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A. G. Marshall, A. A. Scaife, and S. Ineson

vortex leads to increased refraction of planetary waves, which in turn decreases the deceleration of the vortex (e.g., Stenchikov et al. 2006 ). Thus, the impact of volcanic aerosols leads to an enhanced positive phase of the Arctic Oscillation (AO) and associated North Atlantic Oscillation (NAO; Thompson and Wallace 1998 ) that is most prominent in boreal winter and persists for up to 2 yr after each eruption (e.g., Robock and Mao 1992 ; Stenchikov et al. 2006 ). The observed AO response to

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R. R. Dickson, T. J. Osborn, J. W. Hurrell, J. Meincke, J. Blindheim, B. Adlandsvik, T. Vinje, G. Alekseev, and W. Maslowski

(1998 , 2000 ; Thompson et al. 2000) suggested that the NAO may be the regional manifestation of an annular (zonally symmetric) hemispheric mode of variability characterized by a seesaw of atmospheric mass between the polar cap and the middle latitudes in both the Atlantic and Pacific Ocean basins. A very similar structure is also evident in the Southern Hemisphere. They named this mode the Arctic Oscillation (AO) and showed that, during winter, its vertical structure extends deep into the

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Ran Zhang, Jiabei Fang, and Xiu-Qun Yang

-day lead ( Figs. 2a,f ), featuring a negative-phase Arctic Oscillation (AO) pattern ( Thompson and Wallace 1998 ). With time evolution (lead time from day −80 to day 0), the regional negative (positive) geopotential height anomaly centers over both North Pacific and southeast North America (northwest North America and around Hawaii) become clear, resembling a positive-phase Pacific–North American (PNA) pattern. Meanwhile, a negative-phase North Atlantic Oscillation (NAO) anomaly pattern gradually

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XiaoJing Jia, Hai Lin, and Xia Yao

regions nearby ( Rogers 1990 ; Hurrell 1995 , 1996 ). Although there exists some debate, many regard NAO as a regional display of the Arctic Oscillation (AO), which was defined first by Thompson and Wallace (1998) . It is well accepted that the AO/NAO is, to a significant degree, an internal mode of variability of the atmospheric circulation. The spatial structure and amplitude of the AO/NAO can be well simulated in atmospheric general circulation models (AGCM) forced with fixed external forcing

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Maria Flatau and Young-Joon Kim

1. Introduction The Madden–Julian oscillation (MJO) is primarily a tropical phenomenon, with its influence extending to the extratropics through the teleconnection reaching the polar regions in both hemispheres. This interaction appears to be stronger in the Northern Hemisphere (NH), where the largest MJO amplitudes coincide with the winter circulation. There is some evidence that the MJO influences the southern as well as northern polar regions. An MJO influence on the Arctic Oscillation (AO

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R. G. Graversen

ice volume has decreased by 40% relative to the situation prevalent from the 1940s through the 1970s ( Rothrock et al. 1999 ). Rigor et al. (2002) report that, in both the summer and winter season, changes of the wind stress might have given rise to larger areas with thin ice and leads in the eastern part of the Arctic Ocean that, in turn, possibly have contributed to the observed warming there. In the winter season, the changes of the wind stress are related to changes of the Arctic Oscillation

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Robert X. Black

1. Introduction It is becoming increasingly evident that longitudinally symmetric (or annular) modes of atmospheric variability, such as the Arctic oscillation (AO), strongly influence surface climate variability at mid- and high latitudes ( Thompson and Wallace 1998 ; Kerr 1999 ; Hartmann et al. 2000 ). In particular, the AO accounts for a large fraction of recent decadal climate trends in the northern high latitudes ( Hurrell 1995 ; Thompson et al. 2000 ). Thus, a thorough understanding of

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Linhao Zhong, Lijuan Hua, and Dehai Luo

contributes the most significantly to the BKS sea ice melting and warming because there is almost no concurrent downward IR increase found ( Fig. 8c ), which again suggests that the high local moisture contribution is only a manifestation of the sea ice melting. Corresponding to high local moisture contribution, the circulation ( Fig. 8d ) has a negative-phase Arctic Oscillation (AO−)-like pattern with an eastward-displaced positive anomaly that partly covers the BKS and with two negative anomalies

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Claude Frankignoul, Nathalie Sennéchael, and Pierre Cauchy

1. Introduction There is increasing evidence that the seasonal to decadal sea ice changes superimposed on the observed decline in Arctic sea ice cover affect the atmospheric circulation. Model studies have suggested that North Atlantic sea ice anomalies influence the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) and the North Atlantic storm track ( Magnusdottir et al. 2004 ; Alexander et al. 2004 ; Kvamstø et al. 2004 ), while North Pacific sea ice primarily influences the

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Cecilia Peralta-Ferriz, James H. Morison, John M. Wallace, Jennifer A. Bonin, and Jinlun Zhang

concern given their possible linkages with global climate, for example by controlling stratification in the sub-Arctic seas and thereby modulating convection and the meridional overturning circulation ( Aagaard and Carmack 1989 ; Hu et al. 2010 ). These changes have been linked to the Arctic Ocean circulation and climate variability ( Morison et al. 2000 , 2006 ). During the late 1980s and early 1990s, the leading mode of hemispheric surface atmospheric pressure, the Arctic Oscillation (AO

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