عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The polar vortex is dominated by the dynamic of winter circulation in the lower seam, and the middle and upper parts of the windsurf, the most important feature of the weather, the presence of extreme winds at the outer edge, and low temperatures in the vortex area. In Iran, the temperature and precipitation conditions are controlled by polar water and high pressure. Whenever the axis of polar vortex from 40 to 50 degrees eastward deepens and extends to southern latitudes, the country's rainfall will be widespread and more intensive. Stack deployment in the west of the Black Sea and Eastern Europe will increase with precipitation and decline. The temperature is in the country. Determining the effect of atmospheric circulation on precipitation and temperature is one of the most important dynamical and synoptic meteorological goals. The study of the displacement of polar velocities and the strengthening and weakening of the polar waters can provide long-term predictions. In this study, using the data of the mean sea level pressure and the height of different pressure levels from 500 hPa to 010 hPa within the northern hemisphere, it was tried to use a daily rainfall data in October 2015 to investigate a flood event in the southwest region of Iran. It was analyzed with polar velocity changes. With the spread of polar fissures to southern latitudes along the lengths of 40 to 50 degrees, the establishment of a strong heap on the Black Sea, the East and the Mediterranean Sea, the presence of strong winds at the outer edge of the Dao, which leads to the capture of cold air within the vortex, Winds that bring humidity and heat from lower latitudes to Iran and the presence of tangible temperature conflicts between the western strip of Iran with higher latitudes can be deduced. Polar fence strengthening in the period from October 26 to 29, 2015 has a significant impact on rainfall increase in the studied area had.
Materials and Methods
In this research, the required data are taken from the NCEP / NCAR archive. These data are available from the CDC REANALYSIS Internet site in the form of netcdf, at a time interval of 6 hours and a 2.5-degree step along the latitude and longitude, all points on the planet from 90 to 90+ degrees latitude and zero to 357.5 degrees longitude. The data include the mean sea level pressure, temperature, geopotential elevation, daily precipitation data of western stations of the country, and wind pattern vector. Available files, each containing one-year data, are converted to text files by the ncdump command, which is one of the pcgrads executable commands. In this research, the ncread command was used in the programming language for converting data into text files, then using the average mean sea level pressure patterns, the geopotential height of the middle and upper levels of the atmosphere (500 and 050 hPa), the wind pattern vector The 200hp level, the 500hp temperature pattern, and the daily rainfall data of the western stations of the country in October 2015, examined the dynamics and dynamics of the meteorological conditions governing the precipitation system October 27-30, which resulted in flood events in the western part of Iran. To reduce the volume of content in this article, only analysis of October 28 and 29 is presented.
Results and Discussion
The study of the mean surface-to-ground and geopotential heights of different barley levels revealed that on October 27, the axis of the vortex crevices extends along the longitude of 40 to 50 degrees, and witnesses the presence of backs on the Black Sea and the East and the Mediterranean Sea. On Oct. 28, the stack and the waves are the widest. On October 29th, the nave has moved slightly toward the higher latitudes with its intensity. Considering that previous research has shown that whenever the axis of polar gravity from the southern latitudes along the longitude of 40 to 50 degrees is drawn, the precipitation rate in Iran increases and the stack is located in the east and center of Europe, The Black Sea and the East, and the center of the Mediterranean Sea, are also rising in Iran. Therefore, the results also indicate that conditions are favorable for precipitation.
A wind field survey at 200 hp in October 2015 showed that at this level, a polar jet flows along the meridian to the Black Sea and the Mediterranean Sea. There is also a tidal jet in the eastern Mediterranean and the western strip of Iran. The cold weather with these currents falls into the Mediterranean Sea, and warmer low latitudes also penetrate the southern winds of the area and make the situation more conducive to creating temperature conflicts in the region.
The results of the study of the temperature field at a 500 hp peak in October 2015 showed that on October 27-30, the Arctic Cooling Center covered vast areas of the poles, and the caverns of this cold air reached the southern latitudes on the Black Sea, the Mediterranean, and Siberia It has extended and influenced the country of Iran.
With the spread of polar fissures to southern latitudes along the lengths of 40 to 50 degrees, the establishment of a strong heap on the Black Sea, the East and the Mediterranean Sea, the presence of strong winds at the outer edge of the Dao, which leads to the capture of cold air within the vortex, Winds that bring humidity and heat from lower latitudes to Iran and the presence of tangible temperature conflicts between the western strip of Iran with higher latitudes can be deduced. Polar fence strengthening in the period from October 26 to 29, 2015 has a significant impact on rainfall increase in the studied area had.