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Ryan L. Fogt and Alex J. Wovrosh

extent changes in the region. In light of this ongoing area of research, the goal of this study is to more precisely understand the relative roles of tropical–extratropical sea surface temperature variations and radiative forcing in both the variability and changes in the ASL, specifically through multiple climate model simulations. The paper is laid out as follows: Section 2 details the various model simulations and reanalysis data utilized within this research, including several statistical

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Xiaofang Feng, Qinghua Ding, Liguang Wu, Charles Jones, Ian Baxter, Robert Tardif, Samantha Stevenson, Julien Emile-Geay, Jonathan Mitchell, Leila M. V. Carvalho, Huijun Wang, and Eric J. Steig

1. Introduction Global surface temperatures have been warming significantly in the past 40 years due to anthropogenic forcing associated with increases in greenhouse gases (e.g., Lacis et al. 2010 ). However, the warming over this time has exhibited a prominent asymmetry ( Maksym et al. 2012 ; Ji et al. 2014 ), characterized by strong warming in and around the Arctic with pronounced sea-ice and land-ice melting ( Serreze and Barry 2011 ; Vaughan et al. 2013 ), but slight cooling over the

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Aaron B. Wilson, David H. Bromwich, and Keith M. Hines

and thus the meridional variability of the circumpolar westerly winds. The SAM varies from daily ( Baldwin 2001 ) to interdecadal time scales ( Kidson 1999 ) and can occur without external forcing ( Limpasuvan and Hartmann 1999 , 2000 ). The persistence and internal variability of the SAM is the result of positive feedbacks between baroclinicity and the meridional propagation of high-frequency eddies in the upper levels of the atmosphere, such that the Ferrel cell maintains a strong thermal

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Kyle R. Clem, James A. Renwick, and James McGregor

Antarctica during winter and spring ( Steig et al. 2009 ; Ding et al. 2011 ; Schneider et al. 2012 ; Bromwich et al. 2013 ; Nicolas and Bromwich 2014 ). Apart from the warming on the northeast peninsula, the recent Antarctic Peninsula/West Antarctica climate trends lie within their respective ranges of internal variability and are likely tied to natural decadal variability in atmospheric circulation rather than anthropogenic forcing ( Jones et al. 2016a ; Turner et al. 2016 ). The western peninsula

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David P. Schneider, Clara Deser, and Tingting Fan

, resulting in a poleward shift of the jet ( Vallis et al. 2014 ). Apart from Staten et al. (2012) , the role of tropical SST forcing in the context of observed SH circulation trends has been interpreted in terms of poleward-propagating Rossby waves, which are associated with zonally asymmetric circulation patterns at middle and high latitudes. These waves, fueled by anomalous deep convection and latent heating in the tropics, are the main pathway of tropical–Antarctic linkages. Several studies

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Graham R. Simpkins, Yannick Peings, and Gudrun Magnusdottir

only the SST boundary conditions are modified: ATL3W , to assess the impact of positive (or warm) ATL3 events. For this experiment the pattern of monthly SST anomalies associated with ATL3, as determined through monthly regressions, is superimposed on the background climatology (see Fig. A1 for SST forcing). To avoid unrelated atmospheric responses beyond the regions of interest, the superimposed SST anomalies were constrained to the Atlantic and Pacific Oceans between 15°N and 25°S. Linear

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N. Fauchereau, B. Pohl, and A. Lorrey

which follows, has led to somewhat conflicting conclusions: Carvalho et al. (2005) indicate that the negative SAM phase onset is related to the propagation of the MJO. Suppression of intraseasonal convective activity over Indonesia is observed in positive SAM phases. Matthews and Meredith (2004) indicate that the Antarctic Circumpolar Current could respond to the MJO through changes in wind forcing (related to the SAM) in the SH high latitudes during the Southern Hemisphere winter. They indicate

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Jin-Yi Yu, Houk Paek, Eric S. Saltzman, and Tong Lee

Hartmann 2001 ). Forcing from the tropics, such as that associated with ENSO, is considered less important, although correlations can be found between SAM and ENSO in austral summer (e.g., Karoly 1989 ; Seager et al. 2003 ; Silvestri and Vera 2003 ; Zhou and Yu 2004 ; Codron 2005 ; L’Heureux and Thompson 2006 ). The PSA is characterized by a stationary Rossby wave train emanating from the tropical central Pacific with major anomaly centers to the east of New Zealand, in the Amundsen

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Xichen Li, David M. Holland, Edwin P. Gerber, and Changhyun Yoo

play a key role in channeling wave activity from the Atlantic and Pacific to West Antarctica. The outline of this paper is as follows: The tropical SST trend is estimated in section 2 , which is then used to force the atmospheric models. Results from the CAM4 comprehensive atmospheric model simulations are presented in section 3 , followed by results from the GFDL dry-dynamical core simulations in section 4 , and those from the theoretical model in section 5 . Conclusions are drawn in section

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Ariaan Purich, Matthew H. England, Wenju Cai, Yoshimitsu Chikamoto, Axel Timmermann, John C. Fyfe, Leela Frankcombe, Gerald A. Meehl, and Julie M. Arblaster

since 1979 can be explained by interdecadal variability ( Fan et al. 2014 ; Gagné et al. 2015 ), particularly arising from the phase change of the interdecadal Pacific oscillation (IPO) to negative after the late 1990s ( Meehl et al. 2016a ), rather than by direct anthropogenic forcing. As such, it is pertinent to scrutinize the proposed causes of these trends. Here we further examine the concept that recent trends in tropical SST and tropical-to-extratropical teleconnections influenced the

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