عنوان مقاله [English]
Synoptic patterns of the atmosphere is the main factor in the distribution of rainfall in time and place. It is one of the drought disasters every year to load frequency losses. This phenomenon as a result of severe and recurrent temporal-local atmospheric circulation patterns. Hence, the study and identification of synoptic patterns of the above phenomenon is inevitable. In this study, the first of the annual 17 rainfall station was selected in the West country standard time. After determining the time and place threshold rainfall, widespread wet year and drought in the area with the use of the SPI index was detected. Read on, for the purpose of identification and classification of synoptic patterns to agents of the creator of wet and dry periods of Principal Component Analysis and statistical Cluster Analysis was used. Then got the height of the geo-potential sea level pressure and level of 500 HP level from the National Center for environmental prediction website (NCEP/NCAR), and finally was analyzed by synoptic systems composite map related to each cluster. Results achieved show that for the dry period can be used to stack in the 500 HP level alignment in Eastern Europe because of the point sink and cold high latitude drooling into the area and prevent an air mass ascent. For the pattern of the Earth's surface can also be referred to a high-pressure cell that has been imported from Eastern Europe region and the atmospheric movements close to the Earth's surface under their influence. For more courses in related patterns align 500 HP level can be found in the Middle East to deep trough pointed out that Red Sea moisture into the region. On the other hand, ground level patterns consist a low-pressure flow on Zagros Mountains that make ready condition for climb and instability.