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Optical Engineering

Increasing trend of biologically solar ultraviolet-B irradiance in mid-latitude Japan in the 1990s
Author(s): Masako Sasaki; Shu Takeshita; Takehiko Oyanagi; Yukiharu Miyake; Toshibumi Sakata
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Paper Abstract

Ground-based global solar ultraviolet-B (UV-B: 290 to 320 nm) irradiance has been measured by a narrow band UV-B radiometer at Tokai University, Hiratsuka, Japan (35°21'N, 139°16'E) for a 10-year period from October 1990 to September 2000. A precise calibration of the UV-B radiometer was periodically performed, and the yearly decay in sensitivity was found to be –3.7%. Using this decay rate, the measured UV-B irradiance was corrected, and the long-term trends of the UV-B irradiance were estimated. When the seasonal variation was eliminated by taking 12-month moving averages, an increasing trend in the UV-B irradiance was demonstrated to be 1.57% per year. Moreover, to remove quasibiennial oscillation (QBO), 26-month moving averages were applied to the UV-B irradiance normalized by the global total (300 to 3000 nm) solar irradiance. An increasing trend in the normalized UV-B irradiance was found to be 1.22% per year. In winter, the clearly increasing trend of the UV-B irradiance was statistically significant, although the increasing tendency of the UV-B irradiance in other seasons (spring, summer, and fall) is not clear. A significant inverse correlation was confirmed between the UV-B irradiance normalized by the global total solar irradiance and the effective ozone amount defined as total ozone amount ×secθ, where θ is the solar zenith angle. These findings give supporting evidence for a direct relationship between solar UV-B irradiance and the stratospheric ozone amount. In conclusion, the increasing trend of global solar UV-B irradiance, especially in winter, was confirmed in response to stratospheric ozone loss in mid-latitude Japan in the 1990s.

Paper Details

Date Published: 1 December 2002
PDF: 8 pages
Opt. Eng. 41(12) doi: 10.1117/1.1516823
Published in: Optical Engineering Volume 41, Issue 12
Show Author Affiliations
Masako Sasaki, Tokai Univ. (Japan)
Shu Takeshita, National Institute of Polar Research (Japan)
Takehiko Oyanagi, Tokai Univ. (Japan)
Yukiharu Miyake, EKO Instruments Trading Co., Ltd. (Japan)
Toshibumi Sakata, Tokai Univ. (Japan)

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