Abstract

The Middle East is one of the hot-spot regions that has reported the highest occurrence of dust storms. In this study changes in aerosol optical and radiative properties during dust storm over the Middle East on July 2009, was analyzed using retrieved Aerosol Optical Depth (AOD) from Simplified Aerosol Retrieval Algorithm (SARA) algorithm over study regions and ground-based observations from CIMEL Sunphotometer measurements at AERONET (AEronet RObotic NETwork AERONET) site at Kuwait University. Dust plumes captured well with the SARA AOD during dusty days. Maximum AOD values occurred on the 4 July in Kuwait, Ahvaz, Iran, the Persian Gulf, Baghdad and Riyadh where values of 1.44, 2.56, 1.07, 3.0, and 1.99 were recorded, respectively. The maximum aerosol volume size distributions (VSDs) at AERONET site occurred on dusty days and minimum VSDs on non-dusty days. The single scattering albedo (SSA) obtained higher values on dusty days compared to non-dusty days, for all wavelengths (440, 675, 870, and 1020 nm) at the AERONET site. The maximum SSA value of 0.99 occurred at a wavelength of 1020 nm, which is an indication of the dust aerosol. The asymmetry parameter (AP) obtained higher values at shorter wavelengths over the study period. The AP (AP-T) for both modes (fine and coarse) values were higher in the near infrared region than in the visible spectral region on both dusty and non-dusty days. The coarse AP (AP-C) values were higher in the visible spectral region than in the near infrared region on dusty days with the reverse being true on non-dusty days. The VSD, SSA, AP, and refractive index values on dusty days suggested that dust aerosols were predominant over anthropogenic aerosols in the study area. Effect of aerosol on Downward Surface Shortwave Radiation (ARFDSSR) on both dusty and non-dusty days ranged between -51 and -160 Wm−2 (average: -90 Wm−2) at the earth's surface. Effect of aerosol on Net Surface Shortwave Radiation (ARFNSSR) on both dusty and non-dusty days ranged between -39 and -122 Wm−2 (average: -69 Wm−2) at the earth's surface. Dust-induced turbid conditions caused significant extinction of 15–20%, in DSSR, resulting in an increase of 66% in aerosol radiative forcing (ARF) at the AERONET site at Kuwait University. The HYSPLIT back-trajectory analysis revealed that the air masses reached Kuwait from the western part of the Sahara Desert in northwest Africa and Saudi Arabia over the Middle East. Aerosol vertical profiles retrieved by the space-borne Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) reveal a well-mixed dust layer occurred over the study area. The aerosol types identified by CALIPSO in the near of the study regions include both dust and polluted dust, but dust aerosols were dominant over the anthropogenic (polluted) aerosols. The CALIPSO aerosol profile indicated a layer of thick dust extending from the surface to an altitude of about 6 km. The results of radiative forcing of dust storm in the Middle East show that mineral dust cause decrease of shortwave radiation and net radiation at the surface. Additionally the presence of mineral dust cause decrease of temperature at earth’s surface. So, dust directly influence the earth’s radiative budget and cause surface cooling.