Synoptic Analysis of Productive Patterns of Winter Cold Wave's in Iran

1. One of the special temperature states in which extreme amounts of minimum temperature are observed, is the cold wave. The extreme cold waves due to the severity and sudden occurrence have an important impact on the ecosystems and human societies. There is a probability of occurrence of cold waves throughout the year and in each season, it creates its own special problems and damages. Because of the low angle of sunshine and the cold weather, these waves are stronger in winter and threaten the life of all living creatures.
They also play a decisive role in economic, environmental and developmental issues such
as road construction, damping and bridge construction, and can cause damage in various
sectors. The intensity and weakness of the cold waves depend on the complex synoptic
and dynamics factors, some of which are less well-known and their analysis using a
synoptic method can identify features such as the source, track, intensity and frequency
of pressure systems and helps to recognize the fundamental factors and their characteristics and to increase our understanding of winter cold waves.
2. Material and The study area in this research includes the whole country of Iran. Iran is a rugged country with an elevation average of about 1250 meters. roughness plays an important role in Iran's temperature; therefore, the temperature decreases wherever height increases. Iran’s average maximum temperature is 18 degrees Celsius and the average minimum temperature is 11 degrees Celsius.
In the present study, the effective patterns in creating winter cold waves in Iran were
identified using environmental to circulation approach. In order to achieve the specified
purpose in this study, two environmental and atmospheric databases were used.
Environmental data included the minimum temperature in winter between 1960 and 2011.
In this research, it has been attempted to be defined the cold Somehow so that the principle of its relativity is considered in different regions; accordingly and according to Alijani and Hooshyar (2008) and Massoudian (2013) researches, Two conditions for the
identification of cold waves were defined in the country. On the basis of the first
condition, days were considered as a day with a cold wave that standard Z score for the 10th percentile of minimum temperature data is less than or equal to -1/2. By defining
this condition, only very low temperatures were taken into consideration for each of the
7187 cells studied and the concept of relative coldness was considered for different
regions of the country. The second condition is the continuity of the cold weather for at
least 3 days; based on this condition, the systemic coldness from the local coldness (which
is caused by environmental factors or overnight cooling) is separated. According to these
conditions, cold days were identified on the ground and related synoptic systems were
investigated in different layers of the atmosphere.
3. In the first pattern, about 45 percent of the country's surface was affected by the cold
wave, and the average minimum temperature was -4.4 Celsius degrees. Based on surface
temperature maps in the northwestern part of the country, temperatures below -20 ° C
was observed. The main factor behind the formation of this pattern is the Azores high
pressure system, which has led to cold weather penetration from northern Europe to Iran.
Due to the formation of the second pattern, about 21 percent of the Iran’s surface was
affected by the cold wave. The average minimum temperature in the country is -2.9
Celsius degrees, which was the highest among other patterns. The lowest temperatures in this pattern were between -14 and -18 Celsius degrees that observed in the northwest, the central parts of the Alborz and northeast of the country.
In the third pattern, the daily average of minimum temperature is -2.5 Celsius degrees,
which is the lowest at the different patterns. In this pattern, 50 percent of the countrys
surface was affected by the cold wave. In this pattern, cold weather penetrates the
southern parts of the country and its impact was observed in many parts of the country.
On the day the representative, the Siberian high-pressure system is located at high
latitudes and in the central parts of Russia. The weakening of the Iceland low-pressure
and the displacement Azores high-pressure towards the westerner parts, has strengthened the Siberian high-pressure and increased its impact.
The minimum temperature average in the fourth pattern was -3.5 Celsius degrees and the cold air coverage in the country was 30 percent. Lowest temperature values were
observed in northern parts of the provinces of East Azerbaijan and Ardabil. This pattern
is somewhat similar to the first pattern, but contrary to the first pattern, there is a negative pressure anomaly in the northern regions of Europe and throughout Russia. The Siberian high pressure has shifted to the east and the European high pressure is located throughout the region, while in the first pattern, this high pressure was located in Western Europe.
The minimum temperature average in the Fifth pattern was -3.4 Celsius degrees and the
cold weather coverage in the country was 36 percent. In this pattern, the core of the
Siberian high-pressure is located in west of Mongolia, and the Icelandic low-pressure was
eastward movement and located in Scandinavia. This system has been located in large
parts of northern Europe and central Russia as well as parts of the Atlantic in Western
Europe. The expansion of this system and its displacement have caused more impact on
Siberian high-pressure.
4. Performing synoptic analyzes on atmospheric patterns showed that all the pervasive cold
waves in Iran were caused by the formation of massive high-pressure patterns in the
country, parts of the Middle East and Asia and South-East Europe. The position of the
two Siberian and Azores high-pressure systems has played a very important role in the
transfer of cold air to the northern latitudes towards the country. The deployment of a
polar low-pressure system in northern parts of Europe and Russia has led to the influx of
cold air towards the southern regions. The formation of specific patterns of the
intermediate layers of the atmosphere has had a significant effect on the creation and
intensification of the winter cold waves. So that the extreme winter cold waves are formed when Blocking systems have been established in Eastern Europe and their eastern Trough has been located on Iran.