Daily, seasonal, and annual characteristics of UV radiation and its influencing factors in Tõravere, Estonia, 2004–2016

Systematical spectral ultraviolet (UV) radiation measurements have been carried out in Tõravere, Estonia, since 2004. Together with the data from local meteorology and AERONET stations, satellites, and model calculations, a versatile dataset is available. For the current work, characteristics of daily, seasonal, and annual doses of UVB (280–315 nm) and UVA (315–400 nm) from 2004–2016 are presented and related to global solar radiation, column ozone, and aerosol levels. The annual average UVB dose for 2004–2016 is 3080 kJ/m2 (st. dev. 200 kJ/m2) and UVA dose is 193.4 MJ/m2 (st. dev. 9.8 MJ/m2). Most of the annual radiation is received during summer (~ 57% of UVB and ~ 47% of UVA) and spring. The highest annual UVB doses were recorded in 2005 and 2011, and UVA doses in 2011 and 2013. The lowest values for both wavelength ranges were in 2004 and 2008. UV doses that are noticeably lower or higher from the averages are directly related to longer periods of low/high cloudiness, atypical ozone thickness, or elevated aerosol levels. There are no significant trends in UV radiation doses for the period neither for annual nor seasonal level. The same is true for the factors influencing UV: ozone, global solar radiation, and aerosol optical depth.