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Thomas L. Delworth and Keith W. Dixon

1. Introduction The dominant pattern of atmospheric variability during winter over the extratropical Northern Hemisphere (NH) is referred to as the Arctic oscillation (AO) ( Thompson and Wallace 1998 , 2000 ) and is characterized by a redistribution of mass between the polar latitudes and midlatitudes. A positive phase of the AO corresponds to reduced sea level pressure over the Arctic and increased westerly winds at midlatitudes. The largest changes in midlatitudes associated with the AO

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Guillaume Gastineau, Javier García-Serrano, and Claude Frankignoul

influence the underlying troposphere by downward propagation of circulation anomalies. The influence of the Eurasian snow cover has received most attention in autumn, as it shows a statistically significant relation with the following winter Arctic Oscillation (AO) and North Atlantic Oscillation (NAO), from December to March ( Cohen et al. 2007 ; Déry and Brown 2007 ; Allen and Zender 2010 ; Cohen et al. 2012 ). Sea ice concentration (SIC) changes may also influence the atmosphere. The most reported

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Wolfgang Buermann, Benjamin Lintner, and Céline Bonfils

winter Arctic Oscillation. Using simple correlation analysis, the June precipitation index is observed to project similar spatial patterns onto the late winter/early spring surface temperature and soil moisture proxy fields as the boreal winter AO. We next describe the results of a technique—canonical correlation analysis (CCA)—that isolates coupled patterns of variability between two fields. The CCA framework represents a valuable tool for understanding how the development of anomalous, early

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Hae-Jeong Kim and Joong-Bae Ahn

1. Introduction The Arctic Oscillation (AO), characterized by oscillation of atmospheric pressure between the Arctic and the midlatitudes, is one of the most dominant patterns of hemispheric scale variability in the Northern Hemisphere ( Thompson and Wallace 2000 ). Numerous studies have revealed the impacts of the AO on the boreal winter climate over the middle and high latitudes of North America, Europe, and East Asia (e.g., Higgins et al. 2002 ; Kolstad et al. 2010 ; Park et al. 2011

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Liwei Jia, Xiaosong Yang, Gabriel Vecchi, Richard Gudgel, Thomas Delworth, Stephan Fueglistaler, Pu Lin, Adam A. Scaife, Seth Underwood, and Shian-Jiann Lin

fluctuations in the speed of the stratospheric circumpolar westerly jet (i.e., polar vortex) that forms in winter and spring. For example, over the Northern Hemisphere, a weakening of the stratospheric polar vortex shifts the tropospheric jet stream southward (often associated with the negative phase of the Arctic Oscillation), leading to low temperatures over northern Eurasia and the eastern United States ( Thompson et al. 2002 ; Kidston et al. 2015 ). Several studies have shown seasonal predictive skill

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A. J. Miller, S. Zhou, and S-K. Yang

1. Introduction The Arctic Oscillation (AO) in conjunction with the North Atlantic Oscillation (NAO) is a leading mode of climate variability in the Northern Hemisphere extratropical circulation (e.g., Thompson and Wallace 1998 , 1999). The phase of this phenomenon at upper levels is strongly related to the strength and location of the polar jet stream. Specifically, it has been shown that this leading pattern of intraseasonal climate variability is related to day-to-day weather, particularly

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Dingzhu Hu and Zhaoyong Guan

://doi.org/10.1175/JCLI-D-15-0851.1 . 10.1175/JCLI-D-15-0851.1 Hu , J. , T. Li , and H. Xu , 2018 : Relationship between the North Pacific Gyre Oscillation and the onset of stratospheric final warming in the northern Hemisphere . Climate Dyn. , https://doi.org/10.1007/s00382-017-4065-3 , in press. 10.1007/s00382-017-4065-3 Hurwitz , M. M. , P. A. Newman , and C. I. Garfinkel , 2012 : On the influence of North Pacific sea surface temperature on the Arctic winter climate . J. Geophys. Res

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Qigang Wu

as an “atmospheric bridge” that links interannual SST fluctuations in the tropical Pacific with oceanic variations at higher latitudes ( Alexander et al. 2002 ; Lau and Nath 1996 ). Additional studies have shown that components of the large-scale extratropical atmospheric variability in the NH wintertime can influence the tropical atmospheric and/or SST variations. Thompson and Wallace (2000) demonstrate that the north annular mode [NAM; sometimes called the Arctic Oscillation (AO; Thompson

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Chih-Pei Chang and Mong-Ming Lu

significant relationship with ENSO, most research of SH variability has been concentrated in its relationship with the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) ( Gong et al. 2001 ; Wu and Wang 2002 ; Park et al. 2011 ). The results suggest that a relationship may exist at the interdecadal scale but not the interannual scale. 2. Intraseasonal phase change Recent research in intraseasonal oscillations (ISO), particularly the Madden–Julian oscillation ( Wheeler and Hendon 2004 ), has

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Haibo Bi, Yunhe Wang, Yu Liang, Weifu Sun, Xi Liang, Qinglong Yu, Zehua Zhang, and Xiuli Xu

circulation appears, together with negative anomalies over the Siberian side ( Wu et al. 2005 ). Concomitant with the geopotential height (GH) anomaly distribution pattern at 850 hPa, the GH anomaly at 300 hPa over the Beaufort high and Greenland (not shown) indicates a barotropic structure. In contrast, the SLP anomalies associated with the Arctic Oscillation (AO; corresponding to the leading mode of SLP anomalies in the Arctic) is annular (not shown), which is not a primary contributor to the recent

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