عنوان مقاله [English]
نویسنده [English]چکیده [English]
Dust storms are among the most damaging natural disasters in the arid and semiarid regions of the world. This phenomenon as one of the environmental crises causes unfavorable environmental effects which result in the devastation of fields and gardens, the pollution of surface water, the expansion of deserts and dry areas, the creation of problems due to reducing the horizontal visibility, the occurrence of road accident, creation of barriers in railroads, respiratory and ophthalmic diseases, economic challenges and etc. therefore, the present study has the objective to statistically investigate and analyze the atmospheric circulation patterns causing the dust in Iran in a 30-year timeframe from 1979 to 2009. To do so, firstly, the number of the dusty days in Iran were identified and then the circulation patterns causing dust were designed. The databases and MATLAB software program with the array of 5328 * 155 with time on the rows and space on the columns were constructed and then, on the data array, the cluster analysis was conducted in the integration method and for the dusty days in Iran, four circulation patterns for geopotential height at 500 hPa were identified. The results indicate that in between seasons, the maximum of dust storms is in the summer and its minimum is in the winter and Tir (July) has had the most frequent storms, while Azar (December) has had the least frequent storms. The results obtained from the synoptic analysis show that at 500 hPa, the formation of dry air front over Iraq and Turkey which is the result of temperature contrasts of cold weather on Turkey and hot air over Iraq, is one of the factors of the transfer of the dust to deserts neighboring Iran. Further, low pressure areas of the borders of the Mediterranean Sea and Hijaz, the border of Iraq and Hijaz, the border of Iraq and Iran cause dust storms over Iran.