Atmos. Chem. Phys. Discuss., 13, 23895-23941, 2013
© Author(s) 2013. This work is distributed
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Aerosols optical and physical characteristics and direct radiative forcing during a "Shamal" dust storm, a case study
T. M. Saeed1, H. Al-Dashti2, and C. Spyrou3
1Science department, College of Basic Education, Public Authority for Applied Education and Training, Kuwait
2Department of Meteorology, Directorate General of Kuwait Civil Aviation, Kuwait
3School of Physics, University of Athens, Athens, Greece

Abstract. Dust aerosols are analyzed for their optical and physical properties during an episode of dust storm that hit Kuwait on 26 March 2003 when "Iraqi Freedom" military operation was in full swing. The intensity of the dust storm was such that it left a thick suspension of dust throughout the following day, 27 March, resulting in a considerable cooling effect at the surface on both days. Ground-based measurements of aerosol optical thickness reached 3.617 and 4.17 on 26–27 March respectively while Ångstrom coefficient, α870/440, dropped to −0.0234 and −0.0318. Particulate matter concentration of diameter 10 μm or less, PM10, peaked at 4800 μg m−3 during dust storm hours of 26 March. Moderate resolution imaging spectrometer (MODIS) retrieved optical and physical characteristics that exhibited extreme values as well. The synoptic of the dust storm is presented and source regions are identified using total ozone mapping spectrometer (TOMS) aerosol index retrieved images. The vertical profile of the dust layer was simulated using SKIRON atmospheric model. Instantaneous net direct radiative forcing is calculated at top of atmosphere (TOA) and surface level. The thick dust layer of 26 March resulted in cooling the TOA by −60 Wm−2 and surface level by −175 Wm−2 for a surface albedo of 0.35. Slightly higher values were obtained for 27 March due to the increase in aerosol optical thickness. The large reduction in the radiative flux at the surface level had caused a drop in surface temperature by approximately 6 °C below its average value. Radiative heating/cooling rates in the shortwave and longwave bands were also examined. Shortwave heating rate reached a maximum value of 2 °K day−1 between 3 and 5 km, dropped to 1.5 °K day−1 at 6 km and diminished at 8 km. Longwave radiation initially heated the lower atmosphere by a maximum value of 0.2 °K day−1 at surface level, declined sharply at increasing altitude and diminished at 4 km. Above 4 km longwave radiation started to cool the atmosphere slightly reaching a maximum rate of −0.1 °K day−1 at 6 km.

Citation: Saeed, T. M., Al-Dashti, H., and Spyrou, C.: Aerosols optical and physical characteristics and direct radiative forcing during a "Shamal" dust storm, a case study, Atmos. Chem. Phys. Discuss., 13, 23895-23941, doi:10.5194/acpd-13-23895-2013, 2013.
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