Abstract
Mineral dust is one of the most important aerosol components in the Earth’s atmosphere. Desert aerosol constitute the main types of tropospheric aerosols whose optical property uncertainties are still quite important. In this study, we analyse the variability of aerosol optical depth (AOD), Angstrôm Exponent (α), Single Scattering Albedo (ω0) and aerosol radiative forcing (ARF) of desert aerosol recent measurements, for six AERONET sites covering the belt desert areas: Ouarzazate (Morocco), Tamanrasset (Algeria), El Farafra (Egypt), Mezaira (Unites Arab Emirates), Kuwait University (Kuwait), Dalanzadgad (Mongolia). The annual cycle of the aerosol optical depth dialy averages shows variable values due to the changeable weather and the Sahara source. The highests were recorded at the Sahara site (2.2 at Tamanrasset) and (2.9 at Kuwait-University). The spectral single scattering albedo SSA annual averages varies in the interval (0,8-0.95) indicating dominant scattering. Desert aerosol radiative forcing shows always a negative ARF with a maximums registred in July, -90 W/m2 at surface (Mezaira) and -26 W/m2 at the top of the atmosphere (Kuwait) that imply a general trend towards regional warming of the total column atmosphere with a maximum near +55 W/m2 observed in July at UAE.
Highlights
The sensitivity of climate models to the characterization of the continents aerosol particles needs more measurements
The Sahara desert is the important source of mineral dust in the Northern Hemisphere, it constitutes the first part of the belt desert area (Fig.1)
The high Aerosol Optical Depth (AOD), daily averages were registred at Ouarzazate, Tamanrasset, Mezaira, Kuwait- University, confirm the influence of the desert mineral dust near and in the Saharan emission sources
Summary
The sensitivity of climate models to the characterization of the continents aerosol particles needs more measurements. Many measurements campaign in desert zone were conducted in the past, the successful one with SAMUM consortium undertaken on May-June 2006 at Ouarzazate and Zagora (Morocco) close to Sahara gives very important description including chemical and physical properties of desert aerosol near ground and at different altitude levels during its transport [4]. Physical properties of the mineral dust as well as its chemical and mineralogical composition and state of mixing modify its influence on climate and atmospheric chemistry [7]. The short residence times in the atmosphere (days to weeks) and the large variability in composition and particle size distribution (wide range of sources) contribute of both natural (primarily sea salt and desert dust) and anthropogenic (primarily combustion of biomass and fossil fuels) aerosol disseminations.
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