عنوان مقاله [English]
Background and objectives: The occurrence of dust storms as a global threat poses annually a lot of financial and human losses to the country. Hence, according to the topographic-climatic conditions and the significant increment in the dust storm occurrence frequency, investigation and survey to mitigate the harmful effects is inevitable.
Materials and methods: In this research, dust storms were evaluated based on the spatio-temporal frequency of 25 synoptic meteorological stations in western and southwestern Iran during the statistical period of 22 years (1995-2016). Daily Data were analyzed using eight observation points in the form of special codes using statistical methods. The average dust accumulation in the cluster and average monthly, annual, warm and cold periods was calculated and plotted using R software for all stations.
Results: The results of the annual survey of dusty phenomenon indicated that Abadan station had the highest number of days in the whole region with the average frequency of 16 days in year. Bostan, Sarpol-E-Zahab and Ahwaz are the most frequent. 63.02% of the outsider dust storms events which distributed from 9:30 to 18:30 local time. 83.47% of the local dust storms events at 3:30 local time, the highest frequency of dust storms in June and July is the lowest in November and December. Also, the percentage of local and outsider dust storms frequency during the statistical period showed that 74.94% of the dust storm days were outsider sources and 25.06% of the local sources. The average frequency of dust storm in the under studied area is 36 days in warm and cold period of the year recpectively. In all studied stations, most of the dusty days were related to the warm period.
Conclusion: Whatever the disturbance of a dust wave originates from its original source, its intensity decreases. Therefore, it can say that the primary sources of dust phenomena majority of the under studied area, are such as Iraq, Saudi Arabia, Syria, and North Africa deserts. Investegition of spatial pattern showed
Dust storms were increased from the north to the south. While along west towards the east, it is in the Quadratic polynomial form. As a result, dust storm occurrence frequency increased from west to the east, and then it decreas towards the east. Zagros Mountains positioning, which run northwest-southeast through western Iran prevents dust storms from entering those area like a dam. Also the offset of this phenomenon is more time-consuming compare to other regions.