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Min Deng and Gerald G. Mace

cirrus occurrence and evolution remain to be understood to the degree that they can be parameterized in numerical models. The main uncertainties stem from the complexities in relating cirrus properties to atmospheric motions. Del Genio (2002) cites the following issues: 1) cirrus encompass a wide range of optical thicknesses and altitudes, 2) the underlying dynamical processes that create cirrus are poorly understood and differ in different parts of the earth, 3) prediction of cirrus formation

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Lazaros Oreopoulos, Robert F. Cahalan, Alexander Marshak, and Guoyong Wen

Introduction Cloud optical property retrieval is one of the main goals of the Earth Observing System (EOS) ( Wielicki et al. 1995 ), and improving the algorithms developed to accomplish this goal is an area of active research. Traditionally, to infer cloud optical depth and particle size, plane parallel theory is used. The standard approach is to construct look-up tables for at least two bands, one absorbing and one conservative with respect to water, using a radiative transfer code such as

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Itamar M. Lensky and Daniel Rosenfeld

criteria that indicate that cloud depth and particle size are large enough to be considered as precipitating clouds. If we use the subscript i to denote the channel, the emissivity of clouds ε i can be expressed in terms of optical depth τ i : ε i = a i (1 − e − τ i ), (1) where a i stands for the effect of scattering on the emissivity. The single scattering albedo of cloud droplets at 11 or 12 μ m is nearly zero ( a 11 = 1), but scattering is not negligible at 3.7 μ m ( a 3.7 < 1) and

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Sundar A. Christopher, Xiang Li, Ronald M. Welch, Jeffrey S. Reid, Peter V. Hobbs, Thomas F. Eck, and Brent Holben

zonal comparison between satellite-based and surface-observed surface radiation budget parameters was in good agreement except in tropical regions where biomass burning is prevalent. Most studies to date have inferred the surface effects of aerosols by comparing the observed radiation budget parameters to calculated values on a monthly mean basis ( Konzelmann et al. 1996 ; Li 1998 ). The major reason for this approach is the lack of information on the optical and radiative properties of aerosols

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M. Chiriaco, H. Chepfer, P. Minnis, M. Haeffelin, S. Platnick, D. Baumgardner, P. Dubuisson, M. McGill, V. Noël, J. Pelon, D. Spangenberg, S. Sun-Mack, and G. Wind

quantify their impact on weather and climate. In addition, ice water content and its spatial distribution are critical to the global radiative effect of cirrus clouds. A large uncertainty in evaluating the radiative impact of ice clouds arises from our limited knowledge of the natural variability of their microphysical properties, such as ice crystal size and shape, which determine their optical characteristics. For example, the effective radius of ice crystals composing cirrus clouds is an important

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Donald C. Norquist, Paul R. Desrochers, Patrick J. McNicholl, and John R. Roadcap

depended on the assumed cirrus extinction when the laser is directed nearly horizontally. Liou et al. (2000) demonstrated a laser transmission model applicable to near-infrared wavelengths in hypothetical scenarios involving thin cirrus clouds with specified optical properties. They computed direct and multiple-scattered transmission from source to target through a specified cirrus layer and found that transmission to the target from multiple scattering was negligibly small. Transmitted energy was

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Timothy J. Nevitt and Craig F. Bohren

wavelengths in the transmission, windowcentered around 10 zm. An exact solution to the problem of scattering by an irregular particle, even if itwere available, would yield more detail than necessary. An alternative approach is to formulate the irregularparticle scattering problem in terms of the kinds of averages inherent in the optical properties of an ensembleof particles. Such a statistical method has been applied to an ensemble of small irregular particles by averagingover a range of electromagnetic

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W. B. Rossow, F. Mosher, E. Kinsella, A. Arking, M. Desbois, E. Harrison, P. Minnis, E. Ruprecht, G. Seze, C. Simmer, and E. Smith

the performance of all current algorithms depends on how accuratelythe clear sky radiances are specified; much improvement in results is possible with better methods for obtainingthese clear-sky radiances. A major difference between the algorithms is caused by their sensitivity to changes inthe cloud size distribution and optical properties: all methods, which work well for some cloud types or climateregions, do poorly for other situations. Therefore, the ISCCP algorithm is composed of a series of

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R. T. Pinker and J. A. Ewing

applied to the optical properties of Rayleigh scattering, water vaporabsorption, aerosol absorption and scattering, and cloud absorption and scattering. Ozone absorption wasalso accounted for. The primary driving input of the model is the cloud optical depth, which can be inferredeither from satellite observations (Experiment A) or from surface cloud observations (Experiment B). InExperiment A, the model was run for the months of May-August 1982 to produce estimates of dailycumulative insolation for

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Kenneth Sassen, Zhien Wang, Vitaly I. Khvorostyanov, Graeme L. Stephens, and Angela Bennedetti

Measurement program, and NASA Grant NAS-7-1407 from the CloudSat program. REFERENCES Atlas , D. , S. Y. Matrosov , A. J. Heymsfield , M-D. Chou , and D. B. Wolf . 1995 . Radar and radiation properties of ice clouds. J. Appl. Meteor. 34 : 2329 – 2345 . Austin , R. T. and G. L. Stephens . 2001 . Retrieval of stratus cloud microphysical parameters using millimetric radar and visible optical depth in preparation for CloudSat. Part I: Algorithm formulation. J. Geophys. Res. 106

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