A study on the vertical distribution of dust transported from the Tigris–Euphrates basin to the Northwest Iran Plateau based on CALIOP/CALIPSO data

Abstract The space-borne CALIOP lidar data has been used to better understand the dust transport mechanism from the Mesopotamian region to the atmosphere of Zanjan, a city in the Northwest Iran Plateau. The level 2 aerosol profile data product of the CALIOP has been studied for 142 overpasses during 2006–2018. The mean values of aerosol optical depth (AOD) and particulate depolarization ratio (PDR) at 532 nm, extracted from 142 cases, are 0.23 and 0.17, respectively. Moreover, 32 dust events (23% of all) have been recorded. For these cases, the mean values of AOD and PDR reach 0.53 and 0.21, respectively. The monthly-mean values of AOD and PDR confirm previous studies that dust particles are the dominant type of aerosols in the atmosphere of Zanjan, and their concentrations are remarkably increased in dry and warm months, especially between April to August. Based on the vertical profiles of PDR and extinction coefficients, the altitude range of about 1–3.5 km AGL is the most probable range of dust layer distribution in the studied area. Also, some dust events have been studied in more detail using the CALIOP data, sunphotometer data, ECMWF and HYSPIT meteorological models, and AOD product of the MODIS. Based on the results, dust particles originated from the Tigris–Euphrates basin, rise from the surface of Mesopotamia, move eastward, pass above the Zagros Mountains (the barrier between Mesopotamia and Iran Plateau), and finally reach the atmosphere of the studied area and cause dust events. It seems that it is the most probable mechanism of dust transport to the Northwest Iran Plateau.