Abstract:
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 was categorized 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.
Machine summary:
Based on synoptic data, Omidvar (2005) found that severe dust storms in Yazd province occur mostly in April and May. Ekhtesasi (2004) studied storm potential in the Yazd-Ardakan plain and presented a storm rose and storm drift potential to indicate the source areas of dust and sand during a dust storm.
It can be very effective in recognizing direction and frequency of an area’s severest winds, but it does not provide usable criterion for stormy and dusty wind analysis, since most stormy winds blow with a velocity beyond the threshold rate for lifting and transporting particles which subsequently create dust storms.
It shows the wind erosion power and relative velocity of sand transport in different directions.
1. Study area In this research, anemometer data from the Tehran-Mehrabad synoptic station during a statistical period of about 47 years (1961-2007) was used to draw the wind, storm, and sand roses.
This software can draw a sand rose and analyze it statistically using anemometer data from a meteorological station and the wind erosion threshold velocity of different faces in the station environment.
1. Drawing and analysis of seasonal and annual wind rose Analyzing the anemometer data from the Tehran-Mehrabad synoptic station showed that for about 34.
As can be seen, data from more than 151903 hours of monitoring was used to draw the wind, storm, and sand roses of the region.
Figure 3 shows the annual and seasonal sand roses of the Tehran-Mehrabad stations based on the anemometer data of a statistical period of 47 years and drawn according to the minimum threshold velocity (6.