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James A. Coakley Jr. and Christopher D. Walsh

. A. Coakley Jr. , and M. D. King , 1989 : Direct and remote sensing observations of the effects of ships on clouds. Science , 246 , 1146 – 1149 . Rotstayn , L. D. , 1999 : Indirect forcing by anthropogenic aerosols: A global climate model calculation of the effective-radius and cloud-lifetime effects. J. Geophys. Res , 104 , 9369 – 9380 . Saunders , R. W. , and K. T. Kriebel , 1988 : An improved method for detecting clear sky and cloudy radiances from AVHRR data. Int. J

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D. P. Duda, G. L. Stephens, B. Stevens, and W. R. Cotton

) ABSTRACT Recent estimates of the effect of increasing amounts of anthropogenic sulfate aerosol on the radiative forcingof the atmosphere have indicated that its impact may be comparable in magnitude to the effect from increasesin C02. Much of this impact is expected from the effects of the aerosol on cloud microphysics and the subsequentimpact on cloud albedo. However, internal horizontal variations in cloud optical properties are also known toaffect cloud albedo. A solar broadband version of a 2

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Yi Ming, V. Ramaswamy, Leo J. Donner, Vaughan T. J. Phillips, Stephen A. Klein, Paul A. Ginoux, and Larry W. Horowitz

proportional to LWC 2/3 N 1/3 d ( Twomey 1977 ), indicating that the distribution of water mass among droplets has a direct bearing on the radiative properties of clouds. Such a mechanism is the origin of aerosol–cloud interactions and indirect effects of aerosols. Soluble aerosol particles can be activated into droplets as cloud condensation nuclei (CCN) through dissolution, allowing water condensation to occur at a relatively low supersaturation. As a variety of natural and anthropogenic sources

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Andreas Muhlbauer and Ulrike Lohmann

1. Introduction One of the major challenges in today’s efforts in climate prediction within the framework of the Intergovernmental Panel on Climate Change (IPCC) ( Solomon et al. 2007 ) is to estimate the role of aerosol particles, which interact with clouds and radiation in several ways. In contrast to the greenhouse gases, aerosols are more confined to the local scale. Besides radiative effects, aerosols serve as cloud condensation nuclei (CCN) and are considered to alter the cloud droplet

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William R Cotton and Robert Walko

Abstract

We examine the potential role of aerosol pollution on the rainfall and intensity of hurricane Harvey. For this study, we use the global model, OLAM, with aerosol estimates from the global atmospheric chemistry model GEOS-Chem. Two sets of simulations of hurricane Harvey were performed. Simulations in the first set cover the intensification phase of Harvey until initial landfall in Texas and focus on the sensitivity of storm track and intensity, while simulations in the second set examine the sensitivity of storm track and precipitation during the period after initial landfall when record flooding occurred near Houston. During each period, simulations were performed with no anthropogenic sources of aerosol, with both natural and anthropogenic aerosol sources, and with both sources enhanced ten times.

During the rapid intensification phase, the results indicate that aerosol amounts had very little impact on storm motion. Moreover, very little difference was found on the intensity of the simulated storm to aerosol amounts for the no-anthropogenic vs the GEOS-Chem estimated amounts with anthropogenic sources. However, when both natural and anthropogenic aerosol amounts were enhanced ten times, the simulated storm intensity was enhanced appreciably in terms of minimum sea-level pressure.

During the second period of the simulation, through which Harvey remained a tropical storm, the main result was that very little sensitivity was found in precipitation or any other TC characteristic to aerosol concentrations. We cannot definitively state why the individual convective cells did not respond to high aerosol concentrations during this phase of the storm. However, the abundant precipitation in all three simulations scavenged the vast majority of aerosol as it flowed radially inward, and we speculate that this modulated the potential impact of aerosols on the inner TC and eyewall

Overall, the simulated response of hurricane Harvey to aerosols was far less spectacular than what has been simulated in the past. We conclude that this is because hurricane Harvey was a strongly dynamically-driven storm system that as a result was relatively impervious to the effects of aerosols.

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Jiansong Zhou and Ka-Kit Tung

in the industrial era using the Earth system model version of the Hadley Centre Global Environmental Model (HadGEM2-ES) and attributed the North Atlantic variability to the indirect effect of anthropogenic aerosol's time-varying forcing. However, Zhang et al. (2013) pointed out that the indirect aerosol effects in Booth et al. (2012) are probably overestimated, and the time and spatial signatures in the model's upper ocean are contrary to the observed. Using 330 yr of multiproxy data of near

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Thomas P. Charlock and William D. Sellers

climate. J. Atmos. Sci., 37, 1136-1137.Grassl, H., i979: Possible changes of planetary albedo due to aerosol particles. Man's Impact on Climate, W. Bach, W. W. Kellogg and J. Pankrath, Eds., Elsevier, 229-241.Kellogg, W. W., 1979: Trends in anthropogenic aerosols and their effects on climate. Proc. WMO Tech. Conf. Regional and Global Observations of Atmospheric Pollution Relative to Climate. WMO, Geneva.--, 1980: Aerosols and climate. Interactions of Energy and Climate, W. Bach, J

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William E. Cobb

's elevationwould, in the absence of the mountain effects describedabove, approach a constant level equivalent to themaximum values shown in Fig. 1.5. The oceanic distribution of anthropogenic aerosols Depicted on the world map in Fig. 2 are ocean areaswhere measurements of the atmospheric electrical conductivity indicate a secular increase in aerosol pollution.Conductivity values are shown which also indicateareas where the natural aerosol level remains unaffectedby human activity. The size and intensity

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Stanley F. Woronko

atmospherictransparency). 2) An increase in CO2 content in the atmosphereleads to a decrease in mean hemispheric surfacetemperature. 3) The predominant effect of volcanic and anthropogenic particulates is to reduce the solar flux reachingthe surface, leading to cooling. 4) The assumption of constant mean cloud cover isjustifiable in the modeling of long-term hemispherictemperature trends.The basis for these conclusions derives largely from theapparent high degree of success attained in simulatingthe mean

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Trude Storelvmo, Jón Egill Kristjánsson, and Ulrike Lohmann

1. Introduction a. Aerosol effects on warm and cold clouds The importance of understanding aerosol influence on climate, not only directly but also through their interaction with clouds, has been pointed out in several studies in recent years ( Hansen et al. 2002 ; Kerr 2005 ). The uncertainty associated with the impact of anthropogenic aerosols on clouds is a major contributor to the spread in future climate projections, as the estimates of this aerosol indirect effect (AIE) in different

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