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Abstract:  
The purpose of this study is to analyze the nature and structure of Variation in atmospheric spring rainfall in Iran. For this purpose, the daily precipitation data from 573 synoptic, climatological and rain gage in a 50-year period (1961-2010) is extracted. After extraction rainy days inclusive, corresponding pressure data, was extracted using the programming capabilities in the GRADS software environment and have been identified by the cluster analysis of representative days and Iranian spring weather patterns in the MATLAB software environment. After the creation of the database for the determination of the rainy day, three criteria were considered; Daily precipitation of 1 mm and above, minimum continuity of two days and at least 50% coverage (without spatial continuity). The results showed that the highest amount of spring rainfall in Iran was due to the intense pressure changes the Caspian Sea East Turkey-low pressure, low pressure Saudi Arabia. While the most prevalent spring weather pattern of Iran, the Siberian-low-pressure Siberian strain of Saudi Arabia has been the low pressure of Sudan. So that by creating a strong pressure gradient on Iran and deployment Mediterranean landing deep in the atmosphere has led to instability in Iran. The status of moisture sources also indicates that the role of the Arabian Sea, the Persian Gulf, the Red Sea at 850 and 700 hPa, is clearly visible and detected in the spring humidity flux of Iran. In addition to providing the humidity of the coastal areas at the sea level, the Caspian Sea is one of the main sources of spring rainfall in the northwest and northeastern regions at 700 hPa; while the Arabian Sea plays the most role in the humidity flux towards the southern and western parts of Iran. Check the status of atmospheric vorticity showed the highest levels of instability in the atmosphere above the atmosphere, because of Westerly that has been accompanied by different pressure systems. In this regard, the maximum degree of divergence of the atmosphere occurred when the Siberian High Pressure was active and its tabs on Iran.
 
     
Type of Study: Research | Subject: Climatology
Received: 2018/12/24 | Accepted: 2019/06/16

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