Reconstruction of UVB and UVA radiation at Tõravere, Estonia, for the years 1955–2003

Abstract

Information on UV radiation levels and their changes in the past improves opportunities to investigate negative and beneficial effects of radiation. A reconstruction of the daily doses of ground-level solar irradiance in ultraviolet wavelength bands UVB (280-315 nm) and UVA (315-400 nm) in the years 1955-2003 was made for the site of Tartu Observatory at Toravere, Estonia (58°16N, 26°28E, 70 m a.s.l.). Freely available software ARESLab (based on Multivariate Adaptive Regression Splines, MARS) was used for radiation modelling. Measured daily column ozone values, daily dose of global solar radiation, noon solar zenith angle, and cloudless UV daily doses calculated with the libRadtran software packet were used as the input data. The construction of the models was based on the UV spectral irradiance data measured at Toravere from 2004 to 2006 with a minispectrometer AvaSpec-256. The models were tested on a 200-day data set from the year 2007. The coefficients of linear correlation between the calculated and measured daily doses were 0.98 in both wavelength ranges. Testing was also carried out on the data from Bentham DMc150F-U to investigate the possibility of providing information for missing measurement days with model calculations in order to obtain longer time series and better opportunities for investigating short-term changes and short- period dependence between UV doses and various weather and atmospheric factors and ground ecosystems.