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Masashi Kohma, Seiya Nishizawa, and Shigeo Yoden

maximum phase. Asymmetry of the time variations of SSW and VI events is characterized by the difference in the acceleration process of the stratospheric westerly wind: deceleration due to wave driving can be rapid, while acceleration associated with radiative cooling is generally more gradual. As for the slow variations in the Northern Hemisphere troposphere, the Arctic Oscillation (AO) is one of the well-known slow variations. The term was coined by Thompson and Wallace (1998) as the leading

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Dingzhu Hu and Zhaoyong Guan

:// . 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. , , 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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Yuki Kanno, John E. Walsh, and Toshiki Iwasaki

), North Atlantic Oscillation (NAO), and Arctic Oscillation (AO) affect climate variability over NA during winter ( Rogers 1984 ; Thompson and Wallace 1998 ; Thompson and Wallace 2001 ; Walsh et al. 2001 ; Cellitti et al. 2006 ; Marinaro et al. 2015 ). Figure 1 shows the 500-hPa manifestations of these large-scale modes of variability. The PNA and TNH patterns are related to variations in sea surface temperature in the tropical Pacific Ocean, especially El Niño–Southern Oscillation (ENSO) ( Yu

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Gaeun Kim, Sinil Yang, and Woo-Seop Lee

circulatory systems that affect East Asia, the ENSO and Arctic Oscillation (AO) play an important role in predicting the East Asian winter climate. It is generally accepted that the AO could impact the East Asia winter monsoon (EAWM) in association with a stronger East Asia trough or an anomalous anticyclonic flow over the Urals at the midtroposphere ( Luo et al. 2017 ; Yao et al. 2017 ; Luo et al. 2016a , b ; Overland et al. 2015 ; Cohen et al. 2014 ; Takaya and Nakamura 2013 ; Tang et al. 2013

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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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Andrew W. Robertson

1. Introduction The Arctic oscillation (AO) emerges as the leading empirical mode of wintertime monthly sea level pressure (SLP) over the Northern Hemisphere (NH) ( Lorenz 1951 ; Kutzbach 1970 ; Trenberth and Paolino 1981 ; Wallace and Gutzler 1981 ; Thompson and Wallace 1998 ). Its spatial structure is characterized by anomalous SLP of one sign throughout the Arctic Basin, with anomalies of the opposite sign centered over the Azores and, more weakly, over the North Pacific (see Fig. 1f

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Y. Peings, D. Saint-Martin, and H. Douville

evidence that the Siberian snow cover, particularly in October, is a good precursor of the Arctic Oscillation (AO; Thompson and Wallace 1998 ), which is also described as the northern annular mode (NAM). The snow cover extent also correlates well with the North Atlantic Oscillation (NAO), which is sometimes considered as a regional signature of the annular mode ( Bojariu and Gimeno 2003 ). This lagged correlation has important implications for seasonal forecasting, as it could lead to improved

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Patricia DeRepentigny, L. Bruno Tremblay, Robert Newton, and Stephanie Pfirman

and the total volume of ice in the summer have been steadily decreasing since 1987. The large-scale pattern of sea level pressure in the Arctic can be characterized, to first order, by the Arctic Oscillation (AO) ( Thompson and Wallace 1998 ), the first EOF of Northern Hemisphere sea level pressure, or by the northern annular mode (NAM) ( Thompson and Wallace 2001 ), a closely related high-latitude pattern. Rigor et al. (2002) showed that the AO explains 52% of the variance of sea level pressure

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Masahiro Watanabe and Fei-Fei Jin

1. Introduction A concept of Arctic Oscillation (AO), or the northern annular mode, proposed by Thompson and Wallace (1998) has recently provided a different view of the low- frequency atmospheric variability from the classic teleconnection. The AO, defined by the leading empirical orthogonal function (EOF) to the Northern Hemisphere sea level pressure (SLP) anomalies, has a hemispheric extent dominated by a zonally uniform structure as shown by the AO-covariant height anomalies ( Fig. 1a

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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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