Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 4 2009 10.5194/acpd-9-17753-2009 http://www.atmos-chem-phys-discuss.net/9/17753/2009/ http://www.atmos-chem-phys-discuss.net/9/17753/2009/acpd-9-17753-2009.html http://www.atmos-chem-phys-discuss.net/9/17753/2009/acpd-9-17753-2009.pdf 17753 17791 2009-08-28 The impact of aerosols on polarized sky radiance: model development, validation, and applications C. Emde claudia.emde@dlr.de R. Buras B. Mayer M. Blumthaler Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, 82234 Wessling, Germany Sektion für Biomedizinische Physik, Medizinische Universität Innsbruck, Innsbruck, Austria Although solar radiation initially is unpolarized when entering the Earth's atmosphere, it is polarized by scattering processes with molecules, water droplets, ice crystals, and aerosols. Hence, measurements of the polarization state of radiation can be used to improve remote sensing of aerosols and clouds. The analysis of polarized radiance measurements requires an accurate radiative transfer model. To this end, a new efficient and flexible three-dimensional Monte Carlo code to compute polarized radiances has been developed and implemented into MYSTIC (Monte Carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres). Unlike discrete ordinate methods the Monte Carlo approach allows to handle the scattering phase matrices of aerosol and cloud particles accurately, i.e. without any approximations except the inherent statistical noise. The study presented in this paper shows that this is important, especially in order to simulate scattering by aerosols and cloud droplets in the ultraviolet wavelength region. The commonly used Delta-M approximation may cause large errors not only in the calculated intensity but also in the degree of polarization. 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