Comparison of Models Used for UV Index Calculations

Koepke, Peter; Bais, Alkiviadis; Balis, D.; Buchwitz, Michael; Backer, H. De; Cabo, Xavier; Eckert, P.; Eriksen, P.; Gillotay, D.; Heikkilä, Anu; Koskela, Tapani; Lapeta, Bozena; Lityńska, Z.; Lorente, J.; Mayer, Bernhard; Renaud, Anne; Ruggaber, A.; Schauberger, Günther; Seckmeyer, Günther; Seifert, Péter; Schmalwieser, Alois W.; Schwander, Harry; Vaníček, Karel; Weber, Mark

doi:10.1562/0031-8655(1998)067<0657:comufu>2.3.co;2

Cited by 31 publications

(40 citation statements)

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“…Additionally, uncertainties in the input information also propagate through to uncertainties in derived irradiances. When input parameters are well known, the estimated uncertainty in modelled UVI is about ±5%, as discussed above from the study by Koepke et al (1998).…”

Section: Uncertainties Associated With the Uvi Modellingmentioning

confidence: 92%

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Towards closure between measured and modelled UV under clear skies at four diverse sites

et al. 2007

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Abstract. The purpose of this work is determine the extent of closure between measurements and models of UV irradiances at diverse sites using state of the art instruments, models, and the best available data as inputs to the models. These include information about aerosol optical depth (unfortunately not extending down as far into the UVB region as desirable because such information is not generally available), ozone column amounts, as well as vertical profiles of temperature. We concentrate on clear-sky irradiances, and report the results in terms of UV Index (UVI).Clear-sky data from one year of measurements at each of four diverse sites (Lauder -New Zealand, Mauna Loa Observatory -Hawaii, Boulder -Colorado, and Melbourne -Australia) have been analysed in detail, also taking account of different measurements of ozone, including satellite-derived values, as well as ground measured values, both from Dobson instruments and as retrieved from the UV spectra under study. Previous studies have generally focussed on data from a single site, and for shorter periods. As such, it is the most comprehensive study of its kind to date.At Lauder, which is the cleanest low altitude site, we obtained agreement between measurement and model at 5% level, which is consistent with the best agreement found previously. At Mauna Loa Observatory, similar agreement was achieved, but model calculations need to allow for reflections from cloud that are present below the observatory. At this site, there are occasional problems with using satellitederived ozone. At Boulder, mean agreements were similar but the dispersion around the mean was slightly larger, corresponding to larger uncertainties in the aerosol inputs to the model. However, at Melbourne, which is the only nonCorrespondence to: J. Badosa (jordi.badosa@gmail.com) NDACC (Network for the Detection of Atmospheric Composition Change) site, there remain unexplained discrepancies.The measured values are significantly lower than the calculated values. We investigate the extent to which this discrepancy can be explained by incomplete knowledge of aerosol extinctions in the UV at this site. We conclude that further information about aerosol optical depth and single scattering albedo in the UVB region is needed to resolve the issues. For more polluted sites (the four considered locations show in general small aerosol load), the uncertainties in the aerosol input parameters would lead to less confidence on the modelling approach. At the three NDACC sites, the closure provided by the study gives confidence in both the measurements and our ability to model them. This study revealed a limitation in the use of PTFE diffusers when temperatures are lower than approximately 20 • C. It also documents the range of clear sky UVI values expected at these diverse sites.

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Section: Uncertainties Associated With the Uvi Modellingmentioning

confidence: 92%

“…For low sun conditions, agreement was within ±10% for wavelengths larger than 300 nm. Koepke et al (1998) intercompared UVI from six multi-scattering models. Agreements within 5% and 0.5 units in UVI were found for 80% of the conditions considered.…”

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confidence: 99%

Towards closure between measured and modelled UV under clear skies at four diverse sites

et al. 2007

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“…libRadtran [17] is a collection of C and Fortran functions and programs for calculation of solar and thermal radiation in the Earth's atmosphere (A. Kylling and B. Mayer, http:// www.libradtran.org). It has (also) been validated by comparison with other models [18] and radiation measurements [19].…”

Section: Outline Of the Methods For The Retrieval Of Spectrally Resolvmentioning

confidence: 99%

A New Algorithm for the Satellite-Based Retrieval of Solar Surface Irradiance in Spectral Bands

et al. 2012

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Accurate solar surface irradiance data is a prerequisite for an efficient planning and operation of solar energy systems. Further, it is essential for climate monitoring and analysis. Recently, the demand on information about spectrally resolved solar surface irradiance has grown. As surface measurements are rare, satellite derived information with high accuracy might fill this gap. This paper describes a new approach for the retrieval of spectrally resolved solar surface irradiance from satellite data. The method combines a eigenvector-hybrid look-up table approach for the clear sky case with satellite derived cloud transmission (Heliosat method). The eigenvector LUT approach is already used to retrieve the broadband solar surface irradiance of data sets provided by the Climate Monitoring Satellite Application Facility (CM-SAF). This paper describes the extension of this approach to wavelength bands and the combination with spectrally resolved cloud transmission values derived with radiative transfer corrections of the broadband cloud transmission. Thus, the new approach is based on radiative transfer modeling and enables the use of extended information about the atmospheric state, among others, to resolve the effect of water vapor and ozone absorption bands. The method is validated with spectrally resolved measurements from two sites in Europe and by comparison with radiative transfer calculations. The validation results demonstrate the ability of the method to retrieve accurate spectrally resolved irradiance from satellites. The accuracy is in the range of the uncertainty of surface Remote Sens. 2012, 4 623 measurements, with exception of the UV and NIR (≥ 1200 nm) part of the spectrum, where higher deviations occur.

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“…However, these parameters are not generally known. Koepke et al (1998) reported on a model benchmark to intercompare the performance of different models used for the prediction of UVIs based on information on aerosol and surface albedo as well as the total ozone content and the solar zenith angle. The agreement of the multiple scattering models was in the order of 5%, which shows the range of deviations due to the different calculation procedures, the assumed profiles and internal constants (e.g.…”

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confidence: 99%

Comparison of measured and modelled uv indices for the assessment of health risks

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Bais

et al. 2001

Meteorological Applications

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The World Health Organisation (WHO) and the World Meteorological Organisation (WMO) have jointly recommended that the UV Index (UVI) should be used to inform the public about possible health risks due to overexposure to solar radiation, especially skin damage. To test the current operational status of measuring and modelling techniques used in providing the public with UVI information, this article compares cloudless sky UVIs (measured using five instruments at four locations with different latitudes and climate) with the results of 13 models used in UVI forecasting schemes. For the models, only location, total ozone and solar zenith angle were provided as input parameters. In many cases the agreement is acceptable, i.e. less than 0.5 UVI. Larger differences may originate from instrumental errors and shortcomings in the models and their input parameters. A possible explanation for the differences between models is the treatment of the unknown input parameters, especially aerosols. Copyright © 2001 Royal Meteorological Society

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Comparison of Models Used for UV Index Calculations

Cited by 31 publications

References 12 publications

Towards closure between measured and modelled UV under clear skies at four diverse sites

Towards closure between measured and modelled UV under clear skies at four diverse sites

A New Algorithm for the Satellite-Based Retrieval of Solar Surface Irradiance in Spectral Bands

Comparison of measured and modelled uv indices for the assessment of health risks

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