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

former two. Following Li et al. (2015) , we interpret these responses as a consequence of Rossby wave propagation; using a primitive equation solver ( Yoo et al. 2012 ) and Rossby wave tracing theory of Hoskins and Karoly (1981) , we then estimate the total Rossby wavenumber ( Ambrizzi et al. 1995 ) based on the climatological background state. Both the theoretical and the idealized model agree well with the realistic CAM4 simulation results, suggesting that the subtropical and midlatitude jets

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

gradient near the eddy-driven jet that perpetuates its displacement (e.g., Karoly 1990 ; Yu and Hartmann 1993 ; Hartmann and Lo 1998 ; Hall and Visbeck 2002 ; Rashid and Simmonds 2004 , 2005 ; Kidston et al. 2010 ). On intermediate time scales, thermal feedbacks between the ocean and atmosphere maintain SAM-induced anomalies of surface temperature and sea ice for weeks or months beyond the initial atmospheric signal ( Sen Gupta and England 2006 ; Ciasto and Thompson 2008 ). Late twentieth

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

relationships impact SH climate variability. We also examine how the two types of ENSO affect the relative importance of two mechanisms suggested to transmit ENSO forcing to high-latitude Southern Hemisphere: 1) an eddy–mean flow interaction mechanism in which an El Niño–induced intensification of the Hadley circulation and equatorward shift in the subtropical jet influence the propagation of midlatitude transient eddies and their associated eddy–mean flow interactions to give rise to a negative phase of

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David P. Schneider, Clara Deser, and Tingting Fan

1. Introduction One of the most discussed aspects of Southern Hemisphere (SH) climate change of the past several decades is the intensification and poleward shift of the midlatitude jet, reflected in stronger westerly winds between 50° and 70°S throughout the depth of the troposphere (e.g., Thompson et al. 2011 ; Previdi and Polvani 2014 ). This wind shift projects on the positive phase of the southern annular mode (SAM), which is commonly defined as the leading empirical orthogonal function

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Xiaojun Yuan, Michael R. Kaplan, and Mark A. Cane

al. 2002 ). Similarly, the atmospheric responses can be traced in the Northern Hemisphere (NH) extratropics ( Trenberth et al. 1998 ; Pozo-Vázquez et al. 2005 ; Cassou and Terray 2001 ; Jevrejeva et al. 2003 ). The mechanisms fostering the connection between ENSO and the high latitudes through the troposphere include 1) the Rossby waves generated by tropical convection ( Karoly 1989 ; Mo and Higgins 1998 ; Kiladis and Mo 1998 ; Garreaud and Battisti 1999 ); 2) jet stream changes in response

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Robert A. Tomas, Clara Deser, and Lantao Sun

; Sun et al. 2015 ) and an increase in warm extremes ( Screen et al. 2015b ) as a result of Arctic sea ice loss. In addition to local thermodynamic effects, diminished Arctic sea ice cover will weaken the tropospheric westerly winds along the poleward flank of the jet stream in association with a reduced north–south temperature gradient due to enhanced lower-tropospheric warming in the Arctic ( Deser et al. 2010 ; Peings and Magnusdottir 2014 ; Deser et al. 2015 , hereafter D15 ; Harvey et al

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Changhyun Yoo, Sungsu Park, Daehyun Kim, Jin-Ho Yoon, and Hye-Mi Kim

and the western Pacific. Sardeshmukh and Hoskins (1988) showed that for a barotropic atmosphere, the Rossby wave source ( S ) is a function of irrotational wind and absolute vorticity gradient ( ζ ), that is, . Because of the local maximum of absolute vorticity gradient, as well as the divergence anomalies associated with the MJO, the exit of the Asian jet is the key region for exciting poleward propagating Rossby waves associated with the MJO ( Adames and Wallace 2014 ). Thus, the minimal

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Bradley P. Goodwin, Ellen Mosley-Thompson, Aaron B. Wilson, Stacy E. Porter, and M. Roxana Sierra-Hernandez

recently (post 1998) it has trended toward a negative phase. The positive PDO exhibits more El Niño–like conditions that shift the SPCZ to the northeast (in response to contracted Hadley circulation and a stronger subtropical jet stream), limiting poleward-propagating synoptic eddy momentum fluxes that can increase cyclonic activity near the AP ( Chen et al. 1996 ). However, accumulation on the BP continued to increase during this period under the influence of the increasing SAM. Since 1999

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Graham R. Simpkins, Yannick Peings, and Gudrun Magnusdottir

descending branch by upper-level vorticity anomalies ( Simpkins et al. 2014 ). In both observations and models, the wave train promotes a significant deepening of the ASL in all seasons except austral summer, highlighting a seasonality to the teleconnection that is governed by the strength and extension of the subtropical jet ( Li et al. 2015a ). While geopotential height anomalies associated with Atlantic teleconnections are largely centered over the ASL, significant features are also observed over the

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Bradford S. Barrett, Gina R. Henderson, and Joshua S. Werling

the MJO and polar circulations . J. Climate , 26 , 3562 – 3574 , doi: 10.1175/JCLI-D-11-00508.1 . Francis , J. A. , and S. J. Vavrus , 2015 : Evidence for a wavier jet stream in response to rapid Arctic warming . Environ. Res. Lett. , 10 , 014005 , doi: 10.1088/1748-9326/10/1/014005 . Garfinkel , C. I. , J. J. Benedict , and E. D. Maloney , 2014 : Impact of the MJO on the boreal winter extratropical circulation . Geophys. Res. Lett. , 41 , 6055 – 6062 , doi: 10.1002/2014GL

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