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This work will present aerosol size distributions measured in a Saharan dustplume between 0.9 and 12 km altitude during the ACE-2 campaign1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope  of sensitivity studies considering varied input parameters like solar zenith angle,  scaled total dust optical depth, tropospheric standard aerosol profiles and particle  complex refractive index. The results indicate that the large particle fraction has  a predominant impact on the optical properties of the dust. A single scattering albedo   of ω<sub><I>o</I></sub>=0.75–0.96 at 550 nm was simulated in the entire dust column    as well as 0.76 within the Saharan dust layer at ~4 km altitudeindicating enhanced absorption. The measured dust leads to cooling over the ocean butwarming over the desert due to differences in their spectral surface albedo and surface temperature.The large particles absorb strongly and they contribute at least 20% to the ARE in the dustyatmosphere.  From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median  diameter of ~9 μm and a column single scattering albedo of  0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal  parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles

Atmospheric radiative effects of an in situ measured Saharan dust plume and the role of large particles