Mini-ozoneholes over Central Europe and their influence to the biologically effective ultraviolet radiation

During the past decades a decrease in the total ozone content of the atmosphere (TOC) over Central Europe in the order of 0.6% per year could be observed. For the winter season the decrease is obviously higher than for other times of the year. Mini ozone holes (MOH) occur mostly during winter times and they are responsible for up to 30% of the observed trend for these months. Using TOC measurements made from space (Earth Probe TOMS) and from the ground (Hradec Kralove) we have investigated the impact of MOHs to the biologically effective UV radiation. For our study we introduced three different photobiological effects by applying the action spectrum of the erythema (ERY), that of the generalised plant damage (GPD) and that of DNA damage (DNAD). Two extreme MOHs occurred over Central Europe within the last 5 years, whereas TOC minima cloud be found at a level of 200DU. The first was recognised in January 1998, the second in December 1999. During these MOHs a decrease in order of 50% could be observed within a few days. The increase of the biologically effect UV radiation however was much higher. The highest increase was observed for GPD irradiance (E-GPD). During the MOH of 1998 E-GPD increases from 1.5 mWeff/m2 to 19 mWeff/m2, during the MOH of 1999 from 3 Weff/m2 to 30 mWeff/m2. For E-DNAD the ascent is less dramatically. E-DNAD was starting from approximately 0.5 mWeff/m2 and reached a level of 3.5 mWeff/m2 during MOH 1998, respectively from 0.9 mWeff/m2 to 5.4 mWeff/m2 during MOH 1999. Both MOHs caused a rise by a factor of 6 to 7. Although the lowest increase was found for the E-ERY, the corresponding increase was derived being a factor 3 to 4 for both MOHs.