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Ann. Geophys., 24, 1767-1782, 2006
www.ann-geophys.net/24/1767/2006/
© European Geosciences Union 2006
Proxy-based reconstruction of erythemal UV doses over Estonia for 1955–2004
K. Eerme1, U. Veismann1, and S. Lätt2
1Tartu Observatory, Tõravere, Tartumaa, Estonia
2Tartu University, Tartu, Estonia
Abstract. A proxy-based reconstruction of the erythemally-weighted UV doses for
1955-2004 has been performed for the Tartu-Tõravere Meteorological
Station (58°16' N, 26°28' E, 70 m a.s.l.) site. The
pyrheliometer-measured daily sum of direct irradiance on partly cloudy and
clear days, and the pyranometer-measured daily sum of global irradiance on
overcast days were used as the cloudiness influence related proxies. The
TOMS ozone data have been used for detecting the daily deviations from the
climatic value (averaged annual cycle). In 1998–2004, the
biases between the measured and reconstructed daily doses in 55.5% of the cases
were within ±10% and in 83.5% of the cases within ±20%,
on average. In the summer half-year these amounts were 62% and 88%,
respectively. In most years the results for longer intervals did not differ
significantly, if no correction was made for the daily deviations of total
ozone from its climatic value. The annual and summer half-yearly erythemal
doses (contributing, on average, 89% of the annual value) agreed within
±2%, except for the years after major volcanic eruptions and one
extremely fine weather year (2002). Using the daily relative sunshine
duration as a proxy without detailed correction for atmospheric turbidity
results in biases of 2–4% in the summer half-yearly dose in the years after
major volcanic eruptions and a few other years of high atmospheric
turbidity. The year-to-year variations of the summer half-yearly erythemal
dose in 1955–2004 were found to be within 92–111% relative to their
average value. Exclusion of eight extreme years reduces this range for the
remaining to 95–105.5%. Due to the quasi-periodic alternation of wet and
dry periods, the interval of cloudy summers 1976–1993 regularly manifests
summer half-yearly erythemal dose values lower than the 1955–2004 average.
Since 1996/1997 midwinters have been darker than on average.
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