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Jan Kretzschmar, Marc Salzmann, Johannes Mülmenstädt, Olivier Boucher, and Johannes Quaas

1. Introduction Quantitative understanding of climate change during the industrial era suffers from a highly uncertain effective radiative forcing (radiative forcing plus adjustments) due to anthropogenic aerosols, ( Boucher et al. 2013 ). Stevens (2015 , hereinafter S15) proposed that the temporal and spatial characteristics of the observed warming since preindustrial times provide a powerful constraint on the total anthropogenic aerosol forcing. We follow S15 and assume that warming

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Jeongbin Seo, Sarah M. Kang, and Dargan M. W. Frierson

1. Introduction Much of the precipitation in the tropics occurs within a narrow zonal band of high rainfall known as the intertropical convergence zone (ITCZ). Because small changes in the position of the ITCZ can greatly perturb local precipitation, it is important to understand how the ITCZ may respond to external thermal forcing. While the ITCZ is often thought to be controlled by tropical mechanisms (e.g., Xie 2004 ), recent studies that have demonstrated that the ITCZ can respond to

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Nathaniel B. Miller, Matthew D. Shupe, Christopher J. Cox, Von P. Walden, David D. Turner, and Konrad Steffen

the net radiative flux at the surface ( Walsh and Chapman 1998 ), thereby impacting the surface energy budget. The shortwave and longwave radiative effect of clouds, or cloud radiative forcing (CRF), can be quantified by comparing the actual surface radiative flux to the flux during an equivalent clear-sky scene. In general, Arctic clouds have a warming effect on the surface, except for a period in the summer when the sun is highest and surface albedo is lowest ( Curry and Ebert 1992 ; Intrieri

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Rongcai Ren, Xin Xia, and Jian Rao

using simple models to perform idealized numerical experiments, early investigators identified the important dynamical roles of topographic forcing in modulating the stratosphere. For example, early simulations by Manabe and Terpstra (1974) indicated that topographic forcing serves to amplify the amplitudes of the stratospheric planetary waves of very low wavenumber, by transporting energy from the troposphere to the stratosphere. Later studies further demonstrated the varying dynamical roles of

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Karen L. Smith, Christopher G. Fletcher, and Paul J. Kushner

character and because they are modulated by multiple influences, including interactions with the ocean surface, the land surface, and the stratosphere ( DeWeaver and Nigam 2004 ; Limpasuvan and Hartmann 2000 ; Czaja and Frankignoul 2002 ; Gong et al. 2002 ; Baldwin et al. 2003 ). In simulations, the response of the modes to a prescribed forcing is model dependent because many details, including the characteristics of the modes, the temporal and spatial structure of the forcing, the background flow

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Clara Deser and Adam S. Phillips

; Trenberth and Hurrell 1994 ; Deser et al. 2004 ). The latter may also play a contributing role to circulation trends over the North Atlantic ( Hoerling et al. 2004 ; Hurrell et al. 2004 ), although intrinsic variability due to nonlinear atmospheric dynamics is also important ( Schneider et al. 2003 ; Hurrell et al. 2004 ; Bracco et al. 2004 ). Thus, there is evidence that both SST changes and atmospheric radiative forcing due to changes in greenhouse gas and ozone concentrations have contributed to

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Zhili Wang, Junyu Mu, Meilin Yang, and Xiaochao Yu

forcing has been identified as a primary driver of long-term changes in the East Asian summer monsoon (EASM) since the 1950s ( Song et al. 2014 ; Liu et al. 2019 ). Several studies showed different impacts of aerosol forcing on the monsoon system through a regional climate model approach (e.g., Ji et al. 2011 ; Zhuang et al. 2018 ) compared to the results from a global climate model because of the high resolution and lack of nonlocal aerosol effects. Aerosols emitted from local sources generally

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Shayne McGregor, Neil J. Holbrook, and Scott B. Power

. (2003a , b ) went one step further and combined off-equatorial wind stress forcing with ENSO theory to produce a unified theory for decadal variability and ENSO modes. However, the manner in which the changes in Pacific Ocean background state induced by extratropical Rossby waves actually interact with and affect ENSO variability in a more complex setting has not been studied extensively to date. In this study we use a stochastically forced (SF), intermediate-complexity, coupled ENSO model to

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Isaac M. Held, Michael Winton, Ken Takahashi, Thomas Delworth, Fanrong Zeng, and Geoffrey K. Vallis

1. Introduction It is informative to take a simulation of the future climate and, at several times along this trajectory, abruptly return to preindustrial forcing. Matthews and Caldeira (2007) describe calculations of this type using a climate model of intermediate complexity, motivated by geoengineering proposals. Similar calculations with comprehensive climate models have the potential to increase our understanding of the variety of time scales involved in the climate response. In this work

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Leighton A. Regayre, Kirsty J. Pringle, Lindsay A. Lee, Alexandru Rap, Jo Browse, Graham W. Mann, Carly L. Reddington, Ken S. Carslaw, Ben B. B. Booth, and Matthew T. Woodhouse

1. Introduction Aerosols affect Earth’s climate by absorbing and scattering solar and terrestrial radiation ( Twomey 1977 ; Boucher et al. 2013 ). The cloud albedo effect (CAE) ( Boucher et al. 2013 ), characterized by a decrease in cloud drop effective radius that results from an increase in cloud droplet number concentration for a given amount of liquid water ( Twomey 1977 ), is the largest component of the aerosol–cloud interaction. Uncertainty in the magnitude of CAE forcing remains the

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