12. The phenomenon of dust, the most important environmental crisis in the dry lands

Semnan and Kashan province, including areas prone of the country are to dust storm occurrence in the North East and center. In this paper, in order to detect hurricane winds and corrosive agents, the two anemometers, Semnan and Kashan station was analyzed during a period of 44 years (1967-2010). The results of this study indicate that during the period under study, the occurrence of days with dust storms and Kashan province had decreased. The most common is occurrence of dust storms in spring (April-May). Using a soft wareWRPlot, annual wind Semnan and Kashan was drawn up. The analysis results depicted those winds up prevailing wind direction in Semnan, north and north east of Kashan. Also, using the soft ware, flower annual hurricane season in both provinces were drawn. The results of calculation and drawing Storm, which is based on wind erosion threshold velocity standard (6.5 meters per second), were prepared, Shows that in most of the northern Semnan and Kashan wind storms causing further blow to the North East. According to the annual flood flowers determined frequency, wind speed is less than the threshold velocity of wind erosion are, is equal to 73 percent. This indicates that the winds of Hurricane causing dust and manufacturers, 30% of all winds, theseareas arecomprised

dust storms, Rose, Storm, Semnan, Kashan