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Modeling UV sky radiance during twilight with taking into account the sunlight polarization

* Corresponding author. ** The work was partially supported by the Russian Foundation of Basic Researches by grant 05-05-65139. Abstract – Intensity and polarization of the solar light may be characterized completely by a vector of the four Stokes parameters. Therefore, accurate description of the radiation field in the Earth atmosphere requires a solution of the transfer equation in the unknown vector of the Stokes parameters. A simplified theory treats light as a scalar being equal to the radiance intensity only. Several studies have compared results of the accurate vector and simplified scalar radiative transfer models and have shown that the scalar treatment of light may have only restricted application. Though several observational conditions were exploited, an effect of polarization on modeling of UV radiance has not been investigated yet for twilight. The paper briefly presents a study of modeled UV radiance during twilight taking into account polarization. The intensity and the degree of linear polarization of the scattered UV radiance for two cases of the ground-based observations are discussed. In the first case, radiation incoming from the zenith for the solar zenith angles (SZA) from 90 to 96 is under investigation. Radiation in the solar principal plane for the beginning of twilight (SZA=90.1) was calculated in the second case.