A Synoptic Patterns Analysis of Winter Freezing in Iran

Frost and freezing is a weather phenomenon that occurs each year with irretrievable damages on disparate parts. The occurrence of this phenomenon in the mountainous region roads causes many problems to transportation part and road accident. The atmosphere circulation patterns play a major role in freezing occurrence, duration and spatial distribution especially in moderate zones. In this study, in order to analysing synoptic patterns of winter freezing in Iran, the daily data in 12 oclock UTC related to 500 hpa level and surface level pressure (SLP) during 1960-2000 in winter (December, January and February) was extracted in 2.5 degrees coincidence renovation data collection of National Center Environmental Prediction (NCEP). The selection limit consists of 408 points between latitude of 20°-60° north and longitude of 20°-80° east. In this article mode S and Varimax circulation was used to identify weather types. The related variable was merged using PCA and dimensions of matrix were reduced, and K-means method was used to classify weather types. Result shows that CP2, CP3, CP4 weather types characterized by the lowest temperature with northerly winds and highest advection occurs frost and freezing in Iran.