Ground-Based Observation of Biologically Active Solar Ultraviolet-B Irradiance at 35.DEG.N Latitude in Japan.

Abstract

A new waterproof broadband UVB radiometer was designed to monitor biologically active solar UVB (290-320 nm) irradiance at ground level. Using this radiometer, solar UVB irradiance has been measured, together with UVA (320-400 nm) and Total (300-3300 nm) solar irradiances, for two years from October 1990 to September 1992. The global UVB solar irradiance shows clear seasonal changes, i.e., approximately by factors of 4 and 2 for the ratios of summer to winter and equinox to winter, respectively. In contrast, the seasonal variations in global UVA and Total are very similar and moderate in amplitude, and the corresponding ratios are about 1.7 and 1.3, respectively. Moreover, it is shown that the seasonal variation in the daily global UVB and that in the killing efficiency of sunlight for bacteriophage T1 have a similar pattern. For UVB and Total irradiances, the diffuse component was separately recorded. The monthly average ratio of the diffuse to the global (direct + diffuse) in UVB is persistently high, being about 80% throughout the year. The monthly average ratio of the diffuse to the global in Total solar irradiance was about 50% for the same period. Based on the present observation we found the 24-month average ratios of monthly global UVB

Variations of erythemal ultraviolet irradiance and dose at Tartu/Tõravere, Estonia

“…The median day appears 5 d after the summer solstice. Similar asymmetry in UV radiation has been observed in Japan at 35°N (Sasaki et al 1993), as well as at erythemal irradiance measurement sites near 45°S in New Zealand (Ryan et al 1996).…”

An Increase in the Global Solar Ultraviolet-B Irradiance at 35.DEG.N in Japan since 1990.

“…However, the global solar UV-B irradiance undergoes a large seasonal variation (see, for instance, Figs. 4 and 5 in Sasaki et al (1993); also, Table 1 of this paper), which tends to mask a relatively small trend. To reduce the seasonal variation we take 12-month moving averages of any quantity x: This procedure is equivalent to applying a numerical low-pass filter; its transfer function is shown in Appendix.…”

“…Monthly averages of daily integrated global solar UV-B irradiances were analyzed for the 43-month (3 years and 7 months) period from October 1990 to April 1994. The data collection is interrupted for two weeks in the middle of November in each year for recalibrations of the instrumental constant and the spectral and angular responses of the radiometer in the manner described by Sasaki et al (1993). Within the accuracies of the measurements no changes have been found in the instrumental constant and in the spectral and angular responses of the radiometer during the period of observation.…”

“…The global solar UV-B irradiance is being measured continuously with high time-resolution by the newly developed band-spectral solar UV-B radiometer at Tokai University in Hiratsuka, Japan, as has been described previously by Sasaki et al (1993). Monthly averages of daily integrated global solar UV-B irradiances were analyzed for the 43-month (3 years and 7 months) period from October 1990 to April 1994.…”

“…A band-spectral solar UV-B radiometer has been developed by us and preliminary results of observations by this instrument have been reported by Sasaki et al (1993). Measurements of global solar UV-B (290-320 nm) irradiance by this radiometer and of global solar Total (300-3300 nm) irradiance by a conventional pyranometer (EKO MS-801) have been conducted at Tokai University at Hiratsuka (35°2' N, 139'2'E) for a 43-month period, October 1990 to April 1994.…”