A comparative analysis of midday values of direct erythemal radiation (ER) from ground-based measurements at Irkutsk and values 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 some months and years, and for the input data for the entire three-year period. In the analysis of the day-to-day variations, we identified periods with a high degree of correlation (0.84-0.99) between ground-based and satellite data, as well as periods with disturbances in the consistency of the variations. We discuss possible reasons of 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, consisting in increase of ER-values in the second half-year as compared with the first half-year for the same angular elevations 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 behaviour of the ER variation coefficients with minimum in June is pointed out.