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Bohloul Alijani, Bahram Molazadeh, Mohammad Saligheh, Mohammad Hossein Nassrzadeh,
Volume 1, Issue 4 (1-2015)

Climate is one of the important natural factors that affect all stages of life, particularly human exploitation. Selection of the type of clothing, housing, cultures, architecture, civil engineering, and settlements are influenced by climatic factors. It can be said that the climatic circumstances of the surface of the earth and atmospheric circulation patterns have an important role in shaping and organizing the environment (Alijani, 2009). In some cases, the normal weather conditions become abnormal and cause many damages, which are mostly catastrophes rooted in climatic changes, such as hail, frost, heat and cold waves, floods, storms and so on. Blizzard is one of the atmospheric phenomena, which happens as the result of snow combined with wind (15 meters per second), and low temperatures (below zero°C), and it causes severe losses.

Due to its special geographical location, Iran is placed in the transition region of the large-scale patterns of common tropospheric circulation, and is the intersectional place of the of extra-tropical and tropical circulation system. This feature along with its complex topography caused the land to have a considerable climatic diversity. The climatic diversity makes the various climatic phenomena to be observed with intensity, energy, and different frequencies, therefore, the climatic phenomena with high intensity always causes damage to natural resources and the human civilization. This undesirable phenomenon is called climatic risks. Since the West Azerbaijan Province is located in mountainous areas and high latitudes, the feature is triggered many climatic risks such as flood, hail, snow, snow storm, and so on. Therefore, snowstorm is one of such phenomena that have occurred every year or every few years due to the specific characteristics of the region and have caused damages in the fields of transportation, energy, livestock, closeness of schools and offices.

The purpose of this study is the statistical and synoptic analysis of snowstorm in west Azerbaijan province. Therefore, the data related to the present weather codes were collected during the period 1986 to 2009 from the National Meteorological Agency. The data related to the weather codes entered in Excel, and data related to the snowstorm were selected through Filter tool and isolation of codes related to the strong snowstorms (codes 37and39) and weak snowstorms (codes 36 and 38). Then the data related to the snowstorm was entered in SPSS, and the statistical analysis was performed. In the next step, three cases of the strong and common snowstorm (code 37 and 39) were selected for synoptic analysis. Then, the synoptic maps of the different layers of the atmosphere were selected as the samples for strong snowstorm for the days before the event of the phenomenon, the day of event, and the day after the event of the phenomenon by the using of the accuracy of 2.5 degrees from website. The study area has been selected in 10 to 80 degrees north latitude, and 15 to 90 degrees east longitude for identifying the patterns that affect West Azerbaijan Province. The data was received on wind speed and direction in digits from the National Center for Environmental Prediction. Then, the maps of the wind direction and speed were provided in Grads. Finally, the daily analysis and interpretation of pressure (500hPa at sea level), instability (700hPa level and the ground level), Earth's surface temperature, wind speed and direction maps for 700hPa level, and identification of patterns that have caused snowstorm in West Azerbaijan province were carried out. Statistical and synoptic analysis of snowstorm phenomenon in West Azerbaijan province during was performed in the period 1986 to 2009. To do this, using codes 36 to 39, which represent a variety of snowstorm (weak and strong), the frequency of snowstorm days on monthly and annual average, distribution of the snowstorm in the extracted stations, the frequency of strong snowstorms (codes 37and39), weak snowstorms (codes 36 and 38), all types of snowstorms (codes 36 to 39), and the frequency of storms in the station level were compared. Out of 322 snowstorms occurred during the period 1986 to 2009 in seven synoptic stations 108 have been determined as strong snowstorm and 214 as weak snowstorm. In order to analyze the synoptic snowstorm in West Azerbaijan province, in the first place, the strong snowstorms were identified, and then five of the strong and comprehensive storms were selected for the synoptic analysis. The snowstorms of choice are as follows: On 18 January 1986, on January 19, 2000, on February 7, 1992, on February 5, 1997, and on December 25, 1990.

