Angular distribution of overcast sky short wavelength radiance

Coombes, Charles A.; Harrison, A. W.

doi:10.1016/0038-092x(88)90085-0

Cited by 20 publications

(6 citation statements)

References 8 publications

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“…Incoming photons strike the cloud at such high angles that multiple scattering and, thus, total extinction are more likely, thus reducing the sky radiance. This horizon-darkening effect is also described in Coombes and Harrison (1988) and can be seen in all the results in this study. Since translucent clouds are optically thinner than obscure-overcast clouds, horizon darkening is more pronounced for the latter conditions.…”

Section: A Comparison Of Vsp Radiance Measurements With Multifractalsupporting

confidence: 65%

The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model

Kuchinke

Fienberg

Núñez

2004

Journal of Applied Meteorology

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In recent years, global warming concerns have focused attention on cloud radiative forcing and its accurate encapsulation in radiative transfer measurement and modeling programs. At present, this process is constrained by the dynamic movement and inhomogeneity of cloud structure. This study attempts to quantify the UV sky radiance distribution induced by a partial and overcast stratiform cloud field while addressing some of the inherent spatial and temporal errors resulting from cloud. For this purpose, high-quality azimuthally averaged 2-min measurements of erythemal UV-B sky radiance distribution were undertaken by a variable sky-view platform at Hobart, Australia (42.90ЊS, 147.33ЊE). Measurements were subsequently compared with Monte Carlo radiative transfer simulations using both a multifractal and plane-parallel homogenous (PPH) cloud field. Data were also compared with several empirical parameterizations. Results at solar zenith angles of 30Њ and 50Њ show that for overcast conditions, the multifractal model is superior to the PPH model. For broken cloud conditions, the radiance measurements are biased toward higher instances of direct-beam interruption by cloud. This tends to smooth the near-sun sky radiance field whereas the multifractal model under the same conditions continues to exhibit the circumsolar effect, indicating that its performance may be still valid for radiation modeling. An empirical parameterization of the same multifractal model produced similar sky radiance profiles, warranting its use in radiative transfer models.

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Section: A Comparison Of Vsp Radiance Measurements With Multifractalsupporting

confidence: 65%

The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model

Kuchinke

Fienberg

Núñez

2004

Journal of Applied Meteorology

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“…The model can also be used to estimate the irradiance within and below the vegetation canopies during partly cloudy and overcast days provided the diffuse fraction of the irradiance is known and the appropriate sky radiance distribution is used in . Sky radiance distributions are available for translucent overcast cloud cover in the SW (25), PAR (12), UV‐A (26) and UV‐B (26) wavebands and for opaque overcast sky conditions in the SW (27), and in the PAR (28), UV‐A (28) and UV‐B (28) wavebands.…”

