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Yueyue Yu, Rongcai Ren, Jinggao Hu, and Guoxiong Wu

1. Introduction Climate variability of Arctic surface pressure (Ps) is intimately related to the leading recurrent oscillation modes in the northern extratropics, namely the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) ( Kuroda 2005 ) and the northern annular mode (NAM) ( Lorenz 1951 ; Kodera et al. 1990 ; Thompson and Wallace 1998 ; Baldwin and Dunkerton 1999 ; Baldwin 2001 ). The positive (negative) phase of AO/NAM is characterized with a decrease (increase) in polar Ps

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Pablo Zurita-Gotor

Abstract

Friction is an important parameter in atmospheric modeling that may affect internal variability in a number of ways. It directly damps the annular-mode variability, but it also helps to maintain it through baroclinic feedbacks. Also, by determining the mean strength and position of the midlatitude jet, friction affects the internal dynamics that drive this variability. This work investigates the relevance of all of these factors for the sensitivity of the persistence of annular variability to changes in the zonal-mean friction using an idealized quasigeostrophic two-layer model. This model produces realistic variability, yet it is so simple that one can cleanly separate the different effects. It is found that the sensitivity of persistence to friction is dominated by the direct damping effect, while changes in the eddy momentum forcing and in the mean jet are not as important.

As in more complex models, the persistence of the jet anomalies in this model decreases at all lags with increasing friction, but the long-time decorrelation decay rate of these anomalies is remarkably insensitive to friction. Although this implies that the eddy feedback must increase with friction to maintain the anomalies against the enhanced damping, it is shown that this is not due to baroclinic effects. A model that assumes that the eddy forcing does not change with friction can reproduce reasonably well the numerical results. The crucial factor that determines the model’s sensitivity to friction is the spectral structure of the eddy momentum forcing.

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Changhyun Yoo, Sukyoung Lee, and Steven B. Feldstein

numerical model outputs . Bull. Amer. Meteor. Soc. , 78 , 2539 – 2558 . 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. Feldstein , 2012 : Mechanisms of Arctic surface air temperature change in response to the Madden–Julian oscillation . J. Climate

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Ralph Shapiro and Harold L. Stolov

pressure at arctic and antarcticstations along with various measures of solar variability, such as f~in, riometer data, and Kp, failed toreveal any associations between solar particle emission and the surface pressure in polar regions. However,a small but apparently real coherent variation in surface pressure exists between the two polar regions.This oscillation with period somewhat greater than 60 days is almost exactly 180- out of phase between thetwo polar regions, indicating a more or less direct

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Renqiang Liu and Yanyan Fu

applying suitable boundary conditions and neglecting the eddy momentum flux forcing term at the reference latitude. The main difference is that Hu and Tung (2002) did not treat the diabatic heating term but Newman et al. (2001) had approximated it as the standard Newtonian cooling approximation ( Fels 1982 ) and argued that the preceding wave driving will have limited impact on the current temperature. While both approximate equations may be applicable to the study on the Arctic lower

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Kyong-Hwan Seo, Hyun-Ju Lee, and Dargan M. W. Frierson

), El Niño ( Zavala-Garay et al. 2005 ; McPhaden 1999 ), the Pacific–North America pattern, Arctic Oscillation or North Atlantic Oscillation (e.g., Zhou and Miller 2005 ; Cassou 2008 ; L’Heureux and Higgins 2008 ; Lin et al. 2009 ; Riddle et al. 2013 ), the jet streams (e.g., Matthews et al. 2004 ; Seo and Son 2012 ), and pineapple express or atmospheric river events (e.g., Kerr 2006 ). Recently, Yoo et al. (2012a) demonstrated that MJO-induced Rossby wave propagation contributes to

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D. Kondrashov, S. Kravtsov, and M. Ghil

represent, in physical space, the patterns of four planetary flow regimes ( Legras and Ghil 1985 ; Ghil and Childress 1987 , chapter 6; Mo and Ghil 1988 ; Cheng and Wallace 1993 ; Kimoto and Ghil 1993a , b ; Hannachi 1997 ; Smyth et al. 1999 ; Hannachi and O'Neill 2001 ; Molteni 2002 ). These regimes are associated with the opposite phases of the NH annular mode, the so-called Arctic Oscillation (AO; Deser 2000 ; Thompson and Wallace 2000 ; Thompson et al. 2000 ; Wallace 2000 ), and the

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Murry L. Salby

cold winters by its relationship to isentropic surfaces ( Salby and Callaghan 2007 ). The climate sensitivity of temperature has structure very similar to that associated with the Arctic Oscillation ( Thompson and Wallace 2000 ). Out of phase between high and low latitudes, each form of interannual variability bears the signature of the residual mean circulation. The numerical integrations, in which anomalous temperature is formally linked to residual motion, make its involvement explicit. The

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F-F. Jin, L-L. Pan, and M. Watanabe

) atmospheric variability is the North Atlantic Oscillation (NAO) ( Walker and Bliss 1932 ; van Loon and Rogers 1978 ; Hurrell 1995 ; Hurrell et al. 2003 ). The NAO is also considered as a part of the global-scale pattern known as the Arctic Oscillation (AO) or the NH annular mode (NAM; Thompson and Wallace 1998 , 2000 ; Wallace 2000 ). Another well-known recurrent pattern of the NH atmospheric variability is the so-called Pacific–North American (PNA) pattern ( Wallace and Gutzler 1981 ). The

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D. Kondrashov, K. Ide, and M. Ghil

circulation are most often identified as the Pacific–North American (PNA) pattern, the reverse PNA (RNA), the North Atlantic Oscillation (NAO), and the Arctic Oscillation (AO). The positive and negative phases of the NAO correspond to zonal and blocked flow in the Atlantic sector, in the same way the PNA and RNA do so over the Pacific sector of the NH. The AO ( Thompson and Wallace 1998 ; Wallace 2000 ) is a hemispheric, annular mode that has been strongly associated with the sectorial NAO. Marshall and

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