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Vanda Salgueiro, Maria João Costa, Ana Maria Silva, and Daniele Bortoli

and at the top of the atmosphere (TOA) ( Dong et al. 2006 ). A way of quantifying the cloud radiation effects at the surface and at the TOA is the cloud radiative forcing (CRF), which is defined as an instantaneous change in net total radiation (SW plus LW; in W m −2 ) obtained under cloudy conditions and its clear-sky counterpart; CRF can produce a cooling (negative CRF) or a warming (positive CRF) effect on the earth–atmosphere system. CRF has been a research topic over the last decades because

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Eui-Seok Chung and Brian J. Soden

1. Introduction Climate feedbacks amplify or dampen the initial radiative perturbation induced by a forcing agent through changes in climate variables in response to global-mean surface temperature change. Intermodel differences in climate feedbacks are widely accepted as the primary cause for intermodel spread in the projected future climate changes in response to imposed radiative forcings (e.g., Cess et al. 1990 ; Zhang et al. 1994 ; Colman 2003 ; Bony et al. 2006 ). However, model

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Minghong Zhang and Yi Huang

1. Introduction In the analysis of climate sensitivity, it is a convention to consider radiative forcing to comprise both instantaneous forcing that is due to perturbation in radiative gases (e.g., CO 2 ) and contributions by rapid adjustments of other atmospheric components that are not related to surface temperature change ( Ramaswamy et al. 2001 ). For instance, stratospheric temperature adjustment resulting from the radiative cooling effect of CO 2 is usually considered part of the CO 2

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K. E. Taylor, M. Crucifix, P. Braconnot, C. D. Hewitt, C. Doutriaux, A. J. Broccoli, J. F. B. Mitchell, and M. J. Webb

temperature change. The radiativeforcing” of the system is commonly quantified in terms of the immediate impact of any imposed change on the TOA fluxes. 1 An imposed increase in CO 2 concentration, for example, promptly reduces, by a small amount, the longwave radiation emanating to space and is therefore considered a radiative forcing. The radiative imbalance caused by this forcing tends to warm the system and, in any given model, the global mean temperature response is roughly proportional to the

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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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K. M. Markowicz, P. J. Flatau, J. Remiszewska, M. Witek, E. A. Reid, J. S. Reid, A. Bucholtz, and B. Holben

and middle-troposphere subsidence are responsible for the mostly clear-sky conditions; thus, it was a good site to study the direct aerosol radiative forcing. The purpose of this study is to extend previous knowledge about the aerosol optical properties in the Middle East region. We investigate the influence of aerosol on the surface radiation budget. The results are based on the data collected during 6 weeks of measurements performed at the MAARCO site, including surface and columnar observations

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Bjorn Stevens

consideration of the spatial pattern of the forcing, along with the associated response in regional (and seasonal) surface temperatures, should more strongly constrain , but agree that S15 ’s quantification of this effect is rather speculative. S15 ’s energy budget analysis does not apply equally to all time intervals, as it rests on two ideas: one being that—to separate forcing from feedback—the forced temperature response should share the same sign as its radiative forcing; the other being that the time

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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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U. Schumann, B. Mayer, K. Graf, and H. Mannstein

functions ( Yang et al. 2003 ). With increasing age, the shape and size of contrail particles may approach that of natural cirrus. All these properties make simple radiation estimates difficult. Several studies computed the changes in net downward irradiance (flux) or radiative forcing (RF) caused by additional thin cirrus and contrails ( Stephens and Webster 1981 ; Meerkötter et al. 1999 ; Chen et al. 2000 ; Myhre et al. 2009 ; Rap et al. 2010 ; Frömming et al. 2011 ; Markowicz and Witek 2011

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Norman G. Loeb and Wenying Su

1. Introduction Radiative forcing by aerosols is identified as the largest uncertainty in anthropogenic radiative forcing of climate. Aerosols influence the radiation budget of the earth directly by scattering and absorbing solar radiation (direct radiative forcing) and indirectly by modifying the microphysical characteristics and lifetimes of clouds (indirect forcing). Recently, Forster et al. (2007) provided a review of several model- and observation-based estimates of clear-sky and all

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