Spectral effects of Saharan dust on photosynthetically available radiation in comparison to the influence of clouds

An important result was the parameterization of the spectral effects of different atmospheric conditions by power functions. The functions depend on the wavelength and the introduced normalization factors describing the effect of clouds and atmospheric dust on the magnitude of downward irradiance. The parameterization was used to investigate the influence of the spectral effects on photosynthetically available radiation. Their correct knowledge is important for many applications such as biology experiments and ecological modeling. The influence of spectral effects compared to clear sky case is in the order of few percents for all considered atmospheric cases. The spectral effects of different types of clouds reduce or enhance the photosynthetically available radiation up to 6.1% or 1.9%, respectively. Atmospheric dust modifies the influence of spectral effects of clouds on photosynthetically available radiation in dependence on the ratio of clouds to dust.