Study of the effect of low-level jets on genesis and transport of dust in the west and southwest of Iran

In this paper, using reanalysis ERA5 data and observational data, the effect of Low-Level Jet (LLJ) on dust in the west and south-west of Iran during the period 2007-2017 is studied. The vertical wind shear transfers the momentum from the jet level to the surface and then transfers dust from the sources, so to identify the LLJ besides the maximum wind speed, the vertical wind shear is also considered. Moreover, the horizontal and vertical range of LLJ, average of long term frequency of LLJ and monthly and seasonal frequency of dust are calculated in this study. The result of the comparison of observational data with ERA5 data shows that 10 m wind speed of ERA5 is larger than of observational data. Strong north to south pressure gradient due to the high pressure system over Iraq and Zagros and the low pressure system over the south-west of Iran, is the most important synoptic forcing that causes strong north and north-westerly and LLJ winds over the study area. Furthermore, region topography, land-sea breeze, weak surface tension over the Persian Gulf, temperature differences and special heat capacities between land and sea are other factors that form and affect the intensity of LLJ. The monthly wind speed distribution shows the maximum average wind speed 10 m/s in July and its minimum 2 m/s in January. The average height of the boundary layer varies from 2400 meters by days to 150 meters at nights, which is one of the main causes of LLJ. The highest frequency of dust in Ahvaz was in July 2009 with 30 days of dust