A Synoptic Analysis of the Severe Cold Weather in North Khorasan Province

IntroductionClimatic elements create the climate of a region Air felt temperature differs in different climates. For example, the temperature may be 20° Celsius in a clear day without clouds in March, in a sense of coolness to the temperature region, while the same temperature in summer and in other regional temperatures is considered a cold and uncomfortable. Severe wind blows at below zero temperatures can quickly withdraw heat from the body, to the extent that it may cause freezing of the skin. Wind Chill Temperature index (WCT) is very important and it can be used as a general guideline for deciding clothing requirements in cold weather conditions. North Khorasan Province, is considered as one of the country's Agriculture and Tourism poles But, this region has consistently experienced severe cold weather over the years. Recent studies show that extremely cold weather has sometimes disrupted the lives of the people living in this region. Due to the region's natural resources, mining, tourism, and increasing population, it seems necessary to implement a project the on better utilization in this. This plan will succeed if the mechanism and the role of the major climate systems affecting the climate of this region are correctly identified. Therefore, this study aims to identify major synoptic patterns which create severe cold weather of North Khorasan Province and its arrival to the area, to identify and predict these patterns, and to be alert enough to prevent and reduce the potential damages.Material and methodsThe study of this region (North Khorasan Province) is primarily based on the equation of WCT (equation 1) days with severe cold weathers extracted. Values of less than 36 in this index indicate an extremly cold weathers. The most extreme case happens when the index value is -98. In this case, freezing occurs in 5 minutes.WCT= 74.35 +0.6215T –35.75 (V*0.16) +0.4275 T (V*0.16) (1)In order to calculate the frigid days, first, average daily temperature and wind speed (in 1984-2005) in sample stations of North Khorasan Province are received from the Meteorological organization. Then the temperature and wind are converted from Celsius to Fahrenheit and Nat to miles per hour respectively using the Wind-chill equation, Less than 36 days.To determine the synoptic patterns of severe cold weather in this study area, data related to the pressure, wind components (U&V) for different levels (surface, 500 and 850 hectopascal) is prepared. This data is sent daily to the National Center for Environmental Prediction United State (NCEP/NCAR). The excursion to the study to identify patterns was investigated. For more precise assessment of flow patterns in severe cold weathers time, using the components of orbital and meridional wind, relative vorticity maps were prepared. Vorticity maps by turning the air to determine the type, severity and determine the amount of spread low pressure system and high pressure was used.Results and discussionAmong the stations studied, the highest frequency is Quchan. In terms of severity of the cold is Quchan, Sarakhs station for months but the rest of December has the lowest intensity, but in the months after Quchan placed in other months, respectively Bojnourd and Mashhad are after Quchan.During the occurrence of extreme cold weather in the region, two synoptic patterns have been predominant. The blocking pattern is the most important model in terms of is the number of days and the second pattern is the deep trough in the event severe cold weathers are very effective in the region. The maps of extremely cold weather days indicate that blocking pattern has caused severe deviation of the west winds up and pulling them down to the low latitude. In depth trough pattern due to extreme cold weather there is a trough with the meridional development to the south which pulling down from high latitudes to low latitude, and this axis is located in East Iran. Trough is much deeper it would be more stable. In this model the study area located in the West of a deep trough, was derived from high latitudes which condition have been the cause of this severe cold weathers.In severe cold weathers has been occurred under this model, the advection of air from two sources that include high-pressure area located in West Lake Baykal, and a deep trough that high latitude air advection over the study area.ConclusionThis study shows that Quchan has experienced the highest occurrence of extreme cold weather. Bojnourd, Mashhad, and Sarakhs are in second place. In terms of severity of extreme cold weather, Quchan station is in the first place. In most cases the occurrence of severe cold weathers region, there was the main reason blocking system and a deep trough pattern of other cases as well as the establishment of a deep trough on the North of the study area and placed in the rear main reason is the occurrence of extreme cold weather. Between days with blocking pattern penetrate trough pattern of 17 to 25 degrees North is the variable that caused the temperature in the balance of 1000 and 500 hectopascal order of 5 to -10 and -25 to -40 on days with extreme cold weather pattern. Vorticity value in all the days of extreme cold weather due to this pattern was positive and on the region there was cyclonic circulation. According to the study area close to the source of exposure to the cold weather of Siberia and currents resulting from the tabs on the one hand and due to the high latitude, exposure to cold weather northern currents on the other hand, the region could be affected dynamical systems, thermodynamics and heat, are undergoing severe cold weathers.