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Paul C. Loikith and Anthony J. Broccoli

(NAM), also referred to as the Arctic Oscillation, is characterized by an annular structure of latitudinally stratified geopotential height anomalies of opposing sign with one band at high northern latitudes and the other over the midlatitudes. When the NAM is in the positive phase, the midlatitude westerlies are anomalously strong, inhibiting the southward penetration of surges of cold air into the continental United States. This corresponds to anomalously warm temperatures in the midlatitudes and

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Alexander R. Stine and Peter Huybers

, doi:10.1029/2007GL030891 . Baldwin , M. , and T. Dunkerton , 1999 : Propagation of the Arctic Oscillation from the stratosphere to the troposphere . J. Geophys. Res. , 104 ( D24 ), 30 937 – 30 946 . Baldwin , M. , X. Cheng , and T. Dunkerton , 1994 : Observed correlations between winter-mean tropospheric and stratospheric circulation anomalies . Geophys. Res. Lett. , 21 , 1141 – 1144 . Baldwin , M. , D. Stephenson , D. Thompson , T. Dunkerton , A. Charlton

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Chaim I. Garfinkel and Darryn W. Waugh

., 117, D13115 , doi: 10.1029/2012JD017597 . Wittman , M. A. H. , L. M. Polvani , R. K. Scott , and A. J. Charlton , 2004 : Stratospheric influence on baroclinic lifecycles and its connection to the Arctic Oscillation . Geophys. Res. Lett. , 31, L16113 , doi: 10.1029/2004GL020503 . Wittman , M. A. H. , A. J. Charlton , and L. M. Polvani , 2007 : The effect of lower stratospheric shear on baroclinic instability. J. Atmos. Sci., 64, 479–496 , doi: 10.1175/JAS3828

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Jacob Coburn and S. C. Pryor

. 2016 ), and the Atlantic multidecadal oscillation (AMO) ( Deser et al. 2010 ) ( Fig. 1 ). Fig . 1. Schematic of the locations of the major climate modes assessed in this work. The atmospheric modes—the northern annular mode (NAM; or Arctic Oscillation), southern annular mode (SAM; or Antarctic Oscillation), and Pacific–North American pattern (PNA)—are shown in italics. The oceanic modes—the Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and El Niño–Southern Oscillation

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Irina Rudeva and Ian Simmonds

quasi-stationary Rossby waves (e.g., Luo et al. 2018 ; D. Luo et al. 2019 ; Xie et al. 2020 ). A number of dynamical phenomena known to encourage Arctic–midlatitude connections are intimately related to the changes in this gradient, which is reduced following amplified warming in the Arctic. For example, changes in the storm track through a shift in the North Atlantic Oscillation (NAO)/Arctic Oscillation ( Rudeva and Simmonds 2015 ; Luo et al. 2016 ; Vihma et al. 2020 ), weakening of the polar

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Erik W. Kolstad, Stefan P. Sobolowski, and Adam A. Scaife

and European surface climate have been linked to Arctic sea ice variability (e.g., Yang and Christensen 2012 ; Liptak and Strong 2014 ), Eurasian snow cover (e.g., Cohen and Entekhabi 1999 ), and tropical phenomena such as the Madden–Julian oscillation (e.g., Cassou 2008 ) and El Niño events (e.g., Toniazzo and Scaife 2006 ). On longer time scales, slowly varying North Atlantic sea surface temperature (SST) fluctuations also yield predictability ( Keenlyside et al. 2008 ). The assumption is

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Peter A. Bieniek, John E. Walsh, Richard L. Thoman, and Uma S. Bhatt

time ( Robock 1984 ). However, no such depression of Alaskan temperatures is apparent in Fig. 4 following the larger eruption of Mt. Pinatubo in 1991, and there were no known major eruptions preceding the downward excursion of the divisional temperatures in the 1930s. The depression of temperatures in the early 1980s may have been associated with the prevailing positive phase of the Arctic Oscillation, which is associated with below-normal temperatures in Alaska. An impact of a volcanic eruption

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Hua Lu, Lesley J. Gray, Patrick Martineau, John C. King, and Thomas J. Bracegirdle

stratosphere, the NAM characterizes variations in the strength of the polar vortex, with a positive NAM indicating a stronger-than-average vortex. In the troposphere, the NAM is also called the Arctic Oscillation (AO), which primarily characterizes meridional shifts in the extratropical westerly jets, with a positive AO indicating a poleward shift ( Thompson and Wallace 1998 ). The NAM (and the tropospheric AO) is primarily associated with the geopotential height over the polar cap ( Baldwin and Thompson

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Philip R. Thompson, Gary T. Mitchum, Cedric Vonesch, and Jianke Li

increase in storm frequency over GOM and East Coast marine areas from the 1910s through the 1970s with a peak in the 1960s, which is consistent with our results. The winter of 2009/10 in the southeast United States was characterized by record cold temperatures and snowfall associated with multiple winter storms. The severe winter in the region was due in part to an extreme negative phase of the Arctic Oscillation and the associated northward redistribution of atmospheric mass ( Cohen et al. 2010 ). We

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Mira Berdahl, Asa Rennermalm, Arno Hammann, John Mioduszweski, Sultan Hameed, Marco Tedesco, Julienne Stroeve, Thomas Mote, Tomoko Koyama, and Joseph R. McConnell

. 2006 ). There have been a handful of studies relating Greenland precipitation to the NAO (e.g., Mosley-Thompson et al. 2005 ; Bromwich et al. 1999 ; Appenzeller et al. 1998a ; Appenzeller et al. 1998b ), showing that the NAO most strongly modulates precipitation in western and southern Greenland during winter. Other teleconnection indices characterizing climate in the North Atlantic region, and Greenland in particular, are the Arctic Oscillation (AO), the Atlantic multidecadal oscillation (AMO

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