Effective cloud optical depth for overcast conditions determined with a UV radiometers

Authors

  • D. Serrano,

    1. Solar Radiation Group, Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain
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  • M. Núñez,

    1. Solar Radiation Group, Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain
    2. School of Geography and Environmental Studies, University of Tasmania, Hobart, Australia
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  • M. P. Utrillas,

    1. Solar Radiation Group, Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain
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  • M. J. Marín,

    1. Solar Radiation Group, Departament de Matemàtiques per a l'Economia i l'Empresa, Universitat de València, Spain
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  • C. Marcos,

    1. Solar Radiation Group, Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain
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  • J. A. Martínez-Lozano

    Corresponding author
    1. Solar Radiation Group, Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain
    • Correspondence to: J. A. Martínez-Lozano, Solar Radiation Group. Departament de Física de la Terra i Termodinàmica, Universitat de València, Campus de Burjassot, 46100 Valencia, Spain. E-mail: jmartine@uv.es

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ABSTRACT

Using a sky camera, episodes characterized by overcast low clouds in the Valencia region of Spain have been selected for analysis. One year of cloud optical depth data have been produced by inverting UV erythemal irradiance measured with a UVB-1 radiometer from Yankee Environmental Systems using the LibRadtran radiative transfer model. Measurement uncertainties, aerosol single scattering albedo and cloud properties are, in order of decreasing importance, the most important factors influencing the accuracy of cloud optical depth retrieval when using UV erythemal radiometers. Statistics for cloud optical depth show a highly skewed frequency distribution best described by a gamma distribution with highest frequency between optical depths of 10 and 15 and optical depths exceeding 100 at the extreme high end.

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