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1 May 2005 Photosynthetically Active Sunlight at High Southern Latitudes
John E. Frederick, Yixiang Liao
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A network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high-latitude Southern Hemisphere, from 55°S to 90°S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near summer solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most northern locations, Ushuaia, Argentina and Palmer Station on the Antarctic Peninsula. Near summer solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative-transfer calculations combined with the measured 400–600 nm irradiances allow estimating irradiances integrated over the wavelength band 400–700 nm. This produces a climatology of photosynthetically active radiation for each month of the year at each site.

John E. Frederick and Yixiang Liao "Photosynthetically Active Sunlight at High Southern Latitudes," Photochemistry and Photobiology 81(3), 603-608, (1 May 2005).
Received: 10 May 2004; Accepted: 1 January 2005; Published: 1 May 2005

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