A Study on Dust Storms Using Wind Rose, Storm Rose and Sand Rose (Case Study: Tehran Province)

Sand and dust storms are natural events that occur widely around the world, mostly in dry and bare lands. Over the past decade a large part of Iran has been affected by this phenomenon, and Tehran has not been excluded from this event. Therefore, having knowledge of spatiotemporal frequency variations can aid us in future management and storm trajectory assessment. In this study the synoptic anemometric data of Tehran Mehrabad stations over the past 47 years were used. Annual and monthly wind and storm roses were drawn to determine the predominant wind direction. The primary results indicated that the prevailing wind direction is western, but in summer, it is southsoutheastern. According to the threshold wind velocity (6.5 ms-1) about 12% of recorded data wascategorized into the storm condition.. Results also indicated that western, northwestern, and southwestern winds have the three highest rates of sand drift potential (Dpt), respectively. The temporal variability of dust storms showed that between 1951 and 2005, the largest number of days characterized by dust and thunderstorms was observed in the spring and summer. The average number of dusty days in spring and summer was four d/m, and the fastest winds ranged from 40 to 49 m/s-1. An assessment of dusty days over the past five decades revealed that the average number of dusty days has significantly increased from 10 days to 80 days. It seems that cyclonic circulations in the Monsoon Trough together with regional winds in central Iran are responsible for the transmission of dust particles over central Iran. Results and data from this study can be helpful in determining and predicting the critical dust storm period and in forming management strategies in order to minimize aftermath impacts.