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Toshihiko Takemura, Teruyuki Nakajima, Oleg Dubovik, Brent N. Holben, and Stefan Kinne

their direct and indirect effects on the climate system have recently been recognized as significant ( Jacobson 2000 ; Ackerman et al. 2000 ). These models were mainly compared with measurements of surface concentrations and several vertical profiles of each aerosol species. In recent years, on the other hand, global distributions of the aerosol optical thickness and Ångström exponent, 1 which are directly related to radiative transfer processes, have been retrieved from satellite- and ground

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Akiko Higurashi, Teruyuki Nakajima, Brent N. Holben, Alexander Smirnov, Robert Frouin, and Bernadette Chatenet

evaluation of the aerosol climate forcing, since satellite retrievals can generate spatially and temporally homogeneous global distributions of aerosol parameters. Present satellite retrievals are limited, however, mainly to estimation of the aerosol optical thickness, which corresponds to the column total cross section of aerosol particles, from one or two channels of polar orbiters, for example, the National Oceanic and Atmospheric Administration’s (NOAA) Advanced Very High Resolution Radiometer (AVHRR

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Philip Stier, Johann Feichter, Silvia Kloster, Elisabetta Vignati, and Julian Wilson

state. Therefore, a nonlinear response of the aerosol optical thickness to emission changes is to be expected and is not further investigated. The annual zonal-mean distribution of the aerosol optical depth ( τ ) and the percent changes for the different scenarios are depicted in Fig. 5 . The strongest effect of anthropogenic emissions on τ can be attributed to the sulfuric emission from fossil fuels, industry, and biofuels. In the NAS scenario, zonal-mean optical depths between 20° and 70°N

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Zhengzhao Luo, William B. Rossow, Toshiro Inoue, and Claudia J. Stubenrauch

, ISCCP results suggest that the production of large amounts of stratospheric aerosol by Mt. Pinatubo is associated with a decrease in cirrus cloud amount by 0.02–0.04 and an increase in their average optical thickness ( Rossow and Schiffer 1999 ). How exactly did Mt. Pinatubo volcano affect cirrus properties? We explore this question by comparing the ISCCP products with two other cloud datasets derived from the split-window method and 3I cloud algorithm ( Stubenrauch et al. 1999a ). In the first half

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Yolanda L. Shea, Bruce A. Wielicki, Sunny Sun-Mack, and Patrick Minnis

aerosol indirect effect can be better constrained by reducing uncertainty in cloud amount, cloud optical thickness, and water cloud effective radius trends. Here, we will focus on the connection between the aerosol indirect effect and water cloud effective radius. A decrease in water cloud effective radius may be indicative of an increased number of cloud condensation nuclei, which are typically dominated by aerosol particles ( Twomey 1977 ). To better constrain radiative forcing and cloud feedback

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Qingyuan Han, William B. Rossow, and Andrew A. Lacis

Northern Hemisphere than in theSouthern Hemisphere. The height dependencies of cloud droplet radii in continental and marine clouds arealso consistent with differences in the vertical profiles of aerosol concentration. Significant seasonal and diurnalvariations of effective droplet radii are also observed, particularly at lower latitudes. Variations of the relationshipbetween cloud optical thickness and droplet radii may indicate variations in cloud microphysical regimes.1. Introduction Cloud

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Mao-Sung Yao and Anthony D. Del Genio

convective and large-scale clouds in climate models appear to produce a threefold variation in one measure of global climate sensitivity ( Cess et al. 1990 ). Notable cloud feedbacks involve changes in cloud height, cloud cover, and cloud optical thickness. Cloud height appears to have a positive feedback for models with prescribed optical thickness decreasing with height. High clouds tend to increase while low and middle clouds tend to decrease by a larger amount in the majority of doubled CO 2

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J. A. Pudykiewicz and A. P. Dastoor

influence of the sulfate aerosol on opticalproperties of the atmosphere. The measurements ofthe optical thickness of the aerosol layer following theMt. Pinatubo eruption were reported by Stowe et al.(1992) and Valero and Pilewskie (1992). The equivalent information could also be derived with some additional assumptions from the sulfate aerosol concentration calculated by the dynamic model with thechemistry terms. The formula used for this purpose isgiven simply by the vertical integral of the

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Ming-Dah Chou and Wenzhong Zhao

surface is shown in the upper panel of Fig. 1 for a solar zenith angle of 60°. It is calculated using a radiation model addressed in the next section. It can be seen in the figure that the surface SW flux is reduced by ≈15 W m −2 for the column water vapor increasing from 3.5 g cm −2 to 6.5 g cm −2 . For a smaller solar zenith angle, the variation in the surface flux due to water vapor is between 15 and 30 W m −2 . The aerosol optical thickness in the IOP is estimated to be 0.12 nearly evenly

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Larry L. Stowe, Herbert Jacobowitz, George Ohring, Kenneth R. Knapp, and Nicholas R. Nalli

spanning over 19 years from September 1981 to December 1999 (see appendix B for notes on the extent of this dataset). The principal dataset parameters are the channel reflectances (%) and infrared radiances [mW(m 2 cm −1 sr) −1 , total cloud amount (%), components of the earth's radiation budget (ERB, W m −2 )] at the top of the atmosphere (TOA); outgoing longwave radiation (OLR), and absorbed solar radiation by the earth–atmosphere system (ASR), and aerosol optical thickness (AOT) over the oceans

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