واکاوی همدیدی بارش برف سنگین اردبیل و ارزیابی روند تغییرات فراوانی روزهای برفی با روش‌های ناپارامتری

Introduction
Snow as a climatic element due to the rainy season, its solidity, the area covered and the consequences it brings, deserves the study and attention of researchers and users of the environment. It has played a major and fundamental role, and in terms of microclimate, due to its weak heat conduction, it is considered a good protection for its vegetation against the cold (Kaviani, 2010). In the generally dry and semi-arid land of Iran, snowfall and snowy days have a great value, among which the amount of snowfall, the number of days of occurrence, its ratio with the days of precipitation, during the period of descent and its beneficial and harmful consequences, each of them can be the subject of There should be separate researches, while the average number of rainy days in Iran ranges from less than 10 to about 115 days, the maximum number of snowy days is on average in the northwest region and about 25 days a year (Alijani, 2016). On the other hand, the effects of heavy snowfall and avalanches, the destruction of rural homes, the disruption of road transport, communications, daily activities, and many other consequences on the natural and human environment have attracted the attention of some researchers. It is true that some of these researches have been in the field of temporal changes of snowfall in recent decades. Due to the fact that studying and knowing the factors disturbing human peace and well-being seems to be necessary and knowing the changes in the trend and factors that generate the atmosphere of natural phenomena can be a way forward, so in this study, the aim is to analyze the heavy snowfall in Ardabil from a synoptic point of view. And to investigate the trend of changes in the frequency of snowy days with non-parametric methods.
Methodology
This research has been carried out in order to investigate the synoptic heavy snowfall in Ardabil city with an environmental approach to circulation and to investigate the trend of changes in snowy days with non-parametric methods. In this regard, first the data related to the daily snowfall parameter for Ardabil synoptic station was received from the General Meteorological Department. Nonparametric Mann-Kendall method and sense estimator were used to analyze the time series trend of this variable.
Mann-Kendall test
In the Mann-Kendall test, the assumption of zero indicates randomness and the absence of a trend in the data series, and accepting the assumption of one indicates the presence of a trend in the data series. This test was first presented by Mann (1945) and then expanded by Kendall (1975) based on the rank of data in a time series and is calculated in two ways: 1- Statistical test (T) I-Kendall 2- Graphical test I- Kendall The calculation steps of this test are as follows (Zinali, 2015: 90).
Sense Estimator test
The sense estimator method, like the Mann-Kendall method, uses the difference analysis of observations of a time series. This method is based on calculating a median slope for the time series and judging the significance of the obtained slope at different confidence levels, and the steps to do it are as follows (Hajam et al., 1387: 161).


Conclusion
The purpose of this research is the synoptic investigation of heavy snowfall from an environmental perspective and investigating the trend of changes in snowy days with non-parametric methods in Ardabil. The results of the non-parametric Mann-Kendall test and sense estimator showed that the Test z value was -2.30 and the Qmed value was -0.931 at the confidence level of 95% and indicated a negative, downward and significant trend. Also, according to the results According to the analysis of satellite maps in the event of heavy snow on January 26, 1400, it was found that there are two high-pressure systems in the east and west of Iran, with their outward movement, they lead the nearby air mass towards the studied area, and the dominance of the high-pressure systems of Central Europe over the studied area. The study has caused the formation of weather conditions and has led to the stability of the air and its subsidence. This system has played a very prominent role in the transfer of cold air in the northern latitudes, and in addition, in the western part of Iran, it has formed a trough of atmospheric conditions in such a way that before the axis of the trough, the convective strengthening in the upper levels of the atmosphere leads the flow of cold northern winds to the lower latitudes. And especially the west of Iran. Due to the location of the studied area in the front part of the landing axis of the ship and the strengthening of the divergence in Wardspahr, the values of Tavai have become positive and the weather condition has become unstable. The movement of the westerly winds in the aforementioned nave channel has caused the moisture of the Black Sea and the Mediterranean Sea and its flow towards the studied area. On the other hand, the intensification of the wind speed up to 35 meters per second in the atmosphere of the studied area has fueled atmospheric disturbances, as well as the influx of cold currents. North, a cold air mass has condensed in the Naveh axis in the northwest of Iran and has lowered the surface temperature of the studied area to -2 degrees Celsius. The rule of cold air over the northwestern part of Iran has also reduced the thickness of the atmosphere and caused the contraction of the atmosphere. The results of this research are also aligned with the results of other researchers, such as Saleh and Eskandari (2012) and Dargahian and Alijani (2016), pointing to the role of deep troughs in the northwest of Iran, which play a very important role in the transfer of cold air from northern latitudes towards Iran. had. Also, Emininia et al. (2009), in the study of changes in heavy snowfall in the northwestern region of the country, pointed out that heavy snowfall in all stations and during the common statistical period had high fluctuations and a decreasing trend.