Consistency of dimensional distributions and refractive indices of desert dust measured over Lampedusa with IASI radiances

Abstract. In the context of the ChArMEx campaign, we present here some results concerning the quantitative comparison between simulated and observed radiances in the presence of atmospheric desert dust, between June and July 2013 in the southern Mediterranean Basin, in the air mass above the island of Lampedusa. In particular, comparisons have been performed between radiances as observed by the Infrared Atmospheric Sounder Interferometer (IASI) and those simulated using the σ-IASI-as radiative transfer model, which takes into account aerosol extinction effect through a set of fast parameterizations. Simulations have been carried out using different sets of input complex refractive indices, which take into account the parent soils of the aerosols. Their accuracy also relies on the quality of the characterization of desert dust microphysical properties, achieved through direct measurements in the ChArMEx experiment. On the one hand, the fact that the model can ingest such a variable input proves its feasibility. On the other hand, this work goes through a direct validation of different refractive index sets for desert dust in the thermal infrared, and pursues an assessment of the sensitivity of IASI data with respect to the dimensional distribution of desert dust particles. Results show a good consistency between calculations and observations, especially in the spectral interval 800–1000 cm⁻¹; further, the comparison between calculations and observations suggests that further efforts are needed to better characterize desert dust optical properties in the shortwave (above 2000 cm⁻¹). Whatever the case, we show that it is necessary to properly tune the refractive indices according to the geographical origin of the observed aerosol.