Dominant wintertime surface air temperature modes in the Northern Hemisphere extratropics
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Dominant wintertime surface air temperature modes in the Northern Hemisphere extratropic Hae‑Li Park1 · Kyong‑Hwan Seo1,2 · Baek‑Min Kim3 · Jin‑Yong Kim1 · S.‑Y. Simons Wang4 Received: 21 January 2020 / Accepted: 2 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Recent observations showed that boreal winter exhibits significant cooling events in the Eurasian and North American continents despite the global warming trend. To better understand the boreal winter surface air temperature (SAT) variability and its physical characteristics, we investigated the three distinct Empirical Orthogonal Function (EOF) modes of the extratropical 2-m air temperature (T2m) variation and found that each mode can be related to the well-known physical processes: The first mode is characterized by the coherent change of wintertime SAT anomalies over northern Eurasia and central-eastern North America and it is found that snow cover variation in the Eurasian region can modulate Arctic Oscillation (AO) circulation through the troposphere–stratosphere interaction, which can affect wintertime SAT in the two continents. The second leading mode shows warm anomalies over the North Pacific especially around the Bering Strait and cold anomalies over most of Canada and the central part of North America. Associated with this mode, La Niña-like sea surface temperature (SST) anomaly can modulate the North American SAT variability through the generation of the tropospheric Pacific–North American (PNA) teleconnection pattern. The third mode represents warm anomalies over the Barents and Kara (B–K) seas and cold anomalies over East Asia. Sea ice loss over the B–K sea is analyzed to be closely related to the SAT variability over the East Asian region. Keywords Extratropical 2-m air temperature · Winter climate · Dominant mode · Teleconnection · Rossby wave
1 Introduction It is evident that the global SAT trend is increasing due to ongoing anthropogenic global warming. However, the boreal winter exhibit severe cold winters in both the Eurasian and North American continents. Some studies have proposed that this extreme weather in Eurasia and North America can be linked to Arctic sea ice loss and/or positive Eurasian * Kyong‑Hwan Seo [email protected] 1
Division of Earth Environmental System, Department of Atmospheric Sciences, Pusan National University, Busan 46241, South Korea
2
Research Center of Climate Sciences, Pusan National University, Busan, South Korea
3
Department of Environmental Atmospheric Sciences, Pukyong National University, Yongso‑ro 45, Nam‑Gu, Busan, South Korea
4
Department of Plants, Soils and Climate, Utah State University, Logan, UT, USA
snow cover anomalies (Cohen et al. 2012, 2014b; Jaiser et al. 2012; Kug et al. 2015; Sun et al. 2016; Tachibana et al. 2019), but whether Arctic sea ice or Eurasian snow cover plays a key role in forcing cold winter in the extratropic is still controversial (Kumar et al. 2010; Screen et al. 2013, 2018; Gerber et al. 2014; Li et al. 2015; Per
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