عنوان مقاله [English]
Despite the large extent of the areas affected by 120-day Sistan winds, Zabul region with specific topographic location has the highest and the most severe storms in the east of the country. In order to identify and analyze the dust pattern of the Zabul region and to distinguish it from other parts which are affected by the famous 120-day winds of Sistan, environmental databases; dust codes, and NCEP / NCAR database with a spatial resolution of 2.5× 2.5 degree and latitude longitude of sea level pressure data corresponding to the peak days of dust during the period from 1987-2016 were used. In order to extract atmospheric patterns of dust events on sea level pressure data, cluster analysis was performed in MATLAB software. Finally, four patterns were extracted and for each pattern one day which has the most correlated with other days was selected as the representative day of that pattern. Out of four patterns the dominant pattern with the most frequent occurrence was selected, and July 13-16, 2016 was considered as the representative day for this dominant pattern. For this purpose, the synoptic maps of ground pressure, temperature, equatorial and jet flow in the lower layer of the atmosphere, wind field, and direction of the flow at ground level and the synoptic half instability of the air were plotted.
Results indicated that the Zabul area has the greatest potential for the production of dust due to the gradient of high pressure changes and also the presence of small-grained sediments of the rivers as well as wetlands and the locating in western margin of the low-pressure zone which has the thermal nature and the interaction of the low pressure with the high pressure which is called Turkmenistan high-pressure, Hindu Kush, northeast of Iran and north of Caspian sea. This low pressure in the lower layer of the atmosphere through the dust suction and counter-clockwise movement by passing on the sources of dust in the Zabul area prevented from the penetration to lower latitudes by the impact of the 120-day winds of Sistan and caused to further transportation of sand and dust particles to Afghanistan. Therefore, in regard to situation of Zabul in ratio to this low pressure, which is peaked in July, and distinguishes it from other areas affected by 120-day winds, special arrangements should be taken into account to reduce the intensity of dust storms.