ABSTRACT Stratospheric ozone depletion, as a result of increasing chlorofluorocarbons in the stratosphere, allows more UV-B irradiance (290 - 325 nm) to reach the earth’s surface with possible detrimental biological effects. Be-cause there are few UV-B radiation stations, irradiance models are useful tools for estimating irradiances where measurements are not made. Estimates of spectral and broadband irradiances from a numerical model are compared with Brewer spectrophotometer measurements at nine Canadian stations (Alert, Resolute Bay, Churchill, Edmonton, Regina, Winnipeg, Montreal, Halifax and Toronto) and 26 years of data. The model uses either the discrete ordinate radiative transfer (DISORT) or the delta-Eddington algorithms to solve the radiative transfer equation for a 49-layer, vertically inhomogeneous, plane-parallel atmosphere, with cloud inserted between the 2 and 3 km heights. Spectral calculations are made at 1 nm intervals. The model uses extraterrestrial spectral irradiance, spectral optical properties for each atmospheric layer for ozone, air mole-cules, and aerosol and surface albedo. A fixed broadband cloud optical depth of 27 was satisfactory for cal-culating cloudy sky irradiances at all stations except in the arctic.
Comparisons are made both for daily totals and for monthly averaged spectral and broadband irradiances. The delta-Eddington method is shown to be unsuitable for calculating spectral irradiances under clear skies, at wavelengths less than 305 nm where absorption by ozone is high, and at large solar zenith angles. The er-rors are smaller for overcast conditions. The method is adequate for daily total and monthly averaged spec-tral (? 305 nm) and broadband calculations for all sky conditions, although consistently overestimating ir-radiances. There is a good agreement between broadband measurements and calculations for both daily totals and monthly averages with mean bias error mainly less than 5% of the mean measured daily irradiance and root mean square error less than 25%, decreasing to below 15% for monthly averages.
Cite this paper
nullJ. Binyamin, J. Davies and B. McArthur, "Validation of Spectral and Broadband UV-B (290 - 325 nm) Irradiance for Canada," Atmospheric and Climate Sciences, Vol. 1 No. 3, 2011, pp. 69-85. doi: 10.4236/acs.2011.13008.
 J. E. Frederick, H. E. Snell and E. K. Haywood, “Solar ultraviolet radiation at the earth's surface,” Phtochem. Phtobiol., Vol. 50, 1989, pp. 443-450.
 L. T. Molina and M. J. Molina, “Absolute absorption cross sections of ozone in the 185-350 nm wavelength range,” J. Geophys. Res., Vol. 91, 1986, pp. 14501- 14508.
 D. Lubin, B. G. Mitchell, J. E. Frederick, A. D. Albert's, C. R. Booth, T. Lucas and D. Neuschuler, “A contribution toward understanding the biospherical significance of Antarctic ozone depletion,” J. Geophys. Res. Vol. 97, 1992, pp. 7817-7827.
 S-C. Tsay and K. Stamnes, “Ultraviolet radiation in the Arctic: The impact of potential ozone depletions and cloud effects,” J. Geophys. Res., Vol. 97, 1992, pp. 7829- 7840.
 P. Wang and J. Lenoble, “Comparison between measurements and modeling of UV-B irradiance for clear sky: a case study,” Appl. Opt., Vol. 33, 1994, pp. 3964-3971.
 P. M. de F. Forster, K.P. Shine and A.R. Webb, “Modelling ultraviolet radiation at the earth's surface. Part II: Model and instrument comparison,” J. Appl. Meteor., Vol. 34, 1995, pp. 2426-2439.
 J. Davies, P. Kuhn, G. Duhamel, J. Binyamin and K. Runnalls, “An ultraviolet (290-325 nm) irradiation model for southern Canadian conditions,” Physical Geography, Vol. 21, No. 4, 2000, pp. 327-344.
 P. M. de F. Forster and K.P. Shine, “A comparison of two radiation schemes for calculating ultraviolet radiation,” Quart. J. Roy. Meteor. Soc., Vol. 121, 1995, pp. 1113- 1131.
 W. J. Wiscombe and J. H. Joseph, “The range of validity of the Eddington approximation,” Icarus, Vol. 32, 1977, pp. 262-377.
 J. Lenoble, “Atmospheric radiative transfer,” A. Deepak Pub., Hampton, Va., USA, 1993, pp. 176.
 C. Erlick and J. E. Frederick, “Effects of aerosols on the wavelength dependence of atmospheric transmission in the ultraviolet and visible: 1. A “single-scattering-sepa- rate”delta-Eddington model,” J. Geophys. Res., Vol. 103, 1998, pp.11465-11472.
