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Lars Gerlitz, Eva Steirou, Christoph Schneider, Vincent Moron, Sergiy Vorogushyn, and Bruno Merz

significance and spurious correlations. Thus, the influence of large-scale atmospheric modes on the regional-scale circulation and the underlying atmospheric processes linking remote teleconnection indices with observed climate anomalies are often not well understood ( Lee 2017 ). The analysis of discrete weather types (WT), representing an intermediate scale between the large-scale circulation and the regional climatology, has been used to address this physical link for various target regions (e

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Wilbur Y. Chen

the present model. However, the gross resemblance of the variability pattern with observations provides us an opportunity to examine further the modification of its natural variability while its mean flow undergoes a change from an El Niño to a La Niña type. 4. Simulation of the extratropical mean response to tropical anomalous forcing Before examining the changes in natural variability, we would like to get a feel as to how close the model mean response is to the anomalous tropical forcing, as

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Eric E. Small, Lisa Cirbus Sloan, and Doug Nychka

1. Introduction In order to understand why climate changes through time, it is critical to establish cause–effect relationships between certain forcings of the climate system, both anthropogenic and natural, and different components of observed climatic changes. Local or regional climate may change as a result of spatially restricted anthropogenic modifications of the land surface, including deforestation, irrigation, urbanization, and desiccation of inland water bodies. Establishing the

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A. Hannachi

surface boundary conditions such as SST anomalies. Many works have been devoted to identifying such persistent or quasi-stationary patterns or weather regimes, to analyzing the main sources of their maintenance by studying the corresponding high-frequency transient eddies, and to a lesser extent, to the study of their mutual transitions, onsets, and breaks. For example, Rex (1950) and Namias (1964) were the first to notice that blocking, considered as a regional persistent weather pattern ( Dole

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David J. Travis, Andrew M. Carleton, and Ryan G. Lauritsen

of contrail radiative forcing. Geophys. Res. Lett , 26 , 1853 – 1856 . Minnis , P. , L. Nguyen , D. P. Duda , and R. Palikonda , 2002 : Spreading of isolated contrails during the 2001 air traffic shutdown. Preprints, 10th Conf. on Aviation, Range, and Aerospace Meteorology, Portland, OR, Amer. Meteor. Soc., 33–36 . Murcray , W. B. , 1970 : On the possibility of weather modification by aircraft contrails. Mon. Wea. Rev , 98 , 745 – 748 . NCDC , 2003 : Data

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James E. Overland and Muyin Wang

and subarctic atmospheric circulation. Firm attribution of recent increased circulation variance is not possible ( Trenberth et al. 2015 ). 2. Recent subarctic weather in North America Based on Fig. 1 we focus on the variability of circulation in recent Decembers ( Table 1 ). The historical mean 700-hPa geopotential height pattern is shown in Fig. 2a and the composite height anomaly patterns for the three recent major negative AO (−AO) events (2009, 2010, 2012) and three positive AO (+AO

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Qing Liu and Cornelius J. F. Schuurmans

agrees well with the results of correspondinggeneral circulation model (GCM) experiments. For a heating at the date line, the modification of the linearresponse by the nonlinear terms is substantial. The nonlinear response to the heating is much stronger than thelinear response, whereas the nonlinear response to cooling is weaker. The main effect oftbe nonlinear terms isto modify the amplitudes; the structure of the response is only slightly adjusted. Both the linear and the nonlinearsteady

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Andrew Hoell and Chris Funk

1. Introduction El Niño–Southern Oscillation (ENSO) extremes have been linked to global climate modifications (e.g., Ropelewski and Halpert 1987 , 1989 ; Trenberth et al. 1998 ; Diaz et al. 2001 ) and substantial precipitation impacts over portions of the United States (e.g., Ropelewski and Halpert 1986 ; McCabe and Dettinger 2002 ), southwest Asia ( Barlow et al. 2002 ; Mariotti 2007 ; Syed et al. 2006 , 2010 ), and eastern Africa ( Farmer 1988 ; Indeje et al. 2000 ; Camberlin et al

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Chung-Chun Ma, Carlos R. Mechoso, Akio Arakawa, and John D. Farrara

parameterization for the adjustment of the cloud work function (CWF), which is a measure of. moist-convectiveinstability, to its quasi-equilibrium value specified foreach cloud type. For a given difference of the CWFfrom the quasi-equilibrium value, this modification reduces the mass flux and, therefore, the tendency ofcumulus convection to restore the quasi-equilibriumcondition. After a Consecutive sequence of these "relaxed adjustments" under a constant forcing from thelarge-scale, environment, the

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Larry W. O'Neill, Dudley B. Chelton, and Steven K. Esbensen

of Jury (1994) are consistent with the secondary circulations and the associated pressure distribution found in the Wai and Stage (1989) and Warner et al. (1990) models. Satellite observations in the tropical Pacific have documented the relationship between SST and surface winds in much greater detail than has been possible from ship-based observations. As SST modification of surface winds has been studied more extensively in the tropical Pacific than at midlatitudes, we highlight here some

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