UV Index experimental values on vertical surfaces.

UV erythemal irradiance (UVER) has been studied on a horizontal plane and on vertical surfaces with different orientations in Valencia, Spain. The evolution of the solar noon value and the maximum daily value over a year has been analysed from the instantaneous UVER taken every five minutes on the horizontal plane and on vertical surfaces with north, south, east and west orientations. The annual evolution of these values shows a sinusoidal form for all planes except for the vertical south plane with maxima in spring and autumn. The UV Index (UVI) on these planes was also determined. The percentage of coincidence of the UVI at solar noon and of the maximum daily UVER values, considering differences of 1 or 0 units, is 87% on the horizontal plane, 100% on the vertical north plane, 92% on the vertical south plane, 77% on the vertical east plane and 75% on the vertical west plane. We have compared the UVI of the vertical plane with the horizontal one by means of linear regressions. All planes show very good correlations except for the vertical south plane, which shows no correlation with the horizontal plane for the middle days of the year due to its particular geometry with respect to the Sun's apparent path. Finally, the annual cumulative UVER doses related to each phototype for the horizontal and vertical planes were calculated. It was noticed that the dose over a year on the horizontal plane doubles the dose on the vertical south plane, which is the one that receives the maximum dose. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]