Effects of clouds on the surface erythemal UV-B irradiance at northern midlatitudes: estimation from the observations taken at Belsk, Poland (1999–2001)

Abstract Results of 2-year measurements at Belsk, Poland, have been analyzed to investigate the effects of clouds on ultraviolet (UV) radiation. Data were collected using a Solar Light UV-biometer 501A (erythemally weighed UV irradiances), Kipp&Zonnen CM11 pyranometer (total solar radiation), and SCI-TEC Brewer Spectrophotometer (total ozone, aerosol and thin cloud optical depth). Hourly reports on total cloud cover and cloud type were also used in this study. It is found that overcast conditions prevail over central Poland and the sky is covered mainly by low-level clouds. The averaged cloud properties derived from visual observations correspond with those estimated from satellite measurements. An empirical relationship has been postulated for the cloud reduction factor of the erythemally weighted UV radiation as a function of the cloud reduction factor for total solar radiation. The relation may be used to reconstruct the past UV-time series. It is established that information of cloud amount and type to estimate the UV-B attenuation provides a substantial uncertainty. Stronger attenuation of the UV radiation by real clouds was found than that estimated by a radiative transfer model when examining results of the cloud optical depth at 320 nm and the cloud attenuation of the UV radiation measurements. The reduction of the erythemally weighted UV irradiance by thin clouds seems to be independent of the cloud type. It is reported that 1.4% of UV-B irradiance measurements were cloud enhanced in the snowless period of the year. The maximum UV-B enhancement of ∼20% greater than an equivalent clear-sky value was found. Numerous enhancements occurred when high-, mid-, and low- (broken Cu) clouds appeared simultaneously. Similar range of the observed enhancements and cloud composition as in previous cloud enhancement studies (over low latitudinal regions) suggest that common mechanisms may govern this phenomenon in low- and mid-latitudinal regions.

[1]  J. Krzyścin,et al.  The surface UV-B irradiation in the Arctic: observations at the Polish polar station, Hornsund /(77°N,15°E), 1996-1997 , 2001 .

[2]  Christos Zerefos,et al.  Spectral measurements of solar UVB radiation and its relations to total ozone, SO2, and clouds , 1993 .

[3]  B. Vogel,et al.  Modelling Of Radiation Quantities And PhotolysisFrequencies In The Troposphere , 1970 .

[4]  M. Ilyas.  Effect of cloudiness on solar ultraviolet radiation reaching the surface , 1967 .

[5]  J. Jarosławski,et al.  On an improvement of UV index forecast: UV index diagnosis and forecast for Belsk, Poland, in Spring/Summer 1999 , 2001 .

[6]  Sethu Raman,et al.  Effects of clouds and haze on UV‐B radiation , 1996 .

[7]  Teruyuki Nakajima,et al.  Modelling radiation quantities and photolysis frequencies in the troposphere , 1994 .

[8]  Philipp Weihs,et al.  Accuracy of spectral UV model calculations: 1. Consideration of uncertainties in input parameters , 1997 .

[9]  V. Kirchhoff,et al.  UV-B optical thickness observations of the atmosphere , 2001 .

[10]  Arve Kylling,et al.  From model intercomparison toward benchmark UV spectra for six real atmospheric cases , 2000 .

[11]  Reijo Visuri,et al.  Performance tests of two Robertson-Berger-type UV meters Solar Light Model 500 and 501 , 1993, Other Conferences.

[12]  Philipp Weihs,et al.  Accuracy of spectral UV model calculations: 2. Comparison of UV calculations with measurements , 1997 .

[13]  Cutchis.  A formula for comparing annual damaging ultraviolet (DUV) radiation doses at tropical and mid-latitude sites. Final report , 1980 .

[14]  Arve Kylling,et al.  Enhanced absorption of UV radiation due to multiple scattering in clouds: Experimental evidence and theoretical explanation , 1998 .

[15]  P. Koepke,et al.  Optical Properties of Aerosols and Clouds: The Software Package OPAC , 1998 .

[16]  T. Landelius,et al.  Effect of clouds on UV irradiance: As estimated from cloud amount, cloud type, precipitation, global radiation and sunshine duration , 2000 .

[17]  Teruyuki Nakajima,et al.  Matrix formulations for the transfer of solar radiation in a plane-parallel scattering atmosphere. , 1986 .

[18]  B. Gardiner,et al.  Setting standards for European ultraviolet spectroradiometers , 1995 .

[19]  D. Hunton.  Charge transfer reactions of metastable Ba(I) and Sr(I) in the CRRES G‐11b Chemical Release Experiment , 1995 .

[20]  B. Mayer,et al.  All‐Weather Comparison between Spectral and Broadband (Robertson‐Berger) UV Measurements , 1996 .

[21]  J. Staehelin,et al.  Influence of snow and clouds on erythemal UV radiation: Analysis of Swiss measurements and comparison with models , 2000 .

[22]  S. Madronich,et al.  Effects of snow cover on UV irradiance and surface albedo: A case study , 1998 .

[23]  Weine Josefsson,et al.  Solar ultraviolet radiation in Sweden , 1986 .

[24]  Catherine Gautier,et al.  SBDART: A Research and Teaching Software Tool for Plane-Parallel Radiative Transfer in the Earth's Atmosphere. , 1998 .

[25]  E. Schlamann,et al.  Total solar radiation and the influence of clouds and aerosols on the biologically effective UV , 1995 .

[26]  M. Blumthaler,et al.  Human solar ultraviolet radiant exposure in high mountains , 1988 .

[27]  G Seckmeyer,et al.  Comparison of Models Used for UV Index Calculations , 1998, Photochemistry and photobiology.

[28]  J. Sabburg,et al.  The effect of clouds on enhancing UVB irradiance at the Earth's surface: A one year study , 2000 .

[29]  M. Degünther,et al.  Effect of remote clouds on surface UV irradiance , 2000 .

[30]  A. Green,et al.  Influence of clouds, haze, and smog on the middle ultraviolet reaching the ground. , 1974, Applied optics.

[31]  J. Krzyścin,et al.  Aerosol impact on the surface UV radiation from the ground‐based measurements taken at Belsk, Poland, 1980–1996 , 1998 .