A method for reconstruction of past UV radiation based on radiative transfer modeling: Applied to four stations in northern Europe

Abstract

[1] A method for reconstruction of past UV radiation has been developed. The idea of the method is to use measurements of global radiation (300-3000 nm) for determining the influence of clouds on UV radiation. In order to transfer the information contained in the global radiation data into a cloud effect in the UV range, a so-called cloud modification table was developed, which is based on physical relationships determined through radiative transfer calculations. The method was given as input the measured global radiation and total ozone column, the total water vapor column from the ERA-40 data set, the surface albedo as estimated from snow depth, and the altitude of the location. Using this method, erythemally weighted UV irradiances were reconstructed back to the early 1980s at four stations in northern Europe: Bergen in Norway, Norrköping in Sweden, and Jokioinen and Sodankylä in Finland. The reconstructed daily UV doses are in good agreement with measurements. For the summer season, the systematic error was found to vary between 0% at Bergen and 4% at Jokioinen, and the correlation coefficient was 0.99 at all stations. The summer root-mean-square error was 5% at all stations except Jokioinen, where it was 9%. The method performs well also for spring and autumn, whereas for winter conditions of low Sun, a systematical underestimation was found. A large part of this underestimation was found to be due to the plane-parallel approximation used in the radiative transfer calculations. The time series of reconstructed UV exhibit a clear increase since the early 1980s at both Sodankylä (4.1%/decade; statistically significant) and Norrköping (3.3%/decade; not significant). At Jokioinen, a weak increase was found, while at Bergen there was no considerable overall change. At both Sodankylä and Norrköping, the increase in the reconstructed UV radiation was primarily driven by an increase in the global radiation, that is, by decreased cloudiness. The method is general in the sense that it can be applied also to other stations.

Reconstruction and analysis of erythemal UV radiation time series from Hradec Králové (Czech Republic) over the past 50 years

“…Correspondingly, the CMF for global radiation (CMF GLB ) was calculated as the ratio between cloudysky (GLB cloud ) and clear-sky global radiation (GLB clear ), as K. Čížková: EUV radiation in Hradec Králové, 1964-2013 shown in Eq. (3) (Lindfors et al, 2007).…”

“…The all-sky EUV radiation was calculated based on global radiation measurements, which is a common method for reconstructing UV radiation doses (e.g., Krzyscin et al, 2004;Lindfors et al, 2007;Rieder et al, 2008). The reconstruction was based on the cloud modification factor (CMF EUV ), which is the ratio between cloudy-sky EUV radiation (EUV cloud ) and clear-sky EUV radiation (EUV clear ), as shown in Eq.…”

“…CMF EUV was obtained using the global radiation observations, since it can be expressed as the function of CMF GLB and solar zenith angle (SZA) (e.g., Lindfors et al, 2007;Bilbao et al, 2011). To obtain the best-fit function and to minimize the RMSE, a multiple nonlinear regression expression, shown in Eq.…”

“…This method can approximate the climatological behavior of aerosols, but it does not consider any yearly variations (Lindfors et al, 2007). The mean daily AOD values for λ = 320 nm (AOD 320 ) were measured by the Brewer spectrophotometer MK-III B184 in the period [2005][2006][2007][2008][2009][2010][2011][2012][2013].…”

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

“…The smoothness of the pattern and the steady increase (before local noon) and decrease (after local noon) of the irradiances provided a criterion for cloudless day. The Tropospheric Ultraviolet-Visible (TUV) RT model by Madronich (1993) is implemented to calculate hypothetical clear-sky daily doses for the selected cloudless days. The TUV input consists of the column ozone amount (taken from the site overpasses by the Solar Backscatter Ultraviolet (SBUV) instrument onboard the NOAA satellites and aerosol characteristics from the AERONET database.…”