Investigation of The Persian Trough and North Wind Roles in Intensifying Warm Period Extensive Dust Storm in western Iran

In this work, the role of the Persian trough and low-level jet (LLJ) in the north wind (Shamal) intensification were studied as the main cause of extensive dust storm (EDS) formation in the warm period of western Iran. In this regard, visibility reduction criteria of less than 1000m and the code of 06 (as a dust event) in more than 50 percent of the stations were refined in 21 stations in the west of Iran (Khuzestan, Ilam, and Kermanshah provinces) during 2000-2009. From a total of 346 dusty days, 28 specks of dust with duration of 1 to 12 days were detected, of which 20 are related to the warm period of the year (especially in the months of June and July). Further, the pressure patterns, potential vorticity and temperature, divergent field, wind vector and vertical profiles using NCEP/NCAR data and ERA-Interim data with 2.5 and 0.125 degrees resolution, respectively, in the range of 10N Up to 60N and 20E to 75E were extracted at all atmospheric levels. The results showed that the warm period dust storms in western Iran were related to the low-level pressure gradient in the Persian trough, which although it is a source of low-pressure monsoon, the strengthening of this low-pressure is due to the local and topographic factors of the western windward of Zagros. The deepening of this system by strengthening the northern wind is the cause of the formation of dust storms in western Iran. In addition, EDS rarely extend beyond 1000m due to the limitation of strong winds to low levels. The speed of these winds often exceeds 50 km/h. The severe nocturnal inversion, which generally extends at 400-450m height, causes an intense wind speed gradient, and developed a Jetstream, often overnight, at 250-350m height, that affected by the Blackheads heating system.