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Guoxing Chen, Wei-Chyung Wang, and Jen-Ping Chen

only directly reduce the shortwave radiation reaching the surface but also indirectly modify the cloud microphysical properties, resulting in an enhancement in cloud albedo that further reduces the surface insolation. The purpose of the present study is to investigate to what extent the anthropogenic aerosols affect the cloud microphysical properties and their subsequent effects on the surface radiation balance over the SEP within the context of the biases mentioned above. One unique aspect of the

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Kevin J. Noone, Doug W. Johnson, Jonathan P. Taylor, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Philip A. Durkee, Kurt Nielsen, Elisabeth Öström, Colin O’Dowd, Michael H. Smith, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Lieve De Bock, René E. Van Grieken, James G. Hudson, Ian Brooks, Richard F. Gasparovic, and Robert A. Pockalny

1. Introduction a. Anthropogenic effects on cloud albedo It has long been recognized that anthropogenically produced particulate matter can have an effect on cloud albedo. Dramatic examples of such effects have been seen in satellite imagery ever since the early TIROS satellites became operational three decades ago ( Conover 1966 ). A hypothesis presented for the cause of the “anomalous cloud lines” observed in the early TIROS imagery was that particles produced by ships under “rather special

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Alan Robock

temperature about its mean, but alsolong-term excursions from the mean.Various external causes of climate change are also tested with the model and the results compared withobservations for the past 100 years. Volcanic dust is shown to have been an important cause of climatechange, while the effects of sunspot-related solar constant variation and anthropogenic forcing are notevident.1.IntroductionInstrumental surface temperature records have beencompiled for large portions of the globe for about thepast

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Kevin J. Noone, Elisabeth Öström, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Doug W. Johnson, Jonathan P. Taylor, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Colin D. O’Dowd, Michael H. Smith, Philip A. Durkee, Kurt Nielsen, James G. Hudson, Robert A. Pockalny, Lieve De Bock, René E. Van Grieken, Richard F. Gasparovic, and Ian Brooks

droplet number. Such condensation requires only that droplets be present in a supersaturated environment. To increase droplet number, on the other hand, requires that additional particles be present upon which new cloud droplets can form or a supersaturation increase in the cloud. a. Anthropogenic effects on cloud albedo The link between pollution and planetary albedo was pointed out by Twomey (1974) . The notion that anthropogenically produced particles can have an influence on cloud albedo has

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Franziska Glassmeier and Ulrike Lohmann

Générale , Vol. II, International Union of Geodesy and Geophysics, 156–178 . Borys , R. D. , D. H. Lowenthal , S. A. Cohen , and W. O. J. Brown , 2003 : Mountaintop and radar measurements of anthropogenic aerosol effects on snow growth and snowfall rate . Geophys. Res. Lett. , 30 , 1538 , doi: 10.1029/2002GL016855 . Boucher , O. , and Coauthors , 2013 : Clouds and aerosols. Climate Change 2013: The Physical Science Basis , T. F. Stocker et al., Eds., Cambridge University Press, 571

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Surabi Menon, Anthony D. Del Genio, Dorothy Koch, and George Tselioudis

). Recent results from the Monterey Area Ship Track (MAST) experiment ( Ferek et al. 2000 ) and Tropical Rainfall Measuring Mission ( Rosenfeld 2000 ) provide anecdotal evidence that anthropogenically forced decreases in r eff can significantly alter the liquid water path (LWP) and suppress rainfall. Observations of aerosol-induced changes in cloud lifetime have not been reported, however. Observational assessment of both indirect effects is problematic because (a) direct measurements of aerosols and

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S. Garimella, D. A. Rothenberg, M. J. Wolf, C. Wang, and D. J. Cziczo

considered (hereafter stoch). For the stoch case, the cf value for any given call to the ice nucleation scheme is randomly drawn from the measured distribution of cf values reported by Garimella et al. (2017) . Total aerosol indirect effects in the global climate model are diagnosed using the radiative flux perturbation (RFP) method ( Haywood et al. 2009 ; Lohmann et al. 2010 ; Gettelman et al. 2012 ). The top-of-atmosphere radiative flux R is computed using two 6-yr simulations, one with present

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T. A. Rissman, A. Nenes, and J. H. Seinfeld

in the number of cloud droplets formed, negative ϕ (ε o ) values are found for high ε o , which is reflective of increasingly polluted conditions. Therefore, an increase in anthropogenic pollution can have two competing effects on cloud formation: (i) an increased number of CCN activated by increased N ap and (ii), a decreased number of CCN activated by a greater presence of soluble organics. Consequently, regimes exist in which an increase in anthropogenic aerosol can actually lead to a

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G. Pitari, E. Mancini, V. Rizi, and D. T. Shindell

regional variations, with peaks located over Northern Hemisphere midlatitude continental sites. This may potentially imply a strong impact of future emission changes of anthropogenic sulfur, both globally and on regional scales, on SSA with effects on radiation and ozone photochemistry. In this paper results of a three-dimensional global chemical-transport model (CTM) are shown to explore the sensitivity of stratospheric sulfate on anthropogenic sulfur emissions, including subsonic aircraft. A climate

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Jørgen B. Jensen and Sunhee Lee

1. Introduction One of the main unknowns in the prediction of the future climate is the effect of anthropogenic aerosols on clouds and rainfall formation. Both anthropogenic and natural aerosols are thought to act as nuclei for cloud droplet formation. Increasing the aerosol concentration through anthropogenic emissions should theoretically increase the concentration of cloud droplets and simultaneously decrease their average size. For ice-free clouds (warm clouds) it has been hypothesized

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