For applying the study, pressure maps, Omega (700hp level at ground level), Earth's surface temperature, and wind speed and direction at 700hPa were analyzed, and patterns and conditions that are causing this phenomenon in the West Azerbaijan province were identified.

      In this study, to perform statistical and synoptic analysis of snowstorm in Western Azerbaijan province, the statistical data were examined during the period 1986 to 2009 from 7 stations, and the results of the statistical analysis showed that:

• Out of a total 322 snowstorm event days of 7 synoptic stations during the period 1986 to 2009, 108 and 214 days were strong and weak snowstorms, respectively.

• Review the annual and monthly snowstorm during the study period showed that the 1992, 1997, and 1989 with a total of 69, 29, and 25 days, as well as the 1999, 2006 and 2007 with 0, 1, and 1 day have the most and the fewest days of snowstorm, respectively. The statistical analysis showed that the snowstorm phenomena happened in January, February, March, April, November, and December. January had the most and April had the fewest snowstorms with 119 and 3 days, respectively. February with 39 days, and April and November, with the number 0 and 1 had the most and the fewest days of strong and constant snowstorms.

• Distribution of the snowstorms in the stations indicated that out of the studied seven synoptic stations, which had a great impact on the synoptic situation of the region, topography, and height, Sardasht-Maku station had the most, and stations of Khoy, Mahabad, and Orumiyeh by having no snowstorms had the fewest days of snowstorm.

• The results of the maps of the different levels of the atmosphere and Earth’s surface in the days before the storm, event day and the day after the snowstorm were selected for the snowstorm pattern, which indicated that the snowstorm in the winter due to low compliance pressure formed in the earth's surface with synoptic patterns of middle levels of the atmosphere have provided the conditions for the event, in a way that among the sample cases of the strong snowstorms occurred in the West Azerbaijan Province two circulation patterns were involved in the formation of natural hazards: The Caspian Sea low pressure pattern- Eastern Europe high pressure pattern and the north of the Black Sea low pressure pattern.

Hassan Lashgari, Farshad Pajoh , Mohammad Bitar, Farzaneh Jafari,
Volume 2, Issue 1 (4-2015)

The temperature as an indicator of heat intensity is one of the basic elements of knowing weather. The frost is a condition when the air temperature is less than 0 c Due to the geographical possition of Iran, spring is a season that plants resume a new life after leaving a pause in a periode of the growth. At the beginning of such a periode emerge of sudden cold cause loss bloom (in the case of openinig) or delay in a beginning of plant growth periode (Azizi,2002). Recentley with occuring climate chaos, one of the important climatic disasters which treats human and particularly different  areas of the country are cold waves and sever frosts that in some years covers large area of the country.

