Spectral UV measurements in Austria from 1994 to 2006: investigations of short- and long-term changes

S Simic,A Vacek,H Kromp-Kolb,M Fitzka,P Weihs

doi:10.5194/acp-8-7033-2008

Abstract

Abstract. The influence of variability of atmospheric parameters on short- and long-term changes of spectral UV irradiance measured at the Sonnblick observatory (47.03° N, 12.57° E, 3106 m) during the period from 1994 to 2006 is studied. Measurements were performed with the Brewer #093 single-monochromator spectrophotometer and with a Bentham DM 150 spectroradiometer (double-monochromator). The influence of ozone, albedo, snowline and clouds on UV variability is evaluated for each parameter separately using 10-year climatology. It is found that the effect of total ozone on short-term variability of UV irradiance at 305 nm can be more than 200% and on average more than 50%. Clouds can cause variability of 150% or more and on average 35%. Variability caused by albedo reaches a maximum of 32% in April (6% on average). In summer and autumn, total ozone and clouds strongly influence the variability of UV radiation, whereas in winter and spring ozone has the more pronounced effect. A decrease in snowline height from 3000 m to 800 m a.s.l. enhances the UV irradiance by a factor of 1.24 for clear sky conditions and by a factor of 1.7 for 8/8 cloud cover. Long-term trends are investigated for the time period from 1994 to 2006 based on clear-sky measurements, using the non-parametric Mann-Kendall trend test. Significant downward trends (99% confidence level) are found for solar zenith angle 55° at wavelengths from 305 nm to 324 nm and erythemally weighted irradiance according to CIE, which are caused by an increase in sunshine duration during periods of high total column ozone. Significant trends (90% confidence level) were also found for other combinations of wavelength and SZA.

Highlights

UV irradiance reaching the earth’s surface is influenced by the concentration of stratospheric ozone as well as by further atmospheric parameters, such as clouds, aerosols, and surface albedo
Knowledge of spectral UV irradiance and its dependence on these parameters, which may change in the future, are prerequisites to quantitatively understand and estimate future UV radiation
The first spectrally resolved routine measurements started in the 1990s, studies on long-term changes in spectral UV irradiance are hampered by the limited number of years of available data (Zerefos et al, 1997; Lakkala et al, 2003; Glandorf et al, 2005)

Summary

Introduction

UV irradiance reaching the earth’s surface is influenced by the concentration of stratospheric ozone as well as by further atmospheric parameters, such as clouds, aerosols, and surface albedo. Increase of UV radiation during the last decades is reported where a decrease of stratospheric ozone has been observed (Kerr and McElroy, 1993; Zerefos et al, 1997, 2001; Bartlett and Web, 2000). The magnitude of this change and their causes are, uncertain, calling for more detailed investigations of the influence of clouds, albedo, and other atmospheric parameters on UV radiation (Kerr and Seckmeyer et al, 2003; Bais and Lubin et al, 2007). The first spectrally resolved routine measurements started in the 1990s, studies on long-term changes in spectral UV irradiance are hampered by the limited number of years of available data (Zerefos et al, 1997; Lakkala et al, 2003; Glandorf et al, 2005)

Methods

Results

Conclusion