| Gérard Thuillier1, Jean-Marie Perrin2, Philippe Keckhut1, Julien Jumelet1, Nadège Montoux1, Slimane Bekki1, and François Huppert2
(1) Service d'Aéronomie du CNRS, (2) Observatoire de Haute Provence
At Observatoire de Haute Provence, a set of instruments has been installed for providing measurements characterising the troposphere properties as the solar spectral irradiance on the ground, water (solid, liquid, or gaseous), aerosols, minor constituents such as ozone. These instruments are lidars, pyranometers (total and UVB), a daytime all sky camera, and a sunspectrometer. A study is presented concerning the influence of the cirrus on the solar irradiance budget on the ground. Comparison between pyranometers data and predictions by modelling based on radiative transfer processes, shows cases of overbrightness occurring in total and UVB solar irradiance on the ground, which are linked to the presence of cirrus as revealed by the daytime all sky camera images. However it exits also cases for which overbrightness in UVB does not occur. To understand the above observations, we have developed a model of scattering within a cirrus cloud. To explain the absence of overbrightness in UVB, it is necessary to include a carbonaceous core inside ice aerosols. |