dust storms are natural phenomena which occur in arid and semi-arid areas of the world. in this study, to evaluate the dust storms which occurred in mashhad over a period of 30 years (1981-2009), first, the number of days on which dust storms happened in mashhad (days with a wind speed greater than 15 m.s-1 and horizontal visibility less than 1000 m) were identified and counted for each month; ...
