Climate projection . Uncertainty . Internal climate variability
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10584-02002778-3) contains supplementary material, which is available to authorized users.
* Shangfeng Chen [email protected] Extended author information available on the last page of the article
Climatic Change
1 Introduction The El Niño-Southern Oscillation (ENSO) is the dominant mode of the atmosphere-ocean coupled climate variability in the tropical Pacific on the interannual timescale (Bjerknes 1969; Philander 1990; Alexander et al. 2002). ENSO exerts considerable impacts on variations of weather and climate, marine ecosystems, and agriculture, as well as human health over many portions of the world (e.g., Gray 1984; Chiang and Sobel 2002; McPhaden 2002; Kovats et al. 2003; Huang et al. 2004; Chan 2005; Graf and Zanchettin 2012; Chen et al. 2013; Oluwole 2015; Song et al. 2017; McGregor and Ebi 2018; Chen and Song 2019; and references therein). For instance, the catastrophic Yangtze River floods in the summer of 1998, which have been attributed largely to the strong 1997/1998 El Niño, resul
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