Reflection of Solar Radiation from an Array of Cumuli

Aida, Masaru

doi:10.2151/jmsj1965.55.2_174

Cited by 18 publications

(7 citation statements)

References 3 publications

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“…As Snow (1985) and Minnis (1989) show, clouds in broken cloud fields appear to occupy increasing portions of a scene as it is viewed from increasingly oblique angles. The cloud fraction apparent from the sun's direction (CF app ) has been used in numerous radiative studies (e.g., Aida 1977;Kobayashi 1988;Barker 1994). The TIPA is closely related to this CF app since both calculate the fraction of the incoming solar radiation that is intercepted by clouds, but TIPA extends the concept of the CF app , which distinguishes only between cloud and no cloud, by also accounting for variations in cloud optical thickness.…”

Section: Fig 3 (A)mentioning

confidence: 99%

“…This approach is different from the one used in previous studies, which focused on how heterogeneities influence the radiation field at various fixed locations. For example, Davis (1992), Marshak et al (1995a), Gabriel and Evans (1996), Davis et al (1997), and Chambers et al (1997) examined the radiation at points of various densities within a cloud with volume extinction coefficient variations; and McKee and Cox (1974), Davies (1976Davies ( , 1978, Aida (1977), Welch and Wielicki (1984), and Bréon (1992) studied the radiation that left cuboidal and cylindrical clouds through their tops and, separately, their sides. The difference between the present approach and other ones is analogous to the difference between the Lagrangian and Eulerian approaches used, for example, in fluid dynamics.…”

Section: Calculation Of Heterogeneity Effects a General Approachmentioning

confidence: 99%

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Effects of Cloud Heterogeneities on Shortwave Radiation: Comparison of Cloud-Top Variability and Internal Heterogeneity

1999

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This paper examines the processes through which cloud heterogeneities influence solar reflection. This question is important since present methods give numerical results only for the overall radiative effect of cloud heterogeneities but cannot determine the degree to which various mechanisms are responsible for it. This study establishes a theoretical framework that defines these mechanisms and also provides a procedure to calculate their magnitude. In deriving the framework, the authors introduce a one-dimensional radiative transfer approximation, called the tilted independent pixel approximation (TIPA). TIPA uses the horizontal distribution of slant optical thicknesses along the direct solar beam to describe the radiative influence of cloud heterogeneities when horizontal transport between neighbors is not considered. The effects for horizontal transport are then attributed to two basic mechanisms: trapping and escape of radiation, when it moves to thicker and thinner cloud elements, respectively. Using the proposed framework, the study examines the shortwave radiative effects of cloud-top height and cloud volume extinction coefficient variations. It is shown and explained that identical variations in cloud optical thickness can cause much stronger heterogeneity effects if they are due to variations in geometrical cloud thickness rather than in volume extinction coefficient. The differences in albedo can exceed 0.05, and the relative differences in reflectance toward the zenith can be greater than 25% for overhead sun and 50% for oblique sun. The paper also explains a previously observed phenomenon: it shows that the trapping of upwelling radiation causes the zenith reflectance of heterogeneous clouds to increase with decreasing solar elevation.

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Section: Fig 3 (A)mentioning

confidence: 99%

Section: Calculation Of Heterogeneity Effects a General Approachmentioning

confidence: 99%

Effects of Cloud Heterogeneities on Shortwave Radiation: Comparison of Cloud-Top Variability and Internal Heterogeneity

1999

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“…The effect of three-dimensional (3D) cloud variability on the transport of solar flux in the atmosphere has been an active area of research for the last three decades (e.g., McKee and Cox 1974;Aida 1977;Davies 1978;Harshvardhan and Thomas 1984;Welch and Wielicki 1984;Barker and Davies 1992;Cahalan et al 1994b;Marshak et al 1995b;Barker et al 1998;O'Hirok and Gautier 1998;Zuidema and Evans 1998;Benner and Evans 2001;Scheirer and Macke 2003;Di Giuseppe and Tompkins 2005). The 3D radiative transfer effect on domain-averaged solar fluxes has been divided into two physical processes, as summarized by Várnai and Davies (1999).…”

Section: Introductionmentioning

confidence: 99%

The Effect of Cumulus Cloud Field Anisotropy on Domain-Averaged Solar Fluxes and Atmospheric Heating Rates

