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Byung-Ju Sohn and Franklin R. Robertson

Despite the general agreement that clouds cool the earth–atmosphere, there are substantial differences in estimated magnitudes of the annual global mean of cloud radiative forcing. Recent estimates of globally averaged net cloud radiative forcing range from −2 to −27 W m−2. The reasons for these differences have not been clarified in spite of the important role of clouds in maintaining global heat balance. Here, three estimation methods [Earth Radiation Budget Experiment (ERBE), Regression I, and Regression II] are compared using the same data source and analysis period.

Intercomparison has been done for the time period of February and March 1985 over which major satellite radiation budget and cloudiness datasets (ERBE radiation budget, Nimbus-7, and ISCCP cloudiness) are contemporaneous. The global averages of five sets of net cloud radiative forcing by three independent methods agree to within 3.5 W m−2; four of five cases agree to within 1 W m−2. This suggests that differences in published global mean values of net cloud radiative forcing are mainly due to different data sources and analysis periods and a best estimated annual mean among all previous estimates appears to be the ERBE measurement, that is, −17.3 W m−2. In contrast to the close agreement in the net cloud radiative forcing estimates, both longwave and shortwave cloud radiative forcing show more dependence on the chosen method and dataset. The bias of regression-retrieved values between Nimbus-7 and ISCCP cloud climatology is largely attributed to the difference in total cloudiness between two climatologies whereas the discrepancies between the ERBE and regression method appear to be, in part, due to the conceptually different definition of clear-sky flux.

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Nilton O. Rennó, Earle Williams, Daniel Rosenfeld, David G. Fischer, Jürgen Fischer, Tibor Kremic, Arun Agrawal, Meinrat O. Andreae, Rosina Bierbaum, Richard Blakeslee, Anko Boerner, Neil Bowles, Hugh Christian, Ann Cox, Jason Dunion, Akos Horvath, Xianglei Huang, Alexander Khain, Stefan Kinne, Maria C. Lemos, Joyce E. Penner, Ulrich Pöschl, Johannes Quaas, Elena Seran, Bjorn Stevens, Thomas Walati, and Thomas Wagner

understanding of weather and climate. The Intergovernmental Panel on Climate Change (IPCC) and the Decadal Survey ( NRC 2007 ) indicate that the uncertainty in how clouds adjust to aerosol perturbations dominates the uncertainty in the overall quantification of the radiative forcing attributable to human activities. The Clouds, Hazards, and Aerosols Survey for Earth Researchers (CHASER) satellite mission concept responds to the IPCC and Decadal Survey concerns by studying the activation of CCN and their

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Daniel Rosenfeld, William L. Woodley, Alexander Khain, William R. Cotton, Gustavo Carrió, Isaac Ginis, and Joseph H. Golden

CCN concentrations are large, but have little effect when CCN concentrations are small ( Feingold et al. 1998 ; Reiche and Lasher-Trapp 2010 ). Therefore, sea-spray-generated aerosols (GCCN) may partially restore the rain in clouds that would be otherwise suppressed by aerosol pollutants ( Rosenfeld et al. 2002 ). Note that sea-spray-generated GCCN concentrations increase sharply with surface wind speed, especially when reaching hurricane force ( Woodcock 1953 ; Clarke et al. 2006 ; Fairall et

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Steven C. Sherwood, Sandrine Bony, Olivier Boucher, Chris Bretherton, Piers M. Forster, Jonathan M. Gregory, and Bjorn Stevens

including feedbacks is stable if the sum of the α i is smaller than the Planck response. 2 The forcing–feedback paradigm has helped establish, for example, the dominant role of water vapor in amplifying global temperature change and the role of clouds in accounting for its uncertainty ( Cess et al. 1990 ). Many potential feedbacks within the Earth system can be conceived, involving system components having a wide range of characteristic response times ( Dickinson and Schaudt 1998 ; Jarvis and Li

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Lynn M. Russell, Armin Sorooshian, John H. Seinfeld, Bruce A. Albrecht, Athanasios Nenes, Lars Ahlm, Yi-Chun Chen, Matthew Coggon, Jill S. Craven, Richard C. Flagan, Amanda A. Frossard, Haflidi Jonsson, Eunsil Jung, Jack J. Lin, Andrew R. Metcalf, Robin Modini, Johannes Mülmenstädt, Greg Roberts, Taylor Shingler, Siwon Song, Zhen Wang, and Anna Wonaschütz

