statistical synoptic analysis of dust storm in khorasan razavi province (1993-2005)

dust storms are destructive climate phenomenon which damage farm, installations,roads,traffic and etc indemnifiable. this phenomena at dry and pertaining regions of the country as environmental perils, is effected by particular atmospheric condition.if the origin and extention of this phenomenon be recognized the damages can be decreased or counteracted.the studied about dust storm show thirteen – year statistical period (1993-2005). there was less than 5 days dust storm in a year in stations ghoochan, torbat heidarieh and kashmar, while there was more that 35 days in sarakhs sation. this research shows that main of there system which lead to dust storm follow synoptic conditions.on the level of the map in stormy day the low – pressure center closes around the southern part of khorasan and afgenistan .the central pressure of this low pressure, usually less than 1000 hecto-pascul. in contrast, the high pressure center closes on the caspian sea and usually in its southern part.the central pressure of caspian sea is more than 1015 hecto-pascal in most of the time.the center of cyclone closed in easthern and north eastern part of afganistan, at the level 850 hecto- pascal.it also, covers tongue cyclone of the southern part of khorasan.usually 144 geo- potential curve, especially during the storm blowing pass the northern part of the case study region. in contrast anticyclone closes cover the caspian sea and turkmanstan.it s height is more than 148 dca-meter geo - potential. so, the cyclone and the anticyclone cause strong winds speciall in southern part of khorasan razavi province, by making thermodynamic system and thermodynamic pressure