Hinkelman

Evans²,

Clothiaux

et al. 2007

Journal of the Atmospheric Sciences

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Cumulus clouds can become tilted or elongated in the presence of wind shear. Nevertheless, most studies of the interaction of cumulus clouds and radiation have assumed these clouds to be isotropic. This paper describes an investigation of the effect of fair-weather cumulus cloud field anisotropy on domain-averaged solar fluxes and atmospheric heating rate profiles. A stochastic field generation algorithm was used to produce 20 three-dimensional liquid water content fields based on the statistical properties of cloud scenes from a large eddy simulation. Progressively greater degrees of x-z plane tilting and horizontal stretching were imposed on each of these scenes, so that an ensemble of scenes was produced for each level of distortion. The resulting scenes were used as input to a three-dimensional Monte Carlo radiative transfer model. Domain-averaged transmission, reflection, and absorption of broadband solar radiation were computed for each scene along with the average heating rate profile. Both tilt and horizontal stretching were found to significantly affect calculated fluxes, with the amount and sign of flux differences depending strongly on sun position relative to cloud distortion geometry. The mechanisms by which anisotropy interacts with solar fluxes were investigated by comparisons to independent pixel approximation and tilted independent pixel approximation computations for the same scenes. Cumulus anisotropy was found to most strongly impact solar radiative transfer by changing the effective cloud fraction (i.e., the cloud fraction with respect to the solar beam direction).

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“…Cloud field radiative fluxes have been modeled by Aida [1977], Claussen [1982], Welch and Wielicki [1984,1989], Zuev et al [1987], Kobayashi [1989], and others. Cloud shape, mutual shadowing, cloud-cloud interactions, spatial inhomogeneities, and surface albedo have been demonstrated to be important variables.…”

Section: Introductionmentioning

confidence: 99%

“…Most three-dimensional radiation models have assumed uniform cloud spacing. However, Aida [1977] and Kite [1987] have demonstrated that radiative fluxes are sensitive to cloud-size and spatial distributions. Clearly, cloud inhomogeneities and cloud spatial patterns are important variables.…”

Section: Introductionmentioning

confidence: 99%

Clustering, randomness and regularity in cloud fields: 1. Theoretical considerations

Weger¹,

Lee²,

Zhu³

et al. 1992

J. Geophys. Res.

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During the last decade, there has been considerable controversy in the literature concerning the nature of cloud distributions. Both theoretical and observational evidence has been presen• to support cloud field clustering in some cases and cloud field regularity in other cases. Therefore considerable uncertainty exists. It is essential to resolve this issue since it impacts both cloud dynamical and global cloud radiative forcing issues. In the present investigation, analysis and simulation studies based upon nearest-neighbor cumulative distribution statistics, when applied to a point process consisting of cloud centers, show that (1) the Poisson representation of random point processes is superior to pseudorandom number generated models; (2) pseudorandom number generated models bias the observed nearest-neighbor statistics towards regularity; and (3) an upper bound on the errors caused by edge effects in finite areas is shown to be negligible in certain ranges of cloud number density. Interpretation of this nearest-neighbor statistic is discussed for many cases of superpositions of clustering randomness, and regularity. This is accomplished by plotting the observed versus random nearest-neighbor cumulative distribution functions. Both the magnitude of the positive or negative deviations from the diagonal are important indicators of clustering and regularity. Alternative point-to-neighbor statistics are found to be useful for identifying the components of combinations of distribution types. Finally, and perhaps most importantly, the nature and magnitude of cloud size effects upon the nearest-neighbor and point-to-neighbor cumulative distribution curves are investigated. It is found that even at only 15% cloud cover, size effects dominate the bias caused by the lack of randomness of pseudorandom number generators or by edge effects. Furthermore, cloud size effects shift the nearest-neighbor cumulative distribution curves to mimic regularity.

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Reflection of Solar Radiation from an Array of Cumuli

Cited by 18 publications

References 3 publications

Effects of Cloud Heterogeneities on Shortwave Radiation: Comparison of Cloud-Top Variability and Internal Heterogeneity

Effects of Cloud Heterogeneities on Shortwave Radiation: Comparison of Cloud-Top Variability and Internal Heterogeneity

The Effect of Cumulus Cloud Field Anisotropy on Domain-Averaged Solar Fluxes and Atmospheric Heating Rates

Clustering, randomness and regularity in cloud fields: 1. Theoretical considerations

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