Articles | Volume 18, issue 1
Research article
02 Jan 2018
Research article |  | 02 Jan 2018

Trends in erythemal doses at the Polish Polar Station, Hornsund, Svalbard based on the homogenized measurements (1996–2016) and reconstructed data (1983–1995)

Janusz W. Krzyścin and Piotr S. Sobolewski

Abstract. Erythemal daily doses measured at the Polish Polar Station, Hornsund (77°00′ N, 15°33′ E), for the periods 1996–2001 and 2005–2016 are homogenized using yearly calibration constants derived from the comparison of observed doses for cloudless conditions with the corresponding doses calculated by radiative transfer (RT) simulations. Modeled all-sky doses are calculated by the multiplication of cloudless RT doses by the empirical cloud modification factor dependent on the daily sunshine duration. An all-sky model is built using daily erythemal doses measured in the period 2005–2006–2007. The model is verified by comparisons with the 1996–1997–1998 and 2009–2010–2011 measured data. The daily doses since 1983 (beginning of the proxy data) are reconstructed using the all-sky model with the historical data of the column ozone from satellite measurements (SBUV merged ozone data set), the snow depth (for ground albedo estimation), and the observed daily sunshine duration at the site. Trend analyses of the monthly and yearly time series comprised of the reconstructed and observed doses do not reveal a statistically significant trend in the period 1983–2016. The trends based on the observed data only (1996–2001 and 2005–2016) show declining tendency (about −1 % per year) in the monthly mean of daily erythemal doses in May and June, and in the yearly sum of daily erythemal doses. An analysis of sources of the yearly dose variability since 1983 shows that cloud cover changes are a basic driver of the long-term UV changes at the site.

Short summary
Maintaining homogeneity of long-term UV time series taken from various instruments and thus trend estimation are challenging tasks, especially for remote Arctic sites. Highlights: method of the UV data homogenization is proposed to be used at any remote site. Past UV data built from satellite total O3 and ground-based sunshine duration. Yearly UV doses trendless in the southern Svalbard for 34-year period since 1983. Long-term cloud effects on UV more important than the ozone effects there.
Final-revised paper