Erythemal ultraviolet radiation as deduced from data of ground-based and satellite measurements

Abstract

A comparative analysis of midday values of direct erythemal radiation (ER) from ground-based measurements at Irkutsk and of values of total ER from satellite data for the period 1999-2001 is carried out. A correlation analysis is made of the ground-based of total ER from satellite data for the period 1999-2001 is carried out. A correlation analysis is made of the ground-based and satellite data for separate months and years, and for the input data set for the entire three-year period. In the analysis of the day-to-day variations we identified periods with a high degree of correlation (0.86-0.99) between ground-based and satellite data, as well as periods with distrubances in the consistency of the variations. We discuss the possible reasons behind the features identified and the differences observed in the ER variations of ground-based measurements and satellite data. In the ground-based measurements we identified an asymmetry of the seasonal ER behavior with respect to the summer solstice, implying an increase of ER-values in the second half-year when compared with the first half-year for the same angular altitudes of the Sun. This feature is more poorly pronounced in the satellite data and is distinguished when only days with clear weather are taken into account. A pronounced seasonal behavior of the ER variation coefficients with large values in the second half-year is pointed out.