Section: Methodsmentioning

confidence: 99%

Estimation of Pedestrian Level UV Exposure Under Trees¶

Grant¹,

Heisler²,

Gao³

2007

Photochemistry and Photobiology

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INTRODUCTION Solar ultraviolet radiation (UV) at the earth's surface hasTrees influence the amount of solar U V radiation that many implications for human health. Erythema is caused prireaches pedestrians. A three-dimensional model was demarily by the ultraviolet-B (UV-B) portion of the solar spec-"eloped to predict the ultraviolet-B (UV-B) irradiance trum (280-315 nm) and to a lesser extent by ultraviolet-A fields in open-tree canopies where Qhe spacing between (UV-A) (315-400 nm). There appear to be complex relatrees is equal to or greater than the width of individual tionships between skin cancers and sun exposure (1). Nontree crowns. The model predicted the relative irradiance melanoma skin cancers are thought to be correlated with (fraction of above-canopy irradiance) under both sunlit cumulative lifetime UV exposure (2). Though medical opinand shaded conditions under clear skies with a mean bias ions and epidemiological studies vary as to the relationship error of less than 0.01 and a root mean square error of between sun exposure and cutaneous malignant melanoma 0.07. Both model and measurements showed that the 10-(3), the statement that "it is now well established that sun cations people typically perceive as shady, low-irradiance exposure is one of the probable causes" is genemlly acloeations in the environment can actually have significant cepted by the research community (4). ~h e s e health effects UV-B exposure (4040% of that under direct sunlight).may be exacerbated by depletion of the stratospheric ozoneThe relationship of tree cover in residential neighborlayer and the attendant increases in W radiation (5,6). Alhoods to erythema1 UV-B exposure for children and though changes in habits of recreation and dress, and the adults was modeled for the 4 h around noon in June and increased value placed on a "tan" are evidently largely to blame for most of the increases in skin cancer rates (7), these July. Results showed that human exposures (on the horrates are expected to increase by approximately 2% for every izontal) in cities located at 15 and 30" latitudes are nearly persistent 1% loss in the average ozone concentration (5). identical. For latitudes between 15 and 60°, ultravioletThe human health impact of solar UV at the eanh,s surproteenon (UPF) were less than lor less than face depends on the environmental conditions as well as on 50% tree cover. A UPF of 10 was possible at all latitudes human habits. M~~~ people do not play out their lives in for tree cover of 90%.open fields but reside and work in environments in which there is significant obstruction to the sky and the direct sun by buildings and vegetation. Significant improvemena in the smctures on irradiance in 0 p e n -e cmopies means measured below-canopy irradiance; 1, modeled beldw-canopy rel-.tivs imdiance; I, &red bclow-sanopy =lative irradiance; la that the canopy structure influences the W exposure of peoabove-canopy imdiance; M, tree cover fnnion; MBE. mean bias ple. The mean tree cover of medium-size cities. in-Texas, cr...

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“…The orientation of the receiving plane is contained within the computation of ⌿ d . The cloud-free sky radiance distributions were modeled using distribution functions from the literature (33)(34)(35). The cloudfree F diffuse for the UVB and UVA wavebands were estimated using the Schippnick and Green model (36), while those for the PAR and SW wavebands were estimated using the Bird model (37).…”

Section: Methodsmentioning

confidence: 99%

Multi-waveband Solar Irradiance on Tree-shaded Vertical and Horizontal Surfaces: Cloud-free and Partly Cloudy Skies¶

Grant¹,

Heisler²

2007

Photochemistry and Photobiology

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Irradiance measurements of short wave (SW), photosynthetically active (PAR), ultraviolet‐A (UVA) and ultraviolet‐B (UVB) solar radiations were made on horizontal and vertical surfaces in the shade of trees under cloud‐free and partly cloudy skies. All measurements were referenced to the irradiance of a horizontal surface above the canopy. For horizontal shaded surfaces under cloud‐free skies, the values of the ratio (Rh) of below‐ to above‐canopy horizontal irradiance were similar for the UVA and UVB wavebands and for the SW and PAR wavebands. However, Rh for the UV wavebands differed from that for the PAR and SW wavebands. Overall, values of Rh in the shade typically varied as PAR < SW ≪ UVA < UVB. The irradiance ratios for vertical surface in the shade typically varied as UVB > UVA = SW > PAR. In absolute terms, UVB irradiance (Ih) on tree‐shaded horizontal surfaces increased relative to a cloud‐free sky when a translucent cirroform cloud was in front of the sun, but decreased when the cloud was in a region of sky away from the sun. Translucent cirroform cloud cover also tended to decrease the UVB irradiance (Iv) for a shaded vertical surface (either facing the sun or south) relative to that under cloud‐free skies, regardless of where the clouds were in the sky. In all other wavebands the shaded Ih and Iv increased under translucent cirroform cloud cover relative to cloud‐free skies, regardless of where the clouds were in the sky.

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Angular distribution of overcast sky short wavelength radiance

Cited by 20 publications

References 8 publications

The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model

The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model

Estimation of Pedestrian Level UV Exposure Under Trees¶

Multi-waveband Solar Irradiance on Tree-shaded Vertical and Horizontal Surfaces: Cloud-free and Partly Cloudy Skies¶

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