<title>Long-term evaluation of UV-B irradiance in middle-latitude Japan in the 1990s</title>

Abstract

Ground-based global solar ultraviolet-B (UVB) irradiance has been measured by a narrowband-spectral UVB radiometer at Tokai University, Hiratsuka (35 degree(s)21' N, 139 degree(s)16' E) Japan for a 10-year period from October 1990 to September 2000. A precise calibration of the UVB radiometer was periodically performed and the yearly decay sensitivity was found to be -3.7% of the initial sensitivity. Using this decay rate, the measured UVB irradiance was corrected, and the long-term trends of the UVB irradiance were estimated. An increase in the UVB irradiance was demonstrated to be 1.57% per year with a seasonal variation correction, and 1.22% per year with global total solar irradiance and the seasonal variation corrections in addition to quasi-biennial oscillation (QBO) correction. A significant, negative correlation was confirmed between the UVB irradiance normalized by the total solar irradiance and the effective ozone amount ((total ozone amount) x sec (theta) , where (theta) is the solar zenith angle) at Tsukuba, the closest ozone amount measuring site. These findings can be supportive evidence for a direct relationship between solar UVB irradiance and stratospheric ozone amount.