An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

The influence of cloudiness over experimental UV erythemal radiation (UVER) has been studied. This influence has been analysed considering total cloudiness and low clouds. The measurements of cloudiness correspond to the daily values registered at 13:00 GMT at the Meteorological Centre of Valencia, which is part of the State Agency of Meteorology of Spain (AEMET). The UVER measurements were made using a YES UVB-1 radiometer located on the roof terrace of the Physics Faculty at the Burjassot Campus, Valencia (latitude 39.508° , longitude − 0.418° , 60 m above sea level). First, a statistical analysis of cloudiness at 13:00 GMT in Valencia was carried out, confirming that the situation is mainly clear skies or very few clouds. Next, the influence of cloudiness on experimental UVER values was analysed, for both total cloudiness and low clouds. The experimental UVER values decrease as cloudiness increases for all solar zenith angles (SZA), and this reduction increases with the zenith angle. Next, the cloud modification factor (CMF) has been defined to reduce the influence of the zenith angle and ozone over the UVER. In order to quantify the relationship between CMF and the degree of cloudiness in oktas, linear, quadratic and potential regressions for both total cloudiness and low clouds have been calculated. Transmissivity due to total cloudiness and for overcast skies reaches 40%. On the other hand, the analysis of the influence over the zenith angle shows that CMF reduces as the zenith angle increases in the case of both total cloudiness and low clouds. With regard to the low cloud CMF, the results are comparable to those proposed by the COST-713 Action “UV-B Forecasting” for partially cloudy or cloudy skies (70% and 50%, respectively). Finally, the relationship between the CMF and the clearness index (k_T) has been analysed, as both parameters are simple indicators of cloudiness. It has been proved that such relationship is close to unity for zenith angles in the mid-range, while the CMF is greater than k_T for lower SZA and is less than k_T for high SZA, which indicates a certain dependence of these two parameters on the zenith angle. Copyright © 2009 Royal Meteorological Society

Although ultraviolet B radiation (UVB), the solar radiation band between 280 and 315 nm, is only a small fraction of the extraterrestrial solar radiation, it accounts for 80% of the harmful effects of exposure to the sun. In this work values of erythemal solar irradiance (UVER) measured in Valencia on a horizontal plane in the period between June 2003 and June 2005 are analysed and compared with measures of UV (A + B) and global irradiances on a horizontal plane. UV erythemal (UVER) irradiance has been measured using a YES‐UVB‐1 broadband radiometer; UV (A + B) irradiance has been measured using a TUVR Eppley radiometer with spectral response between 290 and 385 nm and global irradiance on a horizontal plane has been measured with a Kipp and Zonen model CM‐6 broadband radiometer. A study of a statistically representative index of UVER irradiance has been made by comparing with the results corresponding to UV (A + B) irradiance and those of global irradiance on a horizontal plane. A fit has been performed using all the irradiance values to estimate the UVER and UV (A + B) components as functions of the other ranges. We have calculated for each month the irradiation acumulated during an average day, for the UVER, UV (A + B) and global, the highest values was 4.1, 791 and 25 146 kJ/m² respectively. Copyright © 2007 Royal Meteorological Society