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Vijayakumar S. Nair, K. Krishna Moorthy, S. Suresh Babu, and S. K. Satheesh

1. Introduction The optical properties of atmospheric aerosols such as the aerosol optical depth (AOD) and scattering ( σ ) and extinction coefficients, as well as information on their spectral dependencies, are quite important in estimating the radiative impacts and regional climate forcing of aerosols ( Houghton et al. 1995 ; Solomon et al. 2007 ). Aerosols are known to perturb the energy budget of the earth–atmosphere system, both directly by the scattering and absorption of radiation

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B. Kärcher, B. Mayer, K. Gierens, U. Burkhardt, H. Mannstein, and R. Chatterjee

high air traffic density ( Minnis 2003 ). The development of initially line-shaped contrails into cirrus clouds is not well understood; however, contrail cirrus may be the largest component in aviation radiative forcing ( Sausen et al. 2005 ). Given the large uncertainty in evaluating the contrail climate impact despite almost two decades of scientific study ( Forster et al. 2007 ), atmospheric research toward understanding the life cycle, spatial coverage, and microphysical and optical properties

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Bastiaan van Diedenhoven and Brian Cairns

1. Introduction To calculate the effect of ice clouds on Earth’s radiation budget, accurate optical properties are needed that are consistent with the range of ice crystal shapes and sizes present in natural ice clouds ( Stephens et al. 1990 ; Vogelmann and Ackerman 1995 ). Distributions of ice crystal shapes and sizes in clouds depend on many processes, such as depositional vapor growth, sublimation, crystal aggregation, riming, and crystal deposition, which in turn may depend on dynamics

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Laura Mihai and Sabina Stefan

( Vardavas and Taylor 2007 ). It is therefore very important to understand the aerosols effects in the radiative transfer phenomena and to obtain their optical properties with maximum accuracy, both in real time and over the largest possible area of the earth. The optical properties that offer a thorough picture of the aerosol size distribution and mass are the aerosol optical depth (AOD), the Ångström exponent, and the fraction of fine-mode aerosol. In this paper, the results of the statistical analysis

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Xiaodong Liu, Shouguo Ding, Lei Bi, and Ping Yang

1. Introduction Ice clouds remain one of the key uncertainty sources in the study of the atmospheric radiation budget and atmospheric remote sensing ( Liou 1986 ; Lynch et al. 2002 ; Wendisch et al. 2007 ; Minnis et al. 1993a , b ; Baum et al. 2000 , 2005 ; Baran 2009 , and references cited therein). These clouds also pose a challenge to atmospheric radiative transfer and remote sensing studies. As the optical properties of ice crystals are fundamental to quantifying the radiative

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Bastiaan van Diedenhoven, Andrew S. Ackerman, Brian Cairns, and Ann M. Fridlind

asymmetry parameter ( Coakley and Chylek 1975 ; Fu 1996 ; Yang et al. 2000 ; Fu 2007 ). An increasing number of parameterizations for these optical properties of ice clouds are available. Such parameterizations generally relate the optical properties in selected wavelength bands in terms of predicted or imposed bulk characteristics of the ice, such as effective size, shape, and ice water content (e.g., Fu and Liou 1993 ; Fu 1996 ; Wyser and Yang 1998 ; Kristjánsson et al. 1999 ; Yang et al. 2000

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John E. Yorks, Dennis L. Hlavka, William D. Hart, and Matthew J. McGill

their optical and physical properties is necessary. A combination of both in situ and remote sensing measurements is necessary for this climatology, because remote sensing instruments can provide global data in remote regions with high temporal and spatial resolution that are not accessible using in situ measurements ( Wang and Sassen 2001 ). The launches of the Geoscience Laser Altimeter System (GLAS; Spinhirne et al. 2005 ) in January 2003 and the Cloud–Aerosol Lidar and Infrared Pathfinder

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Ping Yang, Zhibo Zhang, George W. Kattawar, Stephen G. Warren, Bryan A. Baum, Hung-Lung Huang, Yong X. Hu, David Winker, and Jean Iaquinta

parameterization of the bulk radiative properties of ice clouds, which is a necessary component of the radiative transfer schemes used in climate models, it is important to learn more about the optical properties of highly complex, nonspherical ice particles. The optical properties are determined fundamentally by the ice habits, particle size distributions, and refractive indices. Furthermore, modeling the optical properties of complex ice particles is also an interesting but challenging research topic in the

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Cenlin He, Yoshi Takano, Kuo-Nan Liou, Ping Yang, Qinbin Li, and Fei Chen

albedo radiative forcing due to BC–snow internal mixing. Nevertheless, observations have shown that nonspherical snow grains are ubiquitous in real snowpack ( Dominé et al. 2003 ; Erbe et al. 2003 ). Many modeling efforts (e.g., Fu et al. 1999 ; Neshyba et al. 2003 ; Grenfell et al. 2005 ) have been made to investigate the shape effect of ice crystals on optical properties by using an effective size (e.g., equal-volume-to-area ratio), which works well for extinction efficiency and single

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Krzysztof M. Markowicz and Marcin L. Witek

forcing for optical depths between 2 and 3 ( Jensen et al. 1994 ; Meerkötter et al. 1999 ) and of nearly 3 ( Fu and Liou 1993 ). These values suggest that some observed contrail-induced cirrus clouds may already exert the strongest possible warming. Here we address some of the existing uncertainties by performing a detailed sensitivity study of contrail radiative-forcing computations on various parameters, primarily on the parameterization of ice-crystal shape and optical properties. Radiative

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