Margit Aun defended doctoral thesis titled "Dependence of UV radiation on climate factors.Reconstruction of UV doses in Estonia for past years"

Tiia Lillemaa | 20.02.2017

On 17 February 2016 junior researcher of Tartu Observatory Margit Aun defended her doctoral thesis titled "Dependence of UV radiation on climate factors. Reconstruction of UV doses in Estonia for past years" at the University of Tartu.

2017-02-17 Margit Aun kaitsmine

Supervisors:
dr Kalju Eerme, Tartu Observatory
dr Hanno Ohvril, Institute of Physics, University of Tartu

Oponents: 
dr Kaisa Lakkala, Finnish Meteorology Institut, Finland
dr Enn Kaup, Tallinn University of Technology

Summary: 

Natural ultraviolet (UV) radiation, reaching the ground, is a part of solar radiation and is divided to UVB (280-315 nm) and UVA (315-400 nm) ranges. Due to high energy UV radiation can influence living organisms, materials as well as atmospheric photochemistry. The public is most interested in the influence of UV radiation on humans, including damage of skin, eyes and immune system. At the same time UV radiation participates in vitamin D synthesis. To evaluate the possible risk of damage or benefit it is important to know the spectral composition (shorter wavelengths are generally more dangerous), received energy and how they are influenced by environmental conditions. The main objective of this work was to investigate the variability of UV radiation reaching the ground in Tõravere, Estonia and how it is influenced by clouds, ozone and aerosols. The dataset is based on measurements conducted at Tartu Observatory since 2004 and on data from Tõravere meteorological station. In clear conditions the daily dose of UVA can reach over 1500 kJ/m2 and over 30 kJ/m2 for UVB. In these high radiation conditions UVI can be over 7. The ratio of UVA and UVB can change more than 10 times during a day in summer. It was found that heavy cloudiness decreases irradiance only by 2/3 during the summer. In addition to data analysis models for calculating daily doses were created and reconstruction of UVB and UVA radiation for period 1955-2003 was made. These models are continuously used for filling measurement gaps. Continuous dataset of daily doses from 1955-2015 is now available. The work was supported by the European Regional Development Fund by financing the Estonian environmental project 3.2.0801.11-0041 "Estonian radiation climate".