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Krzysztof M. Markowicz and Marcin L. Witek

cloudiness” ( Sausen et al. 2005 ). The climate effect in terms of the radiative forcing of contrail clouds is highly uncertain because of a limited number of observed statistics of contrail parameters (e.g., Palikonda et al. 2005 ) and difficulties with the parameterization of contrails in general circulation models ( Ponater et al. 2002 ; Rap et al. 2010 ; Kärcher et al. (2010) . The Intergovernmental Panel on Climate Change (IPCC) “Aviation and Global Atmosphere” special report ( Penner et al. 1999

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Jiapeng Miao, Tao Wang, Huijun Wang, Yali Zhu, and Jianqi Sun

. This is partly caused by suppressed ENSO-associated tropical Indo–western Pacific sea surface temperature (SST) variability, reduced EAWM interannual variability, and northward-retreating EAWM signals. The EAWM intensity is also regulated by the Arctic Oscillation (AO) on the interannual time scale ( Gong et al. 2001 ; Wu and Wang 2002 ). Furthermore, the Arctic amplification and sea ice loss may affect the EAWM ( Wang and Liu 2016 ; Zhou 2017 ). Both anthropogenic forcings [e.g., greenhouse

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Sarah D. Ditchek, John Molinari, and David Vollaro

composite nondeveloping storm with its diffuse eddy fluxes did not intensify. Most importantly, removing the eddy momentum fluxes from the developing storm prevented it from intensifying, even after 20 days. The authors hypothesized that a deep balanced response to these fluxes created enhanced radial circulation in the storm that contributed to its development. In this framework, outflow eddies provide meaningful forcing of tropical cyclone intensification. One limitation of the Pfeffer and Challa

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Haijun Yang and Lu Wang

the tropical ocean also tend to be shallow and symmetric to the equator under the symmetric extratropical forcing. Quantitative assessment of the extratropical impact on the tropical Atlantic has yet to be clarified. There are lots of observational and modeling studies on how the climate changes in the northern North Atlantic affect the tropical Atlantic ( Curry et al. 1998 ; Zhang and Delworth 2006 ; Sutton and Hodson 2007 ; Chang et al. 2008 ; Zhang et al. 2011 ). The thermal or freshwater

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Luis Gustavo G. de Goncalves, William J. Shuttleworth, Daniel Vila, Eliane Larroza, Marcus J. Bottino, Dirceu L. Herdies, Jose A. Aravequia, Joao G. Z. De Mattos, David L. Toll, Matthew Rodell, and Paul Houser

. 1996 ; Koster and Suarez 1999 ; Fennessey and Shukla 1999 ; Koster et al. 2004 ; de Goncalves et al. 2006a ), and that surface states such as soil moisture and temperature can affect atmospheric numerical model predictions. There are continuing efforts to increase the accuracy (and, as a result, complexity) of the representation within LSMs of the processes involved in the soil–vegetation–atmosphere system. However, realism can only ensue if LSMs are provided with realistic forcing data. Such

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Barbara Winter and Michel S. Bourqui

forcing in the polar vortex and thus an increased Brewer–Dobson circulation, with associated reduced vortex strength and higher temperatures in the polar lower stratosphere ( Rind et al. 1998 ; Sigmond et al. 2004 ; Braesicke and Pyle 2004 ; Butchart et al. 2006 ; Olsen et al. 2007 ; Winter and Bourqui 2010 ). The question has then been asked whether the stratosphere in such experiments is responding to the radiative effect of the increased greenhouse gas loading throughout the atmosphere or to

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Qigang Wu

dependent on lag and seasons. When SST leads Z500, about 80%–85% of the TSC is explained by the first MCA mode. The coupled patterns associated with the first MCA mode when SST and Z500 is assigned at DJF and JFM (not shown) indicate the forcing of atmosphere in the extratropics by the SST associated with conventional ENSO events in the tropical Pacific. The ENSO signature of extratropical atmospheric variability is very similar to that in the SVD analyses conducted between the seasonal mean Z500 and

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Tim Woollings, Abdel Hannachi, Brian Hoskins, and Andrew Turner

the mean flow forcing of transient eddies. As described by Ambaum et al. (2001) , it is clearly separated from the subtropical jet that is developing over the subtropical North Atlantic. On negative NAO days, in contrast, the two jet streams have merged to form one broad, continuous jet across the Atlantic. Several studies have suggested that these jet stream variations arise as a result of mean flow forcing associated with the breaking of transient, synoptic-scale Rossby waves (e.g., Benedict

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Ryan J. Kramer, Brian J. Soden, and Angeline G. Pendergrass

the surface radiative changes across models have received less attention. The forcing-feedback framework for understanding top-of-atmosphere (TOA) radiative changes (e.g., Sherwood et al. 2015 ) can also be applied to radiative changes at the surface ( Andrews et al. 2009 ; Colman 2015 ). A change in a forcing agent, such as CO 2 concentration, causes an instantaneous radiative perturbation at the surface, herein referred to as an instantaneous surface radiative forcing (ISRF). Rapid radiative

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Sarah M. Kang, Dargan M. W. Frierson, and Isaac M. Held

1. Introduction One of the most prominent features of the tropical climate is the intertropical convergence zone (ITCZ). Small changes in the structure and position of the ITCZ can produce large changes in local precipitation. Recent studies suggest that tropical precipitation can be influenced by extratropical forcing. For example, modeling studies show that the Atlantic ITCZ is displaced southward by freshwater input in the northern North Atlantic ( Stouffer et al. 2006 ; Zhang and Delworth

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