Impact of desert dust events on short- and long-wave radiation at the surface over south-eastern Italy
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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 Ångström exponent (Å), 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 Å 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.
KeywordsDesert dust Irradiance measurements Dusty day identification Columnar aerosol properties
S. Romano has carried out this work with the support of a PhD fellowship from the Mathematics and Physics Department of the Salento University. This work has been supported by the European Community through the ACTRIS Research Infrastructure Action under the 7th Framework Program, ACTRIS Grant Agreement no. 262254. The authors would like to acknowledge the Barcelona Super-Computing Center for the provision of the DREAM8b DL data. The NOAA Air Resources Laboratory is kindly acknowledged for the provision of the HYSPLIT back trajectories. MODIS data were made available from the Goddard Laboratory sciences Data Center.
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