Seasonal variations in total, direct and diffuse UVB in a higher mountainous region in Japan

SUZUKI J., OKANO M. & NATSUAKI T. 2005. Seasonal variations in total, direct and diffuse UVB in a higher mountainous region in Japan. - Phyton (Horn, Austria) 45 (4): (465)-(470). The authors investigated how the intensity of total B Range Ultraviolet Radiation (UVB) and its components such as direct and diffuse UVB varied during 1998 and 1999 in Nagano, a higher mountainous region. The intensity of solar radiation at out of the Earth's atmosphere (Su) and at ground surface (SR) reached a peak at the Summer solstice. However, the peak for UVB did not agree with that of Su, reaching its peak a little bit later than did the peak of Su. Normally, the seasonal variation of total intensity of UVB is affected by solar altitude and ozone concentration in the atmosphere. The ratio of intensity of diffuse UVB to that of direct UVB at noon under fine weather conditions varied by over 0.71 in summer and 2.35 in winter. The slope of the rate decrease of UV-B from autumn to winter was steeper than that of the increase of UVB from spring to summer. The seasonal variation of the component of diffuse UVB was lower than that of the component of direct UVB. However, in autumn and winter when the solar altitude at noon is lower, the component of diffuse UVB was higher than that of the direct one. A daily total UVB of 41.9 kJ/m(2)d was measured on July 30, 1999, the maximum value within the 1998-1999 measuring period. This intensity is approximately 3% higher than the maximum daily total UVB of 40.6 kj/m(2)d, was measured on July 31, 1999, in the lower place, Matsudo, where close to Tokyo, has been reported by KON & al. 2004.