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Lothar Schüller, Ralf Bennartz, Jürgen Fischer, and Jean-Louis Brenguier

Introduction Monitoring changes of cloud microphysical and radiative properties due to anthropogenic pollution is crucial for validating climate model predictions of the indirect aerosol effect (e.g., Twomey 1977 ). Retrieval techniques of cloud optical properties from satellite-measured radiances have been under developed since the late 1980s (Twomey and Cocks 1989; Nakajima and King 1990 ) and are used to operationally retrieve optical thickness and effective droplet radius from orbiting

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Ming-Dah Chou, Guoliang Ji, Kuo-Nan Liou, and Szu-Cheng S. Ou

secondary as compared to the uncertainties induced by the cloudamount, cloud optical thickness, and aerosols. With the use of (1) and (3), the computed cloudamount, optical thickness, and temperature (or height)are consistent with the satellite-measured radiancesaveraged over a 0.25- x 0.25- latitude-longitude region. It is apparent that the estimated cloud parametersare dependent upon the subjectively specified cloudthreshold ath. Nevertheless, it has been shown in Chou( 1991 ) that if Otth is

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Ana B. Ruescas, Manuel Arbelo, Jose A. Sobrino, and Cristian Mattar

measurements: Global validation and intersensor comparisons . IEEE Trans. Geosci. Remote Sens. , 44 , 2184 – 2197 . Guerzoni, S. , and Chester R. , 1996 : The Impact of Desert Dust Across the Mediterranean . Kluwer Academic Publishers, 387 pp . Husar, R. , Prospero J. , and Stowe L. , 1997 : Characterization of tropospheric aerosols over the oceans with the NOAA Advanced Very High Resolution Radiometer optical thickness operational product . J. Geophys. Res. , 102 , 16 889 – 16 909

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Y. J. Kaufman, T. W. Brakke, and E. Eloranta

theearth-atmosphere system. A field experiment was conducted to test this theory. In the experiment the upwardradiance was measured above and below a haze layer during simultaneous measurements of the haze characteristics. The measurements were conducted at a narrow near-IR channel (773 k 22 nm) which represents thevisible and near-IR spectral region. The aerosol vertical optical thickness at eight wavelengths, as well as thevertical and horizontal profiles of the scattering coefficient, the

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Kenneth Sassen and John D. Horel

. . -quantities representing the average of all lidar profilescollected during the four observation periods are givenin Fig. 7a-d. Table 1 summarizes these findings. The scattering ratio profiles in Fig. 7 clearly showthe gradual ascent, at a rate of '~0.6 km day-l, andstrengthening of the cloud layer peak. By 7 August,only a residual aerosol layer between ~ 14.0-16.0 kmwas observed in the lower stratosphere. Optical thickness estimates, based on the use of an average backscatter-to-extinction ratio of k

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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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Bryan A. Baum, Ping Yang, Andrew J. Heymsfield, Carl G. Schmitt, Yu Xie, Aaron Bansemer, Yong-Xiang Hu, and Zhibo Zhang

clouds from different flight tracks from synoptic cirrus and tropical convection. For the lidar, the signal becomes attenuated for clouds that are optically thick ( τ ≥ 3, where τ is optical thickness). This figure shows the cloud boundaries observed by the aircraft (solid circles) and the penetration distance from cloud top that is observed by a lidar. When τ = 3 in this figure, an arrow is placed on the vertical bar. For synoptic ice clouds the lidar generally penetrated very deeply into the

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Kuo-Nan Liou

. Since a number of uncertainties suchas the number density, the absorption coefficients, andthe vertical inhomogeneity associated with the opticalproperties of aerosols, are involved, use was made ofthe dimensionless vertical scale with optical thicknesses 0 0.2 0.4.-h,' 0 ItU..o: 0,2 X: L5H. ~-N: 0.50.02 0.04 0.06 1,-cH?/I \x:,o,t, 1-0.004 -0.002HEATING RATE (C/houri/c) COOLING RATE FIG. 20. The

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G. Pitari and V. Rizi

tropical latitudes where the optical thickness ofvolcanic particles has remained sufficiently high for several months after the eruption. The radiative interactionwith stratospheric trace species not only takes place through changes in photodissociation frequency but is alsoa consequence of solar and planetary radiation absorption by the aerosol particles. The resulting heating ratesproduce a nonnegligible equatorial upwelling whose effects on dynamics and transport have been studied usinga three

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W. E. Meador and W. R. Weaver

equations if the intensity is replaced by integrals ofthe intensity over hemispheres. One set of solutions thus suffices for all methods and provides convenientanalytical comparisons. The equations also suggest modifications of the standard techniques so as toduplicate exact solutions for thin atmospheres and thus permit accurate determinations of the effects oftypical aerosol layers. Numerical results for the plane albedos of plane-parallel atmospheres (singlescattering albedo = 0.8, 1.0; optical

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