 D. Lubin, E. H. Jensen and H. P. Gies, “Global surface ultraviolet radiation climatology from TOMS and ERBE data,” J. Geophys. Res., Vol. 103, 1998, pp. 26061- 26091.
 T. Koskela, P. Tallas and E. Kyr?, “Measured and modeled UV-B spectrum compared with some atmospheric parameters,” In: Atmospheric Radiation,” K.H. Stamnes, ed., Proc. SPIE., Vol. 2049, 1993, pp. 296-306
 J. Zeng, R. McKenzie, K. Stamnes, M. Wineland and J. Rosen, “Measured UV spectra compared with discrete ordinate method simulations,” J. Geophys. Res., Vol. 99, 1994, pp. 23019-23030.
 B. Mayer, G. Seckmeyer and A. Kyling, “Systematic long-term comparison of spectral UV measurements and UVSPEC modeling results,” J. Geophys. Res., Vol. 102, 1997, pp. 8755-8767.
 E. Leontyeva and K. Stamnes, “Estimations of cloud optical thickness from ground-based measurements of incoming solar radiation in the Arctic,” J. Climate, Vol. 7, 1994, pp. 566-578.
 P. M. de F. Forster, “Modelling ultraviolet radiation at the earth's surface. Part I: The sensitivity of ultraviolet irradiances to atmospheric changes,” J. Appl. Meteor., Vol. 34, 1995, pp. 2412-2425.
 E. Pachart, J. Lenoble and C. Brogniez, “Consistency tests on UV spectral irradiance measurements using modeling and a broadband instrument,” J. Geophys. Res., Vol. 105, 2000, pp. 4851-4856.
 Atmospheric Environment Service (AES), “Canada’s National Environmental Indicator Series: Stratospheric ozone depletion,” Environment Canada, Downsview, Ontario, Canada. SOE Bulletin, No. 99-2, 1999.
 J. B. Kerr and C. T. McElory, “Evidence for large upward trends of ultraviolet-B radiation linked to ozone depletion,” Science, Vol. 262, 1993, pp. 1032- 1035.
 A. F. Bais, C. S. Zerefos and C. T. McElory, “Solar UVB measurements with the double and single-monochromator Brewer ozone spectrophotometers,” Geophys. Res. Lett., Vol. 23, 1996, pp. 833-836.
 J. A. Davies, “Correcting for stray light in Brewer spectroradiometers,” Environ. Technol., Vol. 17, 1996, pp. 421-426.
 D. L. Wardle and J. B. Kerr, “Scientific sponsorship statement for Brewer spectral data from Canadian stations,” WUDC documents, 1999.
 A. F. Bais, S. Kazadzis, D. Balis, C. S. Zerefos and M. Blumthaler, “Correcting global solar ultraviolet spectra recorded by a Brewer spectroradiometer for its angular response error,” Appl. Opt., Vol. 37, 1998, pp.6339-6344.
 U. Feister, R. Grewe and K. Gericke, “A method for correction of cosine errors in measurements of spectral UV irradiance,” Solar Energy, Vol. 60, 1997, pp. 313-332.
 J. R. Herman, N. Krotkov, E. Celarier, D. Larko and G. Labow, “Distribution of UV radiation at the Earth’s surface from TOMS-measured UV-backscattered radiances,” J. Geophys. Res., Vol. 104, 1999, pp.12059-12076.
 P. Wang, Z. Li, J. Cihlar, D. I. Wardle and J. Kerr, “Validation of an UV inversion algorithm using satellite and surface measurements,” J. Geophys. Res., Vol. 105, 2000, pp. 5037-5048.
 F. Cappellani and C. Kochler, “Temperature effects correction in a Brewer MKIV spectrophtometer for solar UV measurements,” J. Geophys. Res., Vol. 105, 1999, pp. 4829-4831.
 N. A. Krotkov, P. K. Bhartia, J. R. Herman, V. Fioletov and J. Kerr, “Satellite estimation of spectral surface UV irradiance in the presence of tropospheric aerosols: 1. Cloud-free case,” J. Geophys. Res., Vol. 103, 1998, pp. 8779-8793.
 J. L. Michalsky, “The astronomical almanac's algorithm for approximate solar position (1950-2050),” Solar Energy, Vol. 40, 1988, pp. 227-235.
 K. Stamnes, S-C. Tsay, W. J. Wiscombe and K. Jayawerra, “Numerically stable algorithm for discrete ordinate method radiative transfer in multiple scattering and emitting layered media,” Appl. Opt., Vol. 27, 1988, pp. 2503-2509.
