1- PhD student of climatology, Faculty of Geographical Sciences, University of Kharazmi Tehran, Iran,
2- Professor of Climatology, Faculty of Geographical Sciences, University of Kharazmi Tehran, Iran, , bralijani@gmail.com
3- Professor of Climatology, Faculty of Geographical Sciences, University of Kharazmi Tehran, Iran,
4- Associate Professor, Department of Climatology, Faculty of Natural Resources, Kurdistan University, Sanandaj, Iran,
2- Professor of Climatology, Faculty of Geographical Sciences, University of Kharazmi Tehran, Iran, , bralijani@gmail.com
3- Professor of Climatology, Faculty of Geographical Sciences, University of Kharazmi Tehran, Iran,
4- Associate Professor, Department of Climatology, Faculty of Natural Resources, Kurdistan University, Sanandaj, Iran,
Abstract: (366 Views)
In this research, the most important synoptic patterns of widespread snowfall in the eastern half of Iran have been investigated. For this purpose, the current weather code data and snow depth of synoptic stations in the eastern half of the country during the statistical period of 1371-1400, for the months of October to March, were received from the country's meteorological organization. In order to investigate widespread snowfall, the days when more than 70% of the studied area saw snowfall at the same time were extracted as a widespread day. In order to perform synoptic-dynamic analysis of widespread snowfall in the eastern half of Iran, the classification method using cluster analysis was used and the maps of the representative days including atmospheric temperature, moisture flux, geopotential height, vorticity, front formation, jet stream, omega index and orbital and meridian wind data were drawn. Trend analysis was also performed using the Mann-Kendall test. The results showed that 3 patterns justify the snow cover in the studied area. These patterns are: high pressure in Siberia and central Europe-low pressure in eastern Iran, high pressure in western Iran-low pressure in Sudan, high pressure in central Europe-low pressure in eastern Iran and Afghanistan. In all the patterns in the middle of the atmosphere, the intensification of the meridian currents of the western winds along with the formation of high pressure and low-pressure centers has caused blocking in the path of the western currents and has provided the conditions for the ascent of the air. The concentration of the negative omega field and the relative positive advection, along with the location of the northeastern region of Iran in the left half of the outlet of the Subtropical Jet, have caused severe instabilities and widespread snowfall in the region. Also, the results showed that despite the absence of a trend in the number of snow days in the northeast of Iran, the number of snow days has decreased over time.
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