E-PEACE analyzed aircraft and satellite measurements to separate the aerosol cloud effects of three synthetic particle sources from dynamical variability. Gaps in our fundamental understanding of cloud processes are the central underlying cause of uncertainty in aerosol radiative forcing, even in widespread and well-defined systems such as those for marine stratocumulus cloud formation. Atmospheric aerosol levels have increased markedly since the Industrial Revolution. We do not fully

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Armin Sorooshian, Bruce Anderson, Susanne E. Bauer, Rachel A. Braun, Brian Cairns, Ewan Crosbie, Hossein Dadashazar, Glenn Diskin, Richard Ferrare, Richard C. Flagan, Johnathan Hair, Chris Hostetler, Haflidi H. Jonsson, Mary M. Kleb, Hongyu Liu, Alexander B. MacDonald, Allison McComiskey, Richard Moore, David Painemal, Lynn M. Russell, John H. Seinfeld, Michael Shook, William L. Smith Jr, Kenneth Thornhill, George Tselioudis, Hailong Wang, Xubin Zeng, Bo Zhang, Luke Ziemba, and Paquita Zuidema

Insights and limitations during 500+ flight hours with a single aircraft are used to motivate the dual-aircraft approach in ACTIVATE to study aerosol–cloud–meteorology interactions. The latest Intergovernmental Panel on Climate Change ( IPCC 2013 ) report stated that the largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds. Furthermore, the latest Decadal Survey for Earth Science ( National Academies of

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C. N. Long, S. A. McFarlane, A. Del Genio, P. Minnis, T. P. Ackerman, J. Mather, J. Comstock, G. G. Mace, M. Jensen, and C. Jakob

Tropical Warm Pool— International Cloud Experiment (TWP-ICE; May et al. 2008 ) held in the Darwin area showed that the combination of precipitation amounts from scanning precipitation radar, centrally located soundings, and reanalysis products provides an adequate constraint to construct useful model forcing datasets ( Xie et al. 2010 ). Forcing data can be further augmented by enhanced sounding periods. For example, the ARM MJO Investigation Experiment (AMIE; Long et al. 2010 ) conducted on Manus

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William I. Gustafson Jr, Andrew M. Vogelmann, Zhijin Li, Xiaoping Cheng, Kyle K. Dumas, Satoshi Endo, Karen L. Johnson, Bhargavi Krishna, Tami Fairless, and Heng Xiao

across the domain, the entire LES domain sees the front at the same time as the average of the frontal influence over the forcing region for the particular moment. Because every column is statistically identical, the size of the domain is somewhat irrelevant as long as it is large enough to statistically hold a cloud population consistent with the large-scale forcing. Once that is achieved, the primary advantage of a larger domain is the ability to have better statistical sampling. Figure SB1 shows

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Julia Schmale, Andrea Baccarini, Iris Thurnherr, Silvia Henning, Avichay Efraim, Leighton Regayre, Conor Bolas, Markus Hartmann, André Welti, Katrianne Lehtipalo, Franziska Aemisegger, Christian Tatzelt, Sebastian Landwehr, Robin L. Modini, Fiona Tummon, Jill S. Johnson, Neil Harris, Martin Schnaiter, Alessandro Toffoli, Marzieh Derkani, Nicolas Bukowiecki, Frank Stratmann, Josef Dommen, Urs Baltensperger, Heini Wernli, Daniel Rosenfeld, Martin Gysel-Beer, and Ken S. Carslaw

. 2014 ). Currently, the lack of a well-defined baseline for preindustrial aerosol–cloud interactions introduces large uncertainty in estimates of anthropogenic radiative forcing caused by cloud albedo adjustments due to human activity ( Carslaw et al. 2013 ). Hence, studying aerosol and cloud properties and behavior under preindustrial-like aerosol conditions is essential to reduce this uncertainty. Fundamental questions related to the sources and processes of particles that influence cloud albedo

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P. Jeremy Werdell, Michael J. Behrenfeld, Paula S. Bontempi, Emmanuel Boss, Brian Cairns, Gary T. Davis, Bryan A. Franz, Ulrik B. Gliese, Eric T. Gorman, Otto Hasekamp, Kirk D. Knobelspiesse, Antonio Mannino, J. Vanderlei Martins, Charles R. McClain, Gerhard Meister, and Lorraine A. Remer

from the ACE experience through the Science Definition Team (SDT): extend key systematic ocean biological, ecological, and biogeochemical climate data records and cloud and aerosol climate data records; make new global measurements of ocean color to improve our understanding of the carbon cycle and ocean ecosystem responses to a changing climate; collect global observations of aerosol and cloud properties, focusing on reducing the largest uncertainties in climate and radiative forcing models of the

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