Statistical and Synoptic Analysis of widespread cold patterns in West of Iran

In this research using the standard score of minimum temperature data, the statistical characteristics of the widespread cold west of Iran and synoptic conditions their occurrence was analyzed for period 1992-2015. first by study of coldness events and their classification and selection a certain threshold for determination of widespread cold, 176-days of intensive cold in the four months of December, January, February and March extraction then using the data of Geo-potential height at 850 hPa and use of correlation method, extracted 5 Circulating pattern in creating this widespread cold. Among these patterns, the fourth pattern with a 105-day occurrence as the main pattern and the third pattern was detected only with 3-days as a random pattern. In terms of monthly and annual frequency, some patterns as the pattern the third in 2006 and fifth pattern in 1996 have occurred only in the month of January. Some others as the second pattern in 2006 and fourth pattern in more years of the study period and occurred every four months. The first pattern also of 2001 onwards and in months of January and February have occurred. Synoptic analysis representatives' days of patterns showed that the main factor creating the widespread cold in the west of Iran according to locating pressure centers, influence coldness from the North East and North West of Iran. Such that in the two case of the patterns from the north-west, the other two case from the northeast and one case from the north, cold air advection has happened into Iran.