Satellite -Synoptic Analysis of Widespread Snowfall in West Iran

Snow, as one of the important climatic-hydrological parameters, has a significant role in providing the world's water resources for industrial, agricultural and drinking purposes. At the same time, the dangerous consequences of heavy snowfall, avalanches, destruction of rural housing, disruption of road transport and communication and numerous other consequences that it has on the natural and human environment are significant for environmental scientists (Shakiba et al, 2015: 88). However, heavy snowfall, especially in the lowlands and lowlands of the middle latitudes, is unexpected and somewhat surprising. So that its continuation for a few days in these areas will have negative effects on practically all living standards of the residents of these areas (Hosseini, 2014: 101). In recent years, the use of satellite data in natural, hydrological and water resource management has grown significantly, and in this regard, MODIS sensor images due to acceptable spatial resolution and fast temporal retrieval power with a variety of bands. Spectral has put it in a good position. Also, due to the very high albedo of snow, it is possible to measure the level of snow cover using satellite data.

In the present study, the environmental approach to circulation was used to investigate the relationship between circulation patterns and heavy snowfall. Thus; first, the days of heavy snowfall in the studied stations were identified and then the synoptic patterns and atmosphere of the representative days were analyzed. In this regard, after receiving snow altitude data from the Meteorological Organization, heavy and widespread rainfall events were identified in three western provinces of the country, including Hamadan, Kurdistan and Kermanshah in the form of 16 synoptic stations, during the years 2000 to 2019. In order to study and analyze the synoptic patterns of days with heavy snowfall, by referring to the website of the National Center for Environmental Forecasting / Atmospheric Sciences (NCEP / NCAR), daily data on Sea Level Pressure (SLP), High Geopotential (HGT), zonal wind (UWND) and meridianal wind (VWND), air temperature (Air) and instability index (Omega) were extracted at the intersection of 2.5 * 2.5 and the relevant maps were drawn using GRADS software. Also, the area covered by snow was obtained from MODIS satellite images. MODIS data are of level1b type, which was calculated based on the parameters in the header, radiance and reflectivity. Reflective and thermal parameters for bands 4 and 6 were also used to apply the NDSI (Normalized Difference Snow Index).

After 20 years of study, 8 days were identified that heavy and heavy snow had fallen in the area. On February 4, 2011, in the middle of the atmosphere, a deep trough formed in the western Mediterranean and North Africa, with a strong positive vorticity. This situation has affected the study area.The location of this trough in the Mediterranean provides the moisture needed for snowfall from the Mediterranean Sea.

The results showed in the ground formed a powerful cyclone on Iraq and turbulent weather caused chaos for the region. This condition causes the air to cause accelerated the rise of the package and water vapor in the atmosphere with his quick ascent to the seed quickly convert hexagonal snow. Creates a pressure gradient that causes more than 12 HPa in the region was to create a strong front will be formed in the region. In the high latitudes of cold air and warm air in front of it is the lower latitude. Has caused more than 60 to 70 percent of the study area are covered by snow. A deep trough of cold air loss in middle levels at depths greater than 25 degrees latitude has been. With extreme vorticity and air along rapid ascent has been closed. NDSI index showed the results of actions by deploying the most weather systems has gone down snow-covered forests of western Iran.