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Alan Condron, Peter Winsor, Chris Hill, and Dimitris Menemenlis

Gerdes 2007 ). The atmospheric circulation of the Arctic is dominated by the North Atlantic Oscillation(NAO)/Arctic Oscillation (AO) ( Hurrell 1995 ; Thompson and Wallace 1998 ), which switched from its most extreme negative state in the 1960s to its most extreme prolonged positive state in the early 1990s ( Fig. 1a ). 1 Häkkinen and Proshutinsky (2004) and Köberle and Gerdes (2007) both simulated the Arctic freshwater budget from the 1950s to the early 2000s using two different coupled ocean

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Lei Cai, Vladimir A. Alexeev, John E. Walsh, and Uma S. Bhatt

1. Introduction Two leading modes—the Arctic Oscillation (AO) and the Arctic dipole (AD)—contribute the most to the large-scale atmospheric circulation over the Arctic in summer [June–August (JJA)]. By definition, both modes of variability are derived from applying empirical orthogonal function (EOF) analysis to the sea level pressure (SLP) anomaly field. The first EOF mode represents the AO that dominates the atmospheric circulation over the Arctic ( Thompson and Wallace 1998 ; Wu et al. 2006

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Ian Simmonds, Craig Burke, and Kevin Keay

of temporal variability with oscillations with periods of up to 60–80 yr (often superimposed on trends) showing up in many of the variables. A number of conceptual models based on the range of feedbacks that are present in the complex Arctic atmospheric, oceanic, and cryospheric domain have been proposed to account for the spectrum of variabilities (e.g., Mysak and Venegas 1998 ; Gudkovich and Kovalev 2002 ; Wang et al. 2005 ; Overland and Wang 2005 ). Notwithstanding the difficulties and

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James Morison, Ron Kwok, Suzanne Dickinson, Roger Andersen, Cecilia Peralta-Ferriz, David Morison, Ignatius Rigor, Sarah Dewey, and John Guthrie

1. Introduction Present Arctic Ocean near-surface circulation is commonly characterized as being in an anticyclonic phase ( Hofmann et al. 2015 ; McPhee et al. 2009 ; Proshutinsky et al. 2015 , 2009 ). This idea is largely based on in situ observations in the Canada Basin that are biased toward measuring the intensity of the anticyclonic Beaufort Gyre and on a regional index of Arctic Ocean circulation, the Arctic Ocean Oscillation index (AOOI). The AOOI is the sea surface height gradient

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David W. Stahle, Edward R. Cook, Dorian J. Burnette, Max C. A. Torbenson, Ian M. Howard, Daniel Griffin, Jose Villanueva Diaz, Benjamin I. Cook, A. Park Williams, Emma Watson, David J. Sauchyn, Neil Pederson, Connie A. Woodhouse, Gregory T. Pederson, David Meko, Bethany Coulthard, and Christopher J. Crawford

, but the NAO teleconnection to instrumental and reconstructed DJFMA precipitation also weakened during the earliest period of instrumental GPCC precipitation observations from 1892 to 1927 (not shown). The Arctic Oscillation (AO) is an annular mode of zonal circulation between 35° and 55°N ( Ambaum et al. 2001 ). The NAO and PNA are related to the AO ( Ambaum et al. 2001 ), and the correlation between indices of the NAO and AO for the winter to midspring season (DJFMA) is r = 0.68 ( p < 0

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R. W. Higgins, V. B. S. Silva, W. Shi, and J. Larson

PDO on precipitation (specifically the frequency of extreme daily rainfall) over the contiguous United States is largely through its modulation of ENSO. The circulations of both hemispheres exhibit important ring-like (or annular) modes of variability encircling the poles that fluctuate on time scales ranging from a week to decades (e.g., Thompson and Wallace 2000 ). The Northern Hemisphere annular mode, often referred to as the Arctic Oscillation (AO) ( Thompson and Wallace 1998 ), is marked by

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Asgeir Sorteberg and Børge Kvingedal

the second half of the twentieth century. McCabe et al. (2001) showed that high-latitude cyclone frequencies correlate well (0.69) with the Arctic Oscillation (AO), which is the dominant pattern of sea level pressure (SLP) variations north of 20°N ( Thompson and Wallace 1998 ) over the 1959–97 period. Many studies have focused on the connection between Arctic sea ice variability and the AO or the North Atlantic Oscillation (NAO; Hurrell 1995 ), which essentially describes the same airmass

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Courtenay Strong and Robert E. Davis

circulation variability has also been described in the context of a more hemispheric seesaw of atmospheric mass known as the Arctic Oscillation (AO) ( Thompson and Wallace 1998 ), the leading empirical orthogonal function (EOF) of sea level pressure poleward of 20°N. The AO partially overlaps the NAO in the Atlantic but features a zonally symmetric structure over the Pacific, covers more of the Arctic, and is discernible in geopotential height fields from the troposphere into the lower stratosphere

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Yuefeng Li and L. Ruby Leung

temperature and rainfall in the Yangtze and Huai Rivers and an increase of rainfall in southeastern China ( Zhao et al. 2007 ). More recently, the relationships between the Asian summer monsoon anomalies and the Arctic have become active research topics. However, our understanding of the causes and effects of the anomalies is far from complete. A few papers have investigated the influence of the Arctic ice concentration ( B.-Y. Wu et al. 2009a , b ) and the Arctic Oscillation (AO) on the East Asian summer

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Lejiang Yu, Shiyuan Zhong, Mingyu Zhou, Donald H. Lenschow, and Bo Sun

. 2015 ) have contributed to the decrease in the Arctic sea ice extent. Besides the increased greenhouse gas emissions, natural variability of the climate system may have also contributed to the Arctic sea ice depletion. The downward trend of the Arctic sea ice prior to the 1990s has been linked to a positive trend in the North Atlantic Oscillation (NAO) index ( Deser et al. 2000 ), and this linkage is expected to extend into the first decade of the twenty-first century ( Ogi et al. 2010 ). The

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