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Carynelisa Erlick, Jonathan P. D. Abbatt, and Yinon Rudich

– 6704 . Anderson , T. L. , D. S. Covert , J. D. Wheeler , J. M. Harris , K. D. Perry , B. E. Trost , D. J. Jaffe , and J. A. Ogren , 1999 : Aerosol backscatter fraction and single scattering albedo: Measured values and uncertainties at a coastal station in the Pacific Northwest . J. Geophys. Res. , 104 ( D21 ), 26 793 – 26 807 . Bates , T. S. , and Coauthors , 2006 : Aerosol direct radiative effects over the northwest Atlantic, northwest Pacific, and north Indian

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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

during the premonsoonal (spring) and monsoonal (summer) periods ( Ackerman and Cox 1989 ). During the summer active dust areas also are located along the Persian Gulf from Kuwait to the UAE. Large anthropogenic emissions ( Langner et al. 1992 ) and the interaction of pollution with mineral dust can lead to complex aerosol particles. Pollution is emitted mostly by local refineries, factories, and fossil fuel combustion, in addition to being transported from the Indian subcontinent. The aerosol optical

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Corinna Hoose, Jón Egill Kristjánsson, Jen-Ping Chen, and Anupam Hazra

contribution of anthropogenic soot to heterogeneous ice nucleation is slightly higher than in the control simulation, the glaciation indirect effect is lower than in previous studies and cannot significantly offset the indirect effects of warm clouds. Numerous uncertainties remain concerning the numerical description of ice nucleation in large-scale models, especially for biological particles: emissions, size distributions, ice nucleation active fractions, hydrophilicity, wet deposition, freezing rates

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Alexander Smirnov, Brent N. Holben, Yoram J. Kaufman, Oleg Dubovik, Thomas F. Eck, Ilya Slutsker, Christophe Pietras, and Rangasayi N. Halthore

1. Introduction Aerosol science returned to prominence in the last decade due to clear evidence of anthropogenic impacts and the important role of aerosols in the radiative forcing of climate. It became evident that in order to understand the effect of greenhouse gases on past climates and on future climate change (e.g., Hansen et al. 2000 ) we need accurate information on aerosol optical properties ( Penner et al. 1994 ) and their direct and indirect (through cloud modification) interaction

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S. K. Satheesh and J. Srinivasan

1. Introduction Radiative forcing due to aerosols is one of the largest sources of uncertainties in estimating anthropogenic climate perturbations ( Charlson et al. 1992 ; Houghton et al. 1995 ). Aerosols are produced by various sources that are highly inhomogeneous in both time and space ( Shaw et al. 1973 ; Prospero et al. 1983 ; Bates et al. 1998 ; Russell et al. 1999 ; Quinn et al. 2000 ). Thus, estimating aerosol radiative forcing is much more complicated than estimating radiative

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L. L. Hood and B. E. Soukharev

) toward the end of the record. At 60°N, however, the last part of the record has no detectable trend and a possible slight upturn appears during the last seven years. As noted, for example, by Fioletov et al. (2002) , the latter upturn appears to occur too rapidly to represent a recovery from chemically induced ozone depletion associated with reduced anthropogenic halogen emissions. Rather, natural climate variability with its effects on stratospheric circulation is a more likely explanation. 3

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R. Li, Q-L. Min, and L. C. Harrison

dust, mostly with the aid of radiation transfer models. To assess dust radiation effects directly from measurements, particularly indirect radiation forcing, we use the CERES Single Scattering Footprint data from both FM3 and FM4 operating modes. Given the extreme concentration of Saharan dust in this case, we ignore the contributions of other aerosols including sea spray, smoke, and anthropogenic aerosols. There are insufficient 100% clear-sky CERES fields of view (FOVs) in the selected area to

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Robert Wood

proposed by Twomey (1977) that increasing the concentration of cloud condensation nuclei (CCN) by anthropogenic means may increase the albedo of clouds. However, there is poor consensus as to the magnitude of the increase ( Lohmann and Feichter 2005 ). Forward models (physical climate prediction models) generally show a much stronger total anthropogenic aerosol signature than is implied by inverse calculations ( Anderson et al. 2003 ). The reasons for the discrepancy are unclear, but may be rooted in

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George Gutman

temperature contrasts, but with nohydrology, Charney showed that an increase in albedo(caused by overgrazing, for example) can producesinking motion which would suppress cloud formationand rain. Independently, Otterman (1974) drew attention to the contrasts in reflectivity in the Sinai,the Gaza Strip and the Negev, and suggested that thebaring of high albedo soils by overgrazing can causeground surface temperature changes which may leadto appreciable regional climate effects. The ensuingmajor criticisms

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Rachel L. Storer and Susan C. van den Heever

( Solomon et al. 2007 ). Particularly, the goal is to understand changes that can occur, to precipitation amount and storm strength, in tropical deep convective clouds because of an increase in the environmental concentration of aerosols (both natural and anthropogenic) that can act as cloud condensation nuclei (CCN). This study investigates these aerosol indirect effects on tropical deep convection utilizing a series of large-scale, high-resolution simulations using a radiative–convective equilibrium

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