 J. H. Joseph, W. J. Wiscombe and J. A. Weinman, “The delta-Eddington approximation for radiative flux transfer,” J. Atmos. Sci., Vol. 33, 1976, pp. 2452-2459.
 R. J. Paur and A. M. Bass, “The ultraviolet cross-sections of ozone: II. Results and temperature dependence” In: Atmospheric Ozone Proceedings of the Quadrennial Ozone Symposium, Edited by C. Zerefos and A. Ghaz, Kalkidiki, Greese, Reidel Publishing, 1985, pp. 606-616.
 L. Elterman, “UV, visible and IR attenuation for altitudes to 50 km,” Air Force Cambridge Research Laboratories, Environmental Research Paper, No. 285, 1986, pp. 1-59.
 E. P. Shettle and R. W. Fenn, “Models for the aerosols of the lower atmosphere and the effects of humidity variations on their optical properties,” Air Force Geophysics Laboratory, AFGL Technical Report 79-0214, Environmental Research Papers, No. 676, Bedford. Massachusetts, 1979.
 F. X. Kneizys, E. P. Shettle, L. W. Abreu, J. H.Chetwynd, G. P.Anderson, W. O.Gallery, J. E. A. Selby and S. A. Clough, “Users guide to LOWTRAN 7” Air Force Geophysics Laboratory, Bedford. Massachusetts, Technical Report 88-0177, 1988.
 J. Binyamin, J. Davies and B. McArthur, “UV-B cloud optical properties for Canada,” Int. J. Climatol., Vol. 30, 2010, pp.1246-1255.
 D. E. Bowker, R. E. Davis, D. I. Myrick, K. Stacy and W. T. Jones, “Spectral reflectance of natural targets for use in remote sensing studies,” NASA reference publication 1139, NASA, Langley Research Center, Hampton, Virginia, 1985.
 J. E. Hay and D. I. Wardle, “An assessment of the uncertainty in measurements of solar radiation,” Solar Energy, Vol. 29, 1982, pp. 271- 278.
 N. A. Hughes, “Global cloud climatologies: A historical review,” J. Appl. Meteor., Vol. 23, 1994, pp. 724-750.
 B. G. Gardiner, A. R. Webb, A.F. Bais, M. Blumthaler, I. Dirmhirn, P. Forster, D. Gillotay, K. Henriksen, M. Huber, P.J. Kirsch, P.C. Simon, T. Svenoe, P. Weihs and C. S. Zerfos, “ European intercomparison of ultraviolet spectroradiometers,” Environm. Technol., Vol. 14, 1993, pp. 25-43.
 A. F. Bais, B. G. Gardiner, H. Slaper, M. Blumthaler, G. Bernhard, R. McKenize, A. R. Wedd, G. Seckmeyer, B. Kjeldstad, T. Koskela, P. J. Kirsch, J. Gr?bner, J. B. Kerr, S. Kazadzis, K. Leszczynski, D. Wardle, W. Josefsson, C. Brogniez, D. Gillotay, H. Reinen, P. Weihs, T. Svenoe, P. Eriksen, F. Kuik and A. Redondas, “SUSPEN intercomparison of Ultraviolet Spectroradiometers,” J. Geophys. Res., Vol. 106, 2001, pp. 12509-12525.
 O. Meinander, S. Kazadzis, M. Blumthaler, L. Ylianttila, B. Johnsen, K. Lakkala, T. Koskela, and W. Josefsson, “Diurnal discrepancies in spectral solar UV radiation measurements,” Applied Optics, Vol. 45, No. 21, 2006, pp. 5346-5357.
 J. A. Davies and D.C. McKay, “Estimating solar irradiance and components,” Solar Energy, Vol. 29, 1982, pp. 55-64.
 J. A. Davies and D.C. McKay, “Evaluation of selected models for estimating solar radiation on a horizontal surfaces,” Solar Energy, Vol. 43, 1989, pp.153-168.
 G. Norsang, L. Kocbach, W. Tsoja, J.J. Stamnes, A. Dahlback and P. Nema, “Ground-based measurements and modelling of solar UV-B radiation in Lhasa, Tibet,” Atmospheric Environment, Vol. 43, No. 9, 2009, pp. 1498-1502.
 B. Chertock, R. Frouin and C. Gautier, “A technique for global monitoring of net solar irradiance at the ocean surface. Part II: Validation,” J. Appl. Meteor., Vol. 31, 1992, pp. 1067-1083.
 T. J. Wang, K. S. Lam, Q. Liu and T. K. Chan, “Assessment of long term UV radiation measured by the Brewer spectrophotometer in Hong Kong during 1995-2005,” Atmospheric and Climate Sciences, Vol. 1, No. 1, 2011, pp. 9-17.