Impact of desert dust events on short- and long-wave radiation at the surface over south-eastern Italy

Abstract

Clear-sky short-wave (SW) and long-wave (LW) irradiance measurements at the surface were combined with AErosol RObotic NETwork (AERONET) sun/sky photometer aerosol products to study the desert dust impact on irradiance measurements at a Central Mediterranean site during the year 2012, by comparing measurements performed on dusty and dust-free days. Daily mean values of both the aerosol Angstrom exponent (A), calculated from the aerosol optical depths (AOD) at 440 and 870 nm retrieved from AERONET sun/sky photometer measurements, and the desert dust loading (DL) from the Barcelona Supercomputing Center Dust REgional Atmospheric Model (BSC-DREAM8b) were used to select dusty days. In particular, we have identified as dusty days the ones characterized by A values less than 0.9 and DL values larger than 0.5 g m−2. The desert dust events occurred from March to September during the analyzed year, in which we have identified 30 and 96 clear-sky dusty and dust-free days, respectively. The daytime SW and LW downward fluxes (FDN) on average decreased by 8 % and increased by 3 %, respectively, on the dusty days with respect to the dust-free ones. These flux variations were associated with an average increase of 40 % of the AOD at 440 nm and an average decrease of 39 % of the fine mode fraction (η) at 500 nm. The daily means of SW- and LW-FDN were reasonably correlated with the corresponding AOD and η values on the dusty days, revealing that the increase of the coarse mode particle contribution was mainly responsible for the flux changes. Conversely, both the SW- and the LW-FDN values were not correlated with the corresponding AOD and η values on the dust-free days.