The seasonal footprinting mechanism in large ensemble simulations of the second generation Canadian earth system model:
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The seasonal footprinting mechanism in large ensemble simulations of the second generation Canadian earth system model: uncertainty due to internal climate variability Shangfeng Chen1 · Bin Yu2 Received: 23 October 2019 / Accepted: 24 July 2020 / Published online: 30 July 2020 © The Author(s) 2020
Abstract Previous studies indicated that the wintertime North Pacific Oscillation (NPO) could exert marked impacts on the following winter El Niño-Southern Oscillation (ENSO) via the seasonal footprinting mechanism (SFM). Here, we examine this winter NPO-ENSO relationship in a 50-member ensemble of historical simulations conducted with the Canadian Centre for Climate Modeling and Analysis second generation Canadian Earth System Model (CanESM2) over the period of 1950–2005. The observed NPO pattern, featured by a meridional dipole atmospheric anomaly over the North Pacific, can be well reproduced by all of the 50 ensemble members. The multi-member ensemble (MME) mean can well simulate the observed NPO-ENSO relationship, as well as the SFM process. However, there exists a large spread of the results among the 50 members due to internal climate variability. Internal climate variability influences the winter NPO-ENSO relationship through modulating the subtropical center of the NPO. Specifically, the ensemble members with high NPO-ENSO correlations tend to have strong atmospheric anomalies over the subtropical North Pacific in winter. The atmospheric circulation anomaly brings strong sea surface temperature and precipitation anomalies in the tropical central Pacific and westerly wind anomalies over the tropical western Pacific in the following spring. These anomalies sustain in the following seasons and eventually lead to ENSO events in the following winter. Keywords NPO · ENSO · Seasonal footprinting mechanism · Large ensemble simulations · Internal climate variability
1 Introduction The El Niño-Southern Oscillation (ENSO) is the leading air-sea coupled mode over the tropical Pacific on the interannual timescale (Bjerknes 1969; Philander 1990; Neelin et al. 1998; Wang et al. 2000; Alexander et al. 2002). ENSO events have substantial influences on ecosystems, marine, crop growth, extreme weather and climate events over many regions surrounding the Pacific and remote areas through oceanic and atmospheric teleconnections (Luo et al. 2011; Chiang and Sobel 2002; Huang et al. 2004; McPhaden,
* Shangfeng Chen [email protected] 1
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Climate Research Division, Environment and Climate Change Canada, Toronto, ON, Canada
2
2002; Wu et al. 2003; Song et al. 2017; Zhang et al. 2017, 2019a; Chen et al. 2018a, b, c, d; Jin et al. 2018; Chen and Song 2019; Wang et al. 2019; Chen et al. 2019; and references therein). For example, ENSO can significantly affect East Asian climate via altering the atmospheric circulation anomalies over the subtropical western North Pacific (Wang et al. 2000; Xie et al. 2009; Z
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