Recent Advances in the Relations between Bright Sunshine Hours and Solar Irradiation

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2008-06-01

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Akınoğlu, Bülent Gültekin

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Chapter 5Recent Advances in the Relations between Bright Sunshine Hours and Solar IrradiationBulent G. Akinoglu1 IntroductionIt seems quite a realistic view to state that the data of bright sunshine hours are the only long term, reliable and readily available measured information that can be used to reach highly accurate estimates of solar irradiation values on the Earth surface.Kimball at 1919 demonstrated for the first time the existence of the relationbetween the average daily irradiation obtained by means of phyroheliometric andphotometric measurements and the duration of sunshine measured by a Marvin sunshinerecorder. He presented the relations graphically and included also the relationbetween the solar irradiation and cloudiness. Using the data of several locations inUSA he came to a conclusion that: “In fact, the radiation-ratio and sunshine dataplot very nearly on the straight line connecting 100% sunshine and 0% sunshineradiation intensities” (Kimball 1919).Alternatively, one might exclaim that the history started at 1924, with a simpleempirical linear relation proposed by Angstr¨om (1924). Since then hundredsof articles appeared in the literature from all over the world which made use ofthis well-known Angstr¨om’s linear correlation in the same, similar and/or modifiedmanner. The correlation derived by Angstr¨om from measured data of Stockholm, inits original form, was:H = Hc (0.25+0.75n/N)(5.1)where H and Hc are the total irradiation income on horizontal surface for a day andfor a perfectly clear sky, respectively while n/N is the time of sunshine expressedas the fraction of greatest possible time of sunshine. One of the chief results thatAngstr¨om reached was “A clear conception of the radiation climate . . . cannot beobtained without a detailed experience of the amount of energy furnished by thediffuse radiation” (Angstr¨om 1924).------------------------Bulent G. AkinogluMiddle East Technical University, Ankara, Turkey, e-mail: bulent@newton.physics.metu.edu.tr

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https://hdl.handle.net/11511/107132

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Department of Physics, Book / Book chapter