Phase Extraction of Synoptic Patterns with Positive North Atlantic Oscillation (NAO) and its Impact on the Winter Precipitation in Iran

North Atlantic oscillation effective pattern of variability of atmospheric general circulation in the extra-tropical Northern Hemisphere are the main climatic factors that control precipitation and temperature. They have huge economic and social impacts and also on the energy section, agriculture, industry and so son. Considering the importance of the oscillation on human activities and its relationship with climatic elements including precipitation, we identified and analyzed the positive phase of the oscillation and its subsequent relationship with winter rainfall in Iran. Data needed for this study included measurements of the amount of rainfall on a daily basis in synoptic stations, Climate and rain gauge data for the entire country in the years 1340-1388 were used, the sources of which are Meteorological Organization and the Ministry of Energy. By the use of multivariate statistical methods and Matlab, Surfer and Grads software the extraction of synoptic patterns. The results indicated five patterns extractions despite the stable condition in five patterns of the earth's surface in this phase, and the measurement of atmospheric precipitation that justifies this subject, was done by using patterns in 500 hpa level. Iran is located in the axis of cyclone related to the Mediterranean basin. Therefore, atmospheric precipitation in the whole country was dominated by the low pressure occurrence in winter.