بررسی همدید وسیع ترین و مستمرترین یخبندان های شمال غرب ایران

Frost is one of the natural events whose early and late occurrence can affect different aspects of human life. Therefore, this research has been carried out with the aim of predicting the atmospheric factors of this phenomenon with an environmental approach. For this purpose, the environmental data related to the daily minimum temperature of ۲۰۰۱-۲۰۱۷ for ۹ synoptic stations located in Ardabil, Urmia and Tabriz provinces were obtained from the Meteorological Organization of the whole country and the days with temperature below ۰ degrees Celsius that cover ۴۰% of the studied area in were selected and using the ward hierarchical clustering method that was applied on the average sea level pressure maps related to ice days, the classification of the free days was done. In order to determine the representative of each class using scripting in the MATLAB environment, Lund's correlation was calculated between the maps of different days of each class of ۲ to ۵ groups with a coefficient of ۰.۵; And the days that had a correlation coefficient of ۰.۵ and the most similarity with the majority of days of that class were introduced as the representative of the group. After determining the representative day, atmospheric data was prepared from the Nova site and maps of sea level pressure, geopotential height, wind vector, temperature of ۵۰۰ hPa and atmospheric thickness were drawn in Gurdes software. The results of the ۴ patterns for ice days showed that the most effective systems on the northwest of Iran were high pressure systems in Siberia, low pressure systems near the Arctic and high pressure systems in Northern Europe, and the studied areas were located in the front of Faraz and the negative circulation of air brought stable conditions. In most of these patterns, the western winds that have moved in the polar ice channel have brought cold air from the northern latitudes into the atmosphere of the study areas and caused low air temperatures.

کلیدواژه ها:

تحلیل همدید ، یخبندان ، رویکرد محیطی به گردشی ، شمال غرب ایران