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Judith Berner

dynamically interesting feature in PC4. The ACF of the GCM shows a dip for lags of 10 to 12 days. Since the ACF is still positive, this feature cannot be explained by a simple oscillation. The stochastic model does not capture this dip; however, it reproduces the overall decay rate up to lags of 75 days very well. Thus, the ACF of the stochastic model can be seen as an upper envelope for the ACF in the GCM. Since the decorrelation times are directly linked to the damped component of the drift and the

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R. S. Quiroz

Abstract

Radiance measurements made by the Satellite Infrared Spectrometers (SIRS A and B) and Vertical Temperature Profile Radiometers (VTPR) in 1969–74 comprise a basically uniform observational data source, in view of the similarity of the transmittance weighting functions for the stratospheric channels of these instruments. Hemispheric radiance maps of measurements in the 669 and 678 cm−1 channels are used to depict the evolution of major stratospheric warmings in the 1969–70, 1970–71 and 1972–73 winters. These warnings are indicated to have arisen from the interaction of eastward-travelling thermal waves with a standing wave in eastern Siberia. Sudden warming in the Arctic was related to the poleward migration of the resultant thermal systems. In these events the arctic mean stratospheric temperature increased by about 30°C in 8 days, but local increases were at least twice as great in the upper (196–70 and 1970–71) or middle (1972–73) stratosphere. The polar vortex breakdown is illustrated with the aid of conventional 10-mb map analyses and 2-mb data based on isobaric layer thicknesses derived from the radiance maps. A preliminary description of a late winter warming in 1973–74 is also given. Radiance patterns associated with minor and major events are distinguished, and during the 1973–74 winter both types are described within the context of repeating oscillations in the thermal structure. In all cases observed, major warmings were associated with the occurrence of horizontal radiance gradients of 15 mW (m2sr cm−1) (10°lat)−1 in both radiation channels.

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Liqi Chen, Wei Li, Jianqiong Zhan, Jianjun Wang, Yuanhui Zhang, and Xulin Yang

Atlantic Oscillation (NAO). The potential source regions for the two sites were different: Alert is usually under the influence of transport from Siberia and Europe, while Barrow showed influence from Siberian and Pacific–Asian transport. Pollutants from these geographical regions have declined since early 1990s owing to the decreased emissions in these source regions ( Quinn et al. 2011 ); therefore, their contribution to the aerosol loading in the Arctic has declined as well ( Hirdman et al. 2010

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Matthew D. Flournoy, Steven B. Feldstein, Sukyoung Lee, and Eugene E. Clothiaux

.1175/1520-0493(2004)132<1917:AARMMI>2.0.CO;2 . Yoo , C. , S. Feldstein , and S. Lee , 2011 : The impact of the Madden–Julian Oscillation trend on the Arctic amplification of surface air temperature during the 1979–2008 boreal winter . Geophys. Res. Lett. , 38 , L24804 , doi: 10.1029/2011GL049881 . Yoo , C. , S. Lee , and S. B. Feldstein , 2012a : Arctic response to an MJO-like tropical heating in an idealized GCM . J. Atmos. Sci. , 69 , 2379 – 2393 , doi: 10.1175/JAS-D-11-0261.1 . Yoo , C. , S. Lee

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Cory Baggett and Sukyoung Lee

four-box model of Cai (2005 , 2006) and its linear parameterization of the flux–gradient relationship. However, it is worth reiterating that we are comparing two processes that occur on vastly different time scales—climatic and subseasonal. In fact, recent studies have warned against the juxtaposition of these two time scales in the context of the Arctic Oscillation versus Arctic amplification ( Hassanzadeh et al. 2014 ; Hassanzadeh and Kuang 2015 ). These studies argued through modeling work

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S. Kravtsov, A. W. Robertson, and M. Ghil

annular modes ( Wallace 2000 ). The annular mode in the NH is called the Arctic Oscillation (AO; Deser 2000 ; Thompson and Wallace 2000 ; Thompson et al. 2000 ; Wallace 2000 ; Robertson 2001 ), while in the Southern Hemisphere (SH) it is known as zonal-flow vacillation ( Hartmann 1995 ; Hartmann and Lo 1998 ; Feldstein and Lee 1998 ; Lorenz and Hartmann 2001 ; Koo et al. 2003 ). Both modes stand out as the leading empirical orthogonal function (EOF) of data that are either low-pass filtered

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Shusaku Sugimoto and Kimio Hanawa

indices of four major teleconnection patterns: NAO, EA, TNH, and PNA ( Fig. 3 ). As expected, these maps ( Fig. 3 ) correspond well to those of WSC 1–WSC 4, respectively ( Fig. 2 ). In the Northern Hemisphere, it is known that the Arctic Oscillation (AO) is identified as a dominant EOF mode of sea level pressure ( Thompson and Wallace 1998 , 2000 ). Although the AO is considered not to be a teleconnection pattern, it might be expected that the AO forces the WSC variation in the North Atlantic. We

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Cory Baggett, Sukyoung Lee, and Steven Feldstein

. Res. Lett. , 33 , L03701 , doi: 10.1029/2005GL025244 . Woods , C. , R. Caballero , and G. Svensson , 2013 : Large-scale circulation associated with moisture intrusions into the Arctic during winter . Geophys. Res. Lett. , 40 , 4717 – 4721 , doi: 10.1002/grl.50912 . Yoo , C. , S. B. Feldstein , and S. Lee , 2011 : The impact of the Madden–Julian Oscillation trend on the Arctic amplification of surface air temperature during the 1979–2008 boreal winter . Geophys. Res. Lett

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Cory Baggett and Sukyoung Lee

1. Introduction A defining feature of warm equable paleoclimates is a reduction in their surface equator-to-pole temperature gradient ( Budyko and Izrael 1991 ; Hoffert and Covey 1992 ; Miller et al. 2010 ; Lee 2014 ). Similarly, a muted warming in the tropics and much greater warming in the Arctic characterize the present climate and observed twentieth-century trends ( Serreze and Barry 2011 ). Thus, when the Arctic receives little solar radiation, the Stefan–Boltzmann law implies (under

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G. B. Tucker and Jennifer M. Hopwood

relatively low level and implies that the amplitude continues to increase with increasing latitude untilwell within the Arctic Circle. The values of the amplitudes in the tropics are inagreement with results of a similar analysis by Shahand Godson (1966) for stations between 90N and 15S.They found that the oscillation became insign:[ficantpolewards of 25N. Figs. 6a and 6b show the total variance of the observations (full line) at each level at Hobart and Darwinand the percentage variance due to the

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