Abstract
To determine of location and type of blockings affecting the cold climate of Iran, daily geopotential height data of 500 hPa in 10-70 degrees north and 10-80 degrees east with grid point of 2.5 degrees in period of 1961-2010 were used. Blockings were identified by quantitative Tebaldi index on digital points. In the study area, there are three areas of blocking occurrence in Central Europe, Eastern Europe and Central Asia, respectively. The predominant type of blocking in these areas is of the Rex type, with the blocking and the cold storage being placed on top of each other in the middle levels of the atmosphere. If a Rex block is formed in Central and Eastern Europe, at the same time, a deep or cold trough is formed in Central Asia, and this sequence is normal in meridional atmospheric systems. Iran's precipitation is most closely related to the Eastern European blocking system and the Central Asian cold zone, and precipitation is increasing in most parts of Iran. However, if atmospheric high increases in Central Asia and omega-type blocking is formed, due to the increase in atmospheric altitude, precipitation will decrease in most parts of Iran. But if an omega-type blockage is formed in Central Europe, with the deepening of trough in the Balkans and the Black Sea, it is accompanied by precipitation in northwestern Iran, and if this type of blocking is formed in Eastern Europe, the concentration of precipitation is mainly in the Caspian region, from the Eastern Caspian to the northeast of Iran.
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