    Surface data including minimum daily temperature of the days of 29 to 30 and 25 to 26 of march of 2003 and 2005 in 9 meteorological synoptic stations in the area of north west of Iran in  table (1) was collected  from meteorology organization then the days of cold waves in the above mentioned time periode, were analyzed. In ordet to analyse the synoptic patterns, using ncep/ncar data, maps of sea level pressure ,combined of  geopotential height and vorticity and temperature advection  using Grads were drawn and analysed in the levels of 1000 to 500 hpa.
    As it mentioned, during the time period, 29 to 30 and 25 to 26 of the march in 2003 and 2005, 2 clod system  were located on the area of north west. In oeder to explain and analyze of  synoptic patterns of  mentioned period time, the absolute minimum temperature below 0 degrees celsius of stations in western Azarbayejan province were selected and maps of sea level pressure, combined of  geopotential height and vorticity and temperature advection  using Grads were drawed and analysed in the levels of 1000 to 500 HPA. 
     The results showed that in the time of occuring hazardous cold waves of  29 to 30 of march 2003 and 25 to 26 of march 2005 and analyzing the sea level map in the first day of cold wave with spreading the cold core high pressure  from the eastern Europe and its location on north and east north of the black sea and its pentration from north west corner of the country covered most of the areas of the country. 
    Analyzing the combined maps of geopotential height and vorticity in the levels of 1000 and 850 HPA in the first day of occurrence of  cold, generaly faced with huge anticyclonic development . But in the levels of 700 and 500 HPA , the under studied area was in the south trough of the obtained cold core of the low height locating in the cetral Asia. But on the day of cold peak, high pressure core was exactly located on the under the studied area . Also in the upper levels of atmosphere with locating the back of the trough cumulated  of cold air of upper width on the sea level high pressure centre while strengthening the lower levels anticyclonic flows, led to intensifying cold and frost in the west Azarbayejan province. 
Positive and negative vorticity maximum cells, also conformed the intensity cold circulation flows on the north half of the country in anticyclone and cyclone centers in order. Also analysing the temperature advection in the levels of 1000 to 500 HPA, direction and temperature intensity exactly followed geopotential height maps patterns. 
     Such that in the levels of 1000 hpA of the both cold wave analysed, the anticyclonic cold temperature adcection and northward is located on the north west of the Iran. In temperature advection maps of 29 and 30 march 2003 in 850 HPA in Azarbayejan province, the anticyclonic circulation is matches with sea level high pressure. But in the 2nd cold wave that’s occured on 25 and 26 march 2005, the north west area is between 2 antycyclonic circulation on Mediterranean and cyclon located on south of  Russia that the directions of temperature cold flows is completely north ward in this level. 
    In the temperature advection maps of 700 and 500 HPA, the Azarbayejan province is in the western edge of central Asia trough or south of Russia. 
    The results showed that with studying  atmospheric motions and synoptic systems which create cold flows, we can prevent of spring late  emergence cold wave destructive impact on agricultural products, energy consumption, and road accidentd by  forcasting of these atmospheric conditions.

Mahmoud Ahmadi, Hassan Lashkari, Parasto Azimi,
Volume 2, Issue 2 (7-2015)

Understanding the climate of a region as a first step and most immediate action is considered research for development projects Climatic phenomena such as floods every year irreparable damage to the soil, pastures, forests, urban and rural facilities, human and animal import Climatic phenomena such as floods every year irreparable damage to the soil, pastures, forests, urban and rural facilities, human and animal import. The first factor in causing flood is rainfall intensity that occurs at a certain time. Therefore necessary infrastructure projects, and one of the main issues in hydrological and hydro-climate is awareness of the occurrence and amount of rainfall, most likely for different periods.

     In order to implement the model of Synoptic convergent in this research and estimated probable maximum precipitation in the South West region of the Caspian

   1: The 1:50,000-scale Digital Mapping the location of all stations in the study area, Climatology, rainfall and hydrometric surveys in selected were identified on the map.

   2: The maximum instantaneous discharge rate of the highest daily rainfall stations selected surveys (1976-2011) are also studied.

   3: collection of the highest daily rainfall statistics selected stations, monthly and annual precipitation data for the period (1986-200),Facts about the daily atmospheric phenomena (cloud, wind speed, dew point temperature, air pressure) with an interval of 3 hours to 3 hours, Statistics continuing 12-hour maximum dew point of the surface (in degrees Celsius) and wind speed times (NAT) for the stations of Anzali, Rasht, Astara, Ramsar, Ardabil, Pars Abad For the first 10-day period, 10-day and 10-day return period for calculating the 50-year-old third, 80-year and 100-year and monthly statistics on the average pressure of the selected stations establishment station.

   4: Select the desired storm rainfall in 24 hours and 48 hours to obtain a return period of 50 years, 80-year and 100-year 12-hour maximum dew point and wind speed persistence for long periods, the separation of each month, and the resolution of each decade, through software SMADA and HYFA.

