تحليل سينوپنيك سيستم هاي گرد و غبار در غرب ايران

A Synoptic Analysis of Dust Systems at the West Part of Iran

Dust is an atmospheric phenomenon which has many unsuitable consequences to environments. In relation to location and climatic situation, Iran exposes too many local and synoptic dust storms at through the year. With regards to nearness of west part of Iran to deserts of Iraq and Arabian Peninsula, this part of the country generally exposes to sever dust storms. In this article we have studied the genesis and origin of dust systems in west part of Iran from 1983 to 1987. The hourly data of dust, visibility, relative humidity, rainfall, wind and other factors for 15 synoptic stations from west of Iran were utilized. So, weather maps in two levels of ground and 500 hpa layer were analyzed. Results of this study shows that the number of dust days and dust waves in June is very high in comparisons to the other monthes. Dezful station with average 137.4 days,during statistic period has had the most dusty situation. When Khoy with average 2.6 days has had the least dusty station. Also, results shows that the troughs and dynamic low pressures penetrate to zone when subtropical high pressure is absent or very weak. These systems in relation to situation sometimes produce dust and sometimes rainfall or both together but when the Azores high pressure is strong, thermal lows at the ground are producing. These lows play important roles in production of local dust storms. With regards to routes and location of troughs and cyclones in different days, the Syria desert, Nofoud desert in the north of Arabian Peninsula and northern of Sahara desert main roles in genesis of dust storms respectively. Thermal lows of Arabian Peninsula are effective when these pressure centers are going to near the west part of Iran or supported by a strong trough at the upper level. In other word, this phenomenon is happened when above mentioned systems changing into dynamic-thermal lows.