Atmos. Chem. Phys. Discuss., 9, 17753-17791, 2009
www.atmos-chem-phys-discuss.net/9/17753/2009/
doi:10.5194/acpd-9-17753-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The impact of aerosols on polarized sky radiance: model development, validation, and applications
C. Emde1, R. Buras1, B. Mayer1, and M. Blumthaler2
1Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, 82234 Wessling, Germany
2Sektion für Biomedizinische Physik, Medizinische Universität Innsbruck, Innsbruck, Austria

Abstract. 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. The polarized downwelling radiation field is calculated for various aerosol types showing the high sensitivity of polarized ultraviolet radiances to the particle microphysics. Model simulations are compared to ground based measurements and found to be generally in good agreement. This comparison shows that there is a high potential to retrieve information about the aerosol type from polarized radiance measurements.

Citation: Emde, C., Buras, R., Mayer, B., and Blumthaler, M.: The impact of aerosols on polarized sky radiance: model development, validation, and applications, Atmos. Chem. Phys. Discuss., 9, 17753-17791, doi:10.5194/acpd-9-17753-2009, 2009.
 
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