   5: Purvay of Rain maps and DAD chart is also the main stages of this work.

   6: Finally, weather maps, humidity maps and omega air maps at ground level, 700 level and 850 hp prepared from

    Days prior to completion until the day of rain showers in the stormy period from the NCEP / NCAR site and was ready in GRADS software environment.

     In order to realize the adiabatic saturation warmest period of the most intense storms in 1355-1390The maximum instantaneous rate of discharge and daily rainfall statistics, the most comprehensive and stations on their occurrence in the previous chapter, was studied.So the four pervasive  hurricane was  selected. Then, rain storms map were plotted in the GIS software environment and use of IDW method and Using data from the windy days selected on rainfall stations in the study area. In order to obtain the rainfall in the whole region,were regressed  between the two parameters: precipitation and elevation; and was estimated average of rainfall in the cumulative area and rainfall amount in during of the storm days. Based on the height - area tables of ​​each storm separately, DAD curves was drawn based on average rainfall in columns cumulative and cumulative area. Then we reviewed and interpreted weather maps at ground level, elevation Maps, humidity maps and omega maps at 850 hPa level. Survey maps showed Tongue of immigrant anticyclons in North West Europe that usually is deployed on the Black Sea will advection cold air from the above widths on the Caspian sea and is transmited very wet weather to the south and West south Caspian Sea. After analyzing weather maps, the next step is obtain  to water for showers.To calculate the rain water the best way is getting the hottest adiabatic saturation that occurs with the maximize the dew point temperature and wind speed. After obtaining the maximum dew point and wind speed factor, we would like to calculate the coeffcient storm. After obtaining the coefficients of the storm,obtained its P.M.P by multiplying the amount of rainfall for each storm.

     According to the obtained PMP,was adopted rainfall continued for 24 hours with the numbers 276/95. PMP obtained showed that the storm dated 2/10/2001 of 24-hour duration, has been most intense and pervasive from the two other samples.

Amir Hossien Halabian, Fereshteh Hossienalipour Jazi,
Volume 2, Issue 4 (1-2016)

We can identify the flood not only considering circulation pattern in occurring day but also by studying circulation pattern a few days before fresh event. This subject has mutual approach. In one hand, it indicates  that circulation patterns which were before flood event have important role in determining the conditions and moisture content of studied area and playing the fundamental role in few coefficient of region because it determines the previous moisture. On the other hand, it indicates that we should tracking the rain-genesis synoptic systems from source to end place of their activity for studying floods and their meteorology factors which have created them. By this way, we can acquire more comprehensive recognition about the relationship between circulation pattern and floods. In the other words, the identification of synoptic patterns that have created the flood reveals not only the mechanism of their emergence but also is useful for prognosis and encountering with them. The extensive researches have been accomplished about Inundation in the world and Iran, but Iran haven’t much antiquity about synoptic researches. For foreign researches, we can name researchers such as Hireschboeck (1987), Kutiel et al(1996), Komusce and et al (1998), Krichak  and et al (2000), Rohli and et al (2001), Kahana (2002), Teruyuki Kato(2004), Ziv and et al (2005), Carlalima and et al (2009). The numerous researchers have studied the Inundation climatology in internal of country such as Bagheri (1373), Ghayour (1373), Kaviani and Hojatizadeh (1380), Moradi (1380), moradi (1383), Mofidy (1383), Masoodian (1384), Masoodian (1384), Hejazizadeh et al(1386), Parandeh Khozani and Lashkari (1389). In this research, we considered the heavy precipitation of Azar 1391 in southwestern of Iran that resulted in flood phenomenon in the cause and effect manner so that can do necessary prevention actions before occurring the flood for preventing the probable damages and optimal use of precipitations by forecasting the patterns that have created the flood.

