UV-B climatology in Central Spain

Broadband ultraviolet-B solar irradiance, 280-315 nm, at ground level in Valladolid (Spain) has been recorded for a 45-month period, from July 2002 to March 2006. Daily maximum of hourly average irradiance values occur in July, 2.02 W m(-2), and minimum, 0.3 W m(-2), in December at solar noon. UV-B daily values follow the pattern of the solar elevation angle; the total accumulated UV-B irradiation along a mean year reaches 7.04 MJ m(-2). A study of the most representative statistical characteristics of hourly average UV-B irradiance and daily irradiation values has been carried out and the results show that the inter-quartile range is small in winter and increases in spring and summer; maximum stability in UV-B takes place at solar noon and around summer; it can be Concluded that this maximum may be considered representative of the UV-B irradiance values. The inter-annual variability has been examined; the monthly-integrated UV-B irradiation values show a large annual cycle with a maximum in July, when the influences of the annual ozone column and summer solstice occur. The UV-B potential and extraterrestrial irradiation has been calculated and determined in order to know the attenuation of UV-B radiation through the atmosphere. It has been obtained that the UV-B percentage transmitted by the atmosphere increases from winter to summer, a maximum value of 10% is obtained in July and a minimum of 4% in December. The atmospheric transparency without clouds oscillates between 10% in spring and 3% in November. Copyright (C) 2008 Royal Meteorological Society