Dependence of the Index of Biologically Active Ultraviolet Radiation on the Season and Time of Day

Abstract

In the present work, the data from the monitoring of the biologically active ultraviolet (UV) radiation of the Sun at the National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences for the period 2007–2021 were used. Based on the data analysis, a statistical method is proposed for determining the UV radiation index values in clear weather. As a result, estimated values of the UV-Index for each day of the year and for each hour are obtained, which can be used for predicting when reporting the cloud forecast. In the present paper, the applicability of the theoretical dependence of the UV-Index on the square of the cosine of the zenith angle of the Sun is investigated. The seasonal dependence of UV-Index values at fixed zenith angles of the Sun is discussed. Through regression analysis, the influence of the Total Ozone Column (TOC) and the concentration of particulate matter with d < 10 μm (PM10) on the UV-Index in the conditions of the city of Sofia was investigated. Explanations of the obtained results are offered.