In this synoptic study, we need to two database: one group is variables and atmospheric data consisting of geopotential height of 500 hpa level (in meter geopotential), zonal wind and meridional wind (in m/s) and special humidity (in gr/kg) during this times 00:00, 06:00, 12:00 and 18:00 Greenwich in 0-80° northern and 0-120° eastern with local resolution of 2.5*2.5 Arc that have been borrowed from database of (NCEP/NCAR) dependent to National Atmosphere and Oceanography Institute of USA, and other group is daily precipitation data of region rain gauge stations during 4-8th Azar of 1391 (24th November – 28th November 2012). In continuation. By applying the environment- circulation approach, we took action to drawing circulation pattern maps of 500 hpa level, thickness of atmosphere patterns of 500-1000 hpa and moisture flux convergence function from 4-8th Azar of 1391 (that for calendar, conform with 48 hours before beginning the showery precipitation until ending the storm activity) by using data which obtained from database of NCEP/NCAR and the synoptic conditions of above flood have been studied and interpreted in the region.

Flood is one of the most destructive natural hazards that have imposed and impose many damages to people during the history. Hence, the final aim of this research is to explain the key interactions between atmosphere and surface environment and in other words exploration of the relationship between circulation patterns leading to the flood generating precipitation in the southwestern of Iran for forecasting the time and intensity of showers occurrence that lead to flood. For this purpose, by applying environmental-circulation approach, the circulation patterns identified and studied which resulted in flood generating precipitation. The result of this research indicated that torrential precipitations in the region have formed the deep trough in days 4-8 of Azar on the east of Mediterranean and the studied region placed in the east half of this trough that is the location of atmosphere instability. At same time, thickness patterns, indicate the flux of cold air from northern Europe to lower latitudes and spreading the warm air of north of Africa to latitude 50° northern. As a result we expected the frontal discontinuity in the encountering place of these two air mass. Analysis of the moisture flux convergence patterns also indicated that torrential precipitations were the result of moisture flux from Mediterranean and Persian Gulf; and Red Sea and Arab Sea taken into account as reinforced sources.

Tahereh Soltani Gord Faramarzi, Abbas Mofedi, Amir Gandomkar,
Volume 2, Issue 4 (1-2016)

For a synoptic analysis of high polluted days in 13 and 14 November 2007, a combinatorial synoptic analysis was used. From methodology prospect, the present study has utilized the "circular environment" synoptic approach and with respect to the restrictions on very high-polluted days in Mashhad city, the subjective synoptic analysis used for data processing and analyzing the prevailing atmospheric conditions.

