Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

“P h ysics o f Auroral P henom ena", Proc. XXXIII A n n u a l Sem inar, A patity, pp. 1 78 - 181, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute 10 YEARS INVESTIGATIONS OF THE SOLAR UV RADIATION AND TOTAL OZONE IN STARA ZAGORA, BULGARIA B.D. M endeva Ts.N. G o g o sh ev a2, D.G. K rastev 1 1. Solar Terrestrial Influences Laboratory, Bulgarian Academy o f Sciences, Stara Zagora Department, Bulgaria 2. Institute o fAstronomy, Bulgarian Academy o f Sciences, Sofia, Bulgaria Abstract. Some major results from the ground-based measurements of the ultraviolet solar radiation and total ozone content (TOC), performed in Stara Zagora (42°25‘N, 25°37’E), Bulgaria in the last decade, are presented. The UV radiation reaching the Earth’s surface at different conditions is investigated. The ozone amount is determined using the scanning ultraviolet spectrophotometer Photon, which measures the direct solar UV radiation (300-360 nm). The TOC dynamics is analyzed using data from ground-based measurements made by Photon, as well as these by satellite instruments (GOME, TOMS-ЕР and SCIAMACHY). The seasonal TOC variations are clearly marked. Quasi-biennial periodicity in the amplitude of the ozone maximums can be seen. The experimental data show that there is no any trend in the ozone course during the period 1997-2008. The solar eclipse is an event, which gives the opportunity to receive important information about the sun itself as well as about the influence o f the solar radiation on the processes, defining the atmospheric components dynamics. The results from the TOC and UV measurements during two solar eclipses: on 29 March 2006 and on 11 August 1999, carried out in Stara Zagora, are presented. Introduction The ultraviolet radiation has the strongest biological effect of the whole solar radiation spectrum. Depending on the irradiance intensity, the wavelength and the conditions o f the Earth’s atmosphere, the UV radiation has both positive and negative effect on the biosphere. The significance of the relation between the total ozone content (TOC) in the atmosphere and the quantity of ultraviolet radiation (UVR) reaching the Earth’s surface, stimulates the research in this area, especially after the certain reduction of the ozone layer, established in the last decades and the related increase of the UVR, dangerous for the biosphere. The impact of the ozone content on the UVR, penetrating the atmosphere and reaching the Earth’s surface is both qualitatively analyzed and quantitatively evaluated in a number of publications [1 ,2 ,3 ]. The role of the ozone for the thermal balance and the temperature structure o f the Earth’s atmosphere is examined as well as its importance as a trace species and a major participant in the photochemical processes [4, 5]. That is why in the last years the dynamics of the atmospheric ozone is actively monitored both through measurements by ground- based instruments, located in a large number of stations all over the globe and by instruments on board artificial satellites. The aim of this paper is to present some results of the UV and ozone investigations using ground-based measurements, performed in Stara Zagora, Bulgaria, and satellite data in the last decade. Instrum en ts and methods The ground-based measurements are performed in Stara Zagora, by the scanning spectrophotometer Photon [6]. This instrument is used to measure and examine the temporal variations of the ultraviolet radiation, reaching the Earth’s surface and the total ozone content (TOC) in the atmosphere. The spectrophotometer measures the direct solar light in the range 300-360 nm, with 1 nm resolution. The sensor is a Seya-Namioka monochromator with a concave diffraction grating, connected with a stepper motor, performing the scanning. A photoelectronic multiplier is used as a photoreceiver, sensitive in the UV part of the spectrum. The sensor o f the spectrophotometer is fixed on the solar-tracking system of a telescope. This ensures high precision of the instrument orientation to the Sun and permanent illumination o f the input slit during spectrum scanning. The scanning time interval of the specified range is 140 s. The system is controlled by a microprocessor and a PC records the data. The calibration is made by a mercury lamp and by intercalibration with a sample Brewer spectrophotometer in Greece and Norway. The method for determination of the total ozone content is similar to the method, applied in the classical Brewer spectrophotometers. TOC is determined from direct solar spectra by applying the Bouguer-Lambert’s law for radiation attenuation during transition through the Earth’s atmosphere and different absorption o f the separate wavelengths by the ozone molecules. We, however, use the intensity of rather more wavelength pairs (about 20). In this way enhanced precision in the determination o f TOC 178