title: Modification of spectral ultraviolet doses by different types of overcast cloudiness and atmospheric aerosol.
abstract: Wavelength-dependent attenuation of ground-level ultraviolet (UV) dose by different cloud and aerosol situations at the Tartu Observatory site (58°15' N, 26°28' E, 70 m a.s.l) is under scrutiny. The spectra at wavelengths ranging below 400 nm have been recorded by the simple Avantes, Inc. array spectrometer AvaSpec-256 in 2004-2009. The spectral information was supported by the conventional broadband solar irradiance and by the necessary meteorological data. The average cloud modification factor (CMF) on overcast days from May to August has been quite low, 0.36 in UVA and 0.35 in UVB. In the UVA range, the reduction of the daily dose with increasing noon solar zenith angle (SZA) from 35-50° to 65-80° in overcast days has been about 20% more than in clear days, while in the UVB range it was 45% larger. No clear difference in the influence of SZA on CMF between low level (St, Ns) and medium level (As, Ac) overcast cloudiness has been found. The aerosol attenuation during large aerosol optical depth (AOD) episode has been comparable with that of medium level clouds with the wavelength dependency in the UVA range different from that of clouds.
authors.affiliation: University of Tartu, Tartu, Estonia. margit.prussel@ut.ee
authors.forename: Margit
authors.initials: M
authors.lastname: Aun
authors.forename: Kalju
authors.initials: K
authors.lastname: Eerme
authors.forename: Ilmar
authors.initials: I
authors.lastname: Ansko
authors.forename: Uno
authors.initials: U
authors.lastname: Veismann
authors.forename: Silver
authors.initials: S
authors.lastname: Lätt
mesh_terms: D000336:Aerosols; D004307:Dose-Response Relationship, Radiation; D004781:Environmental Exposure; D012621:Seasons; D014466:Ultraviolet Rays
chemical_list: D000336:Aerosols