In the present research, four sets of the data, including the pollution data recorded at the stations monitoring air pollution, digital atmospheric data, data of upper air stations and the outputs of HYSPLIT model were utilized. The data on air pollution obtained from the Department of Environment Protection of Khorasan Razavi were related to Wahdat station located in the center of Mashhad city. The pollutants include CO, NO2, SO2, ozone, and particulate matter (PM10(  prepared and processed on a daily scale for a 7-year statistical period (2005-2012). When studying the quality of air pollution over Mashhad city, it is necessary to indicate that Mashhad city had only one station monitoring air pollution (Wahdat station) until 2010 and unfortunately, out of 10 present stations for monitoring the air pollution, only Wahdat station was involved a suitable statistical period duration to be studied. Accordingly, the present study has been conducted only by using the pollution data recorded in Wahdat station and utilizing the data of other stations ignored due to the shortness of statistical period duration. The reanalyzed data of the National Centers for Atmospheric Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) with a horizontal separation 2.5 × 2.5 were used in order to study the atmospheric conditions. The atmospheric conditions include the sea level pressure, geo-potential height, vertical velocity, and orbit wind (u) & meridian wind (v) components on different atmospheric levels from the past 48 hours and in a 6-hour interval. In addition, upper air data about Mashhad station (Mashhad airport) were used on a similar period. Upper air data have been obtained from the website of Wyoming university ( on under study days, including air temperature,  dew point, direction, wind intensity and the atmospheric stability and instability conditions (based on Skew-T Curves – logP). These data are only available on Zero Greenwich hour. The outputs of the HYSPLIT model were also used as complementary data for tracing particulate matter in days 10 -15 in November. In this study, the HYSPLIT model, version 4.9 was used. In the present research, the role of regional atmospheric circulation and pressure patterns were investigated on a synoptic scale in very high-polluted days in November 2007 in Mashhad metropolitan. For this purpose, the mechanism dominated on occurring a very high-polluted period in this city was analyzed using a combinatorial method based on synoptic and thermodynamic analyses as well as tracing particulate matter. The results of studies involve the following findings: the days 13 and 14 November 2007 (22 and 23 Aban, 1386) show the highest concentration rates among the polluted days in Mashhad city. The findings of the research show that the synoptic pattern dominated the very high polluted period (13 and 14 November 2007) is a migrant high-pressure pattern. Accordingly, it may be concluded that the incidence of serious pollutions in Mashhad is initially the result of interacting local conditions with air circulation on a regional scale and then the other local factors. In the other words, Mashhad city would experience very high-polluted days only when regional atmospheric circulation provides suitable conditions to increase the concentration of pollutants. What is obvious is that in the winter season the serious pollutions occurred in Mashhad city are mainly as the results of prevailing extra-tropical systems (migrant anticyclone). Studying subjective synoptic analysis, tracing the backtracking of particulate matter and the atmospheric thermodynamic conditions ( combinatorial synoptic analysis) have provided a deeper and more accurate understanding of the conditions prevailing in the occurrence of serious pollutions in the northeast of Iran. Studying the output of the HYSPLIT model indicates that the migrant stack system of western wave together with the subtropical stack would control the air circulation pattern on the northeast of Iran in 13 and 14 November 2007. Tracing the particulates shows an anticyclone system on the zone. Also, studying SKEW-T Curves related to the migrant high-pressure pattern revealed a different structure, so that the day 12 November 2007 faced with a radiation inversion along with an increased temperature, but on day 13 November 2007 an inversion from the sort of subsidence between the interval of level 850 to 700 hpa was appeared and also reached to higher than 700 hpa.

Saeed Balyani , Mohammad Saligheh,
Volume 3, Issue 2 (5-2016)

The results of this study indicated that the synoptic patterns that lead to heavy rainfall in 22 March 1996, 24 mar 1995 and 17 November 1994 in the northern portion of FARS province includes: the low pressure that located in eastern part of Mediterranean and Black sea and southern part of Caspian Sea that created by trough that located at the middle level of atmosphere. In addition to this low pressure, the bipolar pattern in of Saudi Arabia  having negative vorticity that lead to transporting moisture from (India ocean, Red sea, Arab sea, Persian gulf and Oman Sea )   and also to be alignment with east Mediterranean sea and black sea low pressure as ascending agent lead to precipitate of rainfall in mentioned days . and also we found that in 29feb 1996 as second patterns rainy day, a strong deep trough transporting moisture from Soudan region and east Mediterranean  low pressure, cause alignment of this atmospheric systems. In fifth patterns (21 mar 2001), existing an low pressure and positive vorticity center in east of Pakistan simultaneously with existing negative vorticity center in central part of Iran, lead to high pressure gradient which cause rainfall events in study area. The main founding of this study were that reveals the role of low pressure of east, north and south of Caspean sea in heavy rainfall events in study area.

Pre-warning of natural hazards events such as heavy rainfall has a significant effect in damage reducing. The analysis of synoptic-dynamic condition of atmospheric circulation patterns, has great importance in recognize affective agents in heavy rainfall events. Especially this heavy rainfall could lead to flash floods suddenly. This study's aim is to analysis and extraction of daily heavy Rainfall lead atmospheric patterns in northern portion of Persian gulf (Helle and Mond Subbasin).

