The variations of erythemally weighted ultraviolet (UV) irradiance and its relationships with atmospheric characteristics during 3 annual cycles (1998)(1999)(2000) at 1 site (Tõravere, Estonia; 58.3°N, 26.5°E; 70 m above sea level) were studied, with the further aim to estimate the erythemal doses for past years. In clear sky conditions the daily erythemal dose and noon irradiance exhibit total-ozone-related asymmetry in the annual cycle, with 27% lower values at spring equinox than at autumnal equinox. The clear sky ratio of erythemally weighted to broadband (300 to 3000 nm) irradiance increases from (0.5 ± 0.25) × 10 -4 to (2 ± 0.1) × 10 -4 with an increase in solar elevation from 10°t o 55°. In overcast low cloudiness conditions this ratio is higher. A simple empirical method to estimate the summer half-year erythemal dose for past years is proposed, and the doses were calculated for 1967-2000. A sharp drop in summer half-year sunshine duration and erythemal dose was found around 1975, with a following quasi-linear recovery to the values met in [1967][1968][1969][1970][1971][1972][1973][1974][1975]. A comparison with the measured and Total Ozone Mapping Spectrometer (TOMS)-derived data is provided for 1998-2000. In the fine summer of 1999 and the 'normal' one of 2000, the measured, estimated and TOMS-derived half-year doses agreed to within 0.7%. In the extremely cloudy summer of 1998, the difference between the measured and estimated values was 1.7% and between the measured and TOMS-derived values 6%.KEY WORDS: Erythemal ultraviolet radiation · UV dose · UV index · Atmospheric turbidity · Total ozone · Cloud factor · Relative sunshine duration Resale or republication not permitted without written consent of the publisherClim Res 22: 245-253, 2002, Josefsson & Landelius 2000, Sabburg & Wong 2000. The local UV radiation data records often cover time intervals too short to enable the construction of statistically confident climatic mean annual cycles or to find the trends or periodic changes. This difficulty to some extent is expected to be overcome by using statistical relationships between the UV radiation and major governing factors as the proxies.In the present paper we study the climatologically important relationships between the erythemally weighted UV and the potential proxies, with the final aim of estimating the erythemally weighted UV doses for past years. Summer half-year doses are calculated for 1967-2000 using the relationships found. INSTRUMENTS AND DATA SETSThe UV data were collected in 1998-2000 using the Scintec UV SET sensor at the Tartu/Tõravere Baseline Surface Radiation Network (BSRN) station (58.3°N, 26.5°E; 70 m above sea level). Simultaneous data from routine pyranometric and sunshine-duration measurements, using the Campbell-Stokes heliograph, as well as hourly cloud detection data were used.The Scintec UV SET sensor has an erythemally weighted spectral response (CIE 1987, DIN 5050) and is thermostated to avoid temperature dependence. The spectral response was checked at th...

Abstract. The climatological characteristics of total ozone over Estonia based on the Total Ozone Mapping Spectrometer (TOMS) data are discussed. The mean annual cycle during 1979-2000 for the site at 58.3 • N and 26.5 • E is compiled. The available ground-level data interpolated before TOMS, have been used for trend detection. During the last two decades, the quasi-biennial oscillation (QBO) corrected systematic decrease of total ozone from February-April was 3 ± 2.6% per decade. Before 1980, a spring decrease was not detectable. No decreasing trend was found in either the late autumn ozone minimum or in the summer total ozone. The QBO related signal in the spring total ozone has an amplitude of ± 20 DU and phase lag of 20 months. Between 1987Between -1992, the lagged covariance between the Singapore wind and the studied total ozone was weak. The spring (April-May) and summer (June-August) total ozone have the best correlation (coefficient 0.7) in the yearly cycle. The correlation between the May and August total ozone is higher than the one between the other summer months. Seasonal power spectra of the total ozone variance show preferred periods with an over 95% significance level. Since 1986, during the winter/spring, the contribution period of 32 days prevails instead of the earlier dominating 26 days. The spectral densities of the periods from 4 days to 2 weeks exhibit high interannual variability.

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After having introduced the electronic computer at the W. Struve Tartu Astrophysical Observatory, an opportunity to put into practice some measuring and data handhng systems presented itself. The simplest measuring of variable star brightnesses by the on-line computer was chosen for the beginning, and for today the first stage has passed with certain success. In the present paper we give a brief report about the work done.