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Christian Blume, Katja Matthes, and Illia Horenko

measure the vortex strength. In this work, a method is proposed that extends and combines the zonal wind measure and the NAM approach but does not examine the vortex structure. It incorporates significant atmospheric forcings, called external factors, that play an important role in the wintertime evolution of the polar stratosphere. These externals factors are the quasi-biennial oscillation (QBO; e.g., Holton and Tan 1980 , 1982 ), the El Niño–Southern Oscillation (ENSO; e.g., Manzini et al. 2006

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L-L. Pan, F-F. Jin, and M. Watanabe

1. Introduction In the extratropics, atmospheric variability is dominated by abundant transient synoptic eddies. Embedded in such a turbulent circulation, there are prominent recurring patterns such as the Arctic Oscillation (AO) ( Thompson and Wallace 1998 , 2000 ) or North Atlantic Oscillation (NAO) ( Wallace and Gutzler 1981 ; Hurrell 1995 ; Wallace 2000 ), Antarctic Oscillation (AAO) ( Gong and Wang 1999 ; Thompson and Wallace 2000 ), and Pacific–North American (PNA) pattern ( Wallace

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François Lott, Andrew W. Robertson, and Michael Ghil

, rather than just via forcing the quasi-stationary planetary waves, it is necessary to establish statistically significant and physically coherent links between the mountain torques and the dominant patterns of extratropical LFV. In this perspective we emphasize in our results the mountain torque signals that precede changes of well-known LFV patterns, like the Arctic Oscillation ( Thompson and Wallace 1998 ; Wallace 2000 ). Conversely, our observational study also addresses the way that large

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William J. Randel, Fei Wu, Samuel J. Oltmans, Karen Rosenlof, and Gerald E. Nedoluha

the observed water vapor changes and temperatures near the tropical tropopause. We include some comparisons between the HALOE data and Polar Ozone and Aerosol Measurement (POAM) III measurements of water vapor in the Arctic stratosphere during 1998–2003. These two satellite datasets show good agreement for interannual changes during the overlap period, and this supports reliability of the global changes observed by HALOE. We also include comparisons between the HALOE data and updated time series

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James S. Risbey, Terence J. O’Kane, Didier P. Monselesan, Christian Franzke, and Illia Horenko

) ( Wallace and Gutzler 1981 ; Hurrell 1995 ), the Pacific–North America pattern (PNA) ( Wallace and Gutzler 1981 ), and a range of other structures. It has been argued that these regional structures may be manifestations of hemispheric-scale patterns, such as the Arctic Oscillation (AO) ( Lorenz 1951 ; Thompson and Wallace 1998 ). Some of the patterns, such as the PNA, exhibit wavelike characteristics and may also be related to a circumglobal waveguide pattern (CWP) ( Branstator 2002 ). Various methods

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Rafail Abramov, Andrew Majda, and Richard Kleeman

1. Introduction The successful prediction of low-frequency variability over the Northern Hemisphere on monthly to seasonal time scales depends on the ability to diagnose the temporal evolution of large-scale persistent teleconnection patterns, including the Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and Pacific–North American pattern (PNA). It has been demonstrated that many of the main features of low-frequency variability can be captured in barotropic models despite their

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Jinlong Huang and Wenshou Tian

CAOs. Various factors affecting the Eurasian CAOs have been reported in previous studies: for example, the Siberian high, the Arctic Oscillation (AO), El Niño–Southern Oscillation (ENSO), and Madden–Julian oscillation (MJO). Ding (1987) pointed out that the strengthened Siberian high corresponds well to an increase in the possibility of East Asian CAOs. Park et al. (2011) found that weaker Siberian high and Aleutian low could lead to shorter duration of East Asian CAOs, and negative AO phase is

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John M. Peters, Sergey Kravtsov, and Nicholas T. Schwartz

streamfunction. The streamfunction patterns associated with the leading EOFs of the zonal wind have a pronounced zonally symmetric component and describe a combination of north/south displacements and intensification/weakening of the zonal-mean zonal jet. This variability is often referred to as being associated with the Arctic Oscillation (AO) teleconnection pattern ( Thompson and Wallace 1998 ). The leading EOF of the zonal wind ( Fig. 1a ) is very similar to that of the streamfunction ( Fig. 1c ), but the

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Christian Franzke, Andrew J. Majda, and Eric Vanden-Eijnden

( Fig. 2a ). This pattern bears resemblance to the Arctic Oscillation/Northern Hemisphere Annular Mode (AO/NAM) ( Thompson and Wallace 1998 ). This pattern explains about 14% of the total variance. The second EOF pattern is displayed in Fig. 2b and resembles qualitatively the Pacific/North America (PNA) pattern ( Wallace and Gutzler 1981 ). It consists of a meridional dipole over the Pacific Ocean at the end of the Pacific subtropical jet and two further centers of action over Canada and Florida

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François Lott, Andrew W. Robertson, and Michael Ghil

, furthermore, between the Himalayas torque and ATL PC-2, which captures the evolution of the NAO; the torque and the PC are in quadrature (not shown). It is consistent with the NH mountain torque and NH PC-2 being in quadrature (see Part I) because the Himalayas torque makes a substantial contribution to the NH torque and because ATL EOF-2 (the NAO) is the sectorial component of the NH EOF-2 (the Arctic Oscillation; see section 2b ). The Himalayas also seem to have some downstream influence on the PAC EOF

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