An algorithm for inferring surface UV irradiance including cloud effects

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Date: Oct. 1996
From: Journal of Applied Meteorology(Vol. 35, Issue 10)
Publisher: American Meteorological Society
Document Type: Article
Length: 289 words

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Abstract :

Recent extratropical ozone depletion and the concomitant increase in surface ultraviolet (UV) radiation may be expected to adversely influence the biosphere. Since few long-term, high quality datasets of surface UV are available for assessing these effects, there is a need to develop techniques for estimating past levels of biologically harmful UV at a particular location and thus derive long-term trends. This paper presents a semiempirical algorithm, making use of readily available meteorological variables and total column ozone, for inferring historical UV levels at a particular location, including cloud cover effects. Where input data are available for a network of locations, the technique can be used to generate geographical distributions of surface UV. Measurements made at Lauder (45.04 [degrees] S, 169.68 [degrees] E), from November 1993 to October 1994, were used to establish the relationship between cloud-induced reductions of erythemal UV and broadband irradiance, as a function of solar zenith angle - termed cloud cover modifier functions. To demonstrate the performance of the algorithm, these functions were used to derive 10-min surface erythemal UV irradiances for each day in November 1994. The algorithm makes use of measured broadband irradiances and clear-sky erythemal and broadband irradiances calculated using the following: 1) statistical derivation from measured data and 2) output from a surface spectral irradiance model. Error analysis of the November 1994 surface erythemal UV irradiances indicates an accuracy of 0.12 [+ or -] 0.69 [[micro]watts] [cm.sup.-2]. The percentage error increases with solar zenith angle, with an accuracy of 2 [+ or -] 10% for solar zenith angles less than 55 [degrees]. Although the accuracy deteriorates for larger solar zenith angles, these errors contribute little to the error in calculated erythemal daily doses except in winter where the daily doses are small.

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Gale Document Number: GALE|A18879170