عنوان مقاله [English]
Understanding the conditions for the onset and end of glaciers is essential because of their importance in agriculture, transportation, and environmental issues to reduce damage. Meshginshahr country due to geographical location, topography and location in the path of migratory air masses, often witnesses the occurrence of frost and damage caused by these climatic elements.The severe dependence of the economy of the people of this region on agriculture necessitates a careful study of the beginning and end dates of this devastating phenomemenon. In this research, by considering the temperature of zero and below zero Celsius degrees, the start and end dates of glaciation in Meshginshahr city during the statistical period 2000-2019 have been extracted and classified. In order to better understand the contents, these dates have been adapted into the Julian calendar. The return period of each of the mentioned glaciers by SMADA software with a probability of 2, 3, 5, 10, 25, 50, 100 and 200 percent was calculated and the most appropriate statistical distribution was selected to survey the freezing. Finally, by extracting the synoptic maps related to the days of frost occurrence on the earth's surface, iso-altitude of 500 hPa, wind vector and temperature of the middle layers of the atmosphere, thickness of the atmosphere and level of 500 hPa, it was determined that the occurrence of frost on the earth's surface is related to the expansion of the high-pressure tongue of the migrant of Northern Europe and The central one is the high pressures of the North Caspian barrier and the expansion of the Siberian transect tongue. The level height of 500 hectopascals is also due to the placement in front and back of the western winds, and the maps of Tawai show the descent of the air mass most of the time. The results of this research indicate that in Meshginshahr city, the trend of autumn frosts is relatively stable and with a gentle slope towards the cold months of the year and spring frosts is moving towards the warm months of the year.
According to the time of occurrence, frost can be divided into two types: early and late. In the autumn season, the frost earlier than the usual time is called early frost, and in the spring season, the occurrence of frost later than the usual time is called late frost. These types of frosts affect the phenological stages of crops more than anything else, and every year they cause a lot of damage to farmers and gardeners due to frost damage to their crops (Hejazizadeh and Moghimi, 1386: 88). Therefore, the study of this period of the year, which is called the glacial period, in terms of its beginning and end, can be of great help to the officials of economic, civil, or even agricultural affairs and its planners, in such a way that some of their activities that are affected by this period Adjust it so that they don't get into trouble and crisis. On the other hand, the results of this research can help executive officials in planning for the sustainable development of the country and province. For this purpose, many foreign and domestic studies have been conducted in this field, including Idalo Gualuz et al. (2017), by investigating the causes of climate change in Spain, they investigated the effect of late spring frosts on the flowering phenology of trees. The results of the investigations show an increase in the minimum temperature in all weather stations compared to the base period. Meshkinshahr city, due to its location in the path of high-pressure migrants and cold fronts, mostly faces the phenomenon of frost in the spring and autumn seasons, and enough time is needed to harvest garden crops in the autumn season, and in the spring season, due to the regrowth of plants and Blooming of fruits should be provided in such a way that no damages are caused to the products. On the other hand, the transport sector of the studied area is the road connecting the province center to the cities of Garmi, Beile Sawar and Dasht Moghan, and the study of early and late frosts in the region is necessary to avoid damage to the economic sector of the province
After obtaining the required minimum daily temperature statistics for the mentioned years from Meshkinshahr meteorological station, it is necessary to determine the date of the first and last frost for the study and statistical analysis of each year. The method of obtaining these dates is that from the first of October of the solar year, the temperature was checked at least daily, and the temperature that reached the threshold of zero and below zero degrees Celsius was considered as the date of the first early autumn frost. Also, to determine the date of the last spring frost, from the end of spring, the minimum daily control temperature and the last day when the temperature was equal to zero or below zero were considered as the date of the last spring frost. Statistical information and data were calculated and analyzed using EXCEL (SPSS) software. In the following, the linear regression method (simple linear and polynomial) was used to analyze the change process of the mentioned glaciers. ) by drawing the polynomial trend on the ice time series, the increasing or decreasing periods of the ice can be studied during the time.
SMADA software was used to calculate the return period of the mentioned frosts, and the return period of frosts is 50, 66.7, 80, 90, 96, 98, 99, and 99.5 percent with the return period of 2, 3, 5, 10, 25 percent. 50, 100, 200 years were determined. Then the type of ice, both radiation and advection, was determined. Finally, for the purpose of synoptic analysis of the start and end dates of the autumn and spring frosts of the region under study, the maps of the earth's surface, the iso-elevation of the 500 hpa level, the wind vector (in a combined form), the surface temperature of 500 hpa and the thickness of the atmosphere (difference between the surface height of 500 and 1000 hPa) combined form) and finally the 500 hectopascal level maps were extracted from Grads software and analyzed.