The study area, Helle and Mond basins, with about 21,274, 47653 km2 area,respectively are located in the south of Iran. The Helle basin approximately is between 28° 20'N and 30° 10'N latitudes and between 50° E and 52° 20'E longitudes and Mond basin is between 27° 20' and 29° 55' latitudes and between 51° 15' and 30° 27'E longitudes.These basins are located in sides of a massive sources of moisture, Persian Gulf.

In this study we investigate the data of daily rainfall of 37 synoptic and meteorological station of study area during 1991 to 2011(20 years) to extraction the atmospheric patterns lead top heavy rainfall. In this study in order to archiving heavy rainfall days based on 95 percentile in study area, the data of sea level pressure, geopotantial high of 300 and 500 hp and also data of verticit and stream line and omega in the spatial framework of -10 to 100 longitude and 10 to 70 Latitude has been selected. Then we create the sea level pressure matrix as rainfall associated days, based on Lond method of Correlation to classify days.

Our founding indicated that the main synoptic systems that lead to heavy rainfall is related to low pressure in eastern Mediterranean  and southern part of Caspian sea. So that in detected rainfalls patterns shown that the transporting moisture from nearby sea by high pressure of Saudi Arabia by associating eastern Mediterranean low pressure and deep strong trough in east and southern part of Caspian sea  cause heavy rainfall events in study area. So that the low pressure located in eastern and southern portion of Caspian sea could affect the study area.

Alireza Hosseini, Hediyeh Akbari Ghamsari,
Volume 3, Issue 4 (1-2017)

Classifying daily climate circulation patterns has always been considered by climatologists. Investigating climate changes such as rainfall and the temperature in a same single time and place suggests that these changes are strongly influenced by atmospheric circulation patterns.

Regarding so, climate changes, known as variables here, such as rainfall, temperature, and other related phenomena, which are exemplified as flood, drought, glacial, and etc. are associated with special types of climate circulation patterns. The continuity and alternation of the systems are classified or identified climatically, therefore weather classification system is one of the main objectives of the synoptic climatology (Huth, 1996). Since every weather type creates its own special environmental condition, lack of identification in weather type frequencies leads to a difficult environmental explanation and alternation (Alijani, 1380: 64).

Identifying atmospheric circulation patterns different things that can be expressed inductively such as frequency, intensity, and spatial distribution of climate changes in rainfall and its physical causers (VicenteSerrano and LopezMoreno, 2006).

Heavy rainfall in many watersheds, particularly in the basin and sub-basin which involve less time exposure, causes floods and it also damages human, natural resources, infrastructure utilities and equipment. Before the occurrence of this kind of rainfall, it requires a deep understanding of the synoptic systems of their creator. This understanding is only possible through the classification and identification of rainfall patterns which used to cause floods in the studied basins.

The present study also aims at identifying and classifying the synoptic patterns of rainfall during the statistical stage of the study in the basin which caused flood in Taleqhan basin.

Taleqhan basin with area of (65/1242) per square kilometers is located in "36֯, 5', 20" to "36֯, 21', 30" north latitude and "50֯, 36', 26" to eastern longitude "51֯, 10', 18".

The study area is 120 kilometers away from North West of Tehran and located in a relatively high mountainous area in Alborz Mountain. This area is ranging from 1700 meters to 4400 meters above sea level. Average rainfall in this basin ara is 515/16 mm and its annual temperature fits 10.5 centigrade.  About 79 percent of rainfalls occurs from the cold weather period in November to March. It is also know as semi-humid cold weather based on the De Martonne classification.

Circulation algorithm (CA) and pattern clustering algorithm (PCA) were determined based on the daily methods in synoptic scale by applying information from stations in Taleqhan basin (Gateh deh, Dehdar, Dizan, Snkranchal, armouth, Ange, Joostan, Zidasht). In order to classify the weather type, daily average rate of 500 HPa and the sea level pressure (SLP) were extracted and reconstructed over the period (1980-2011) at the 2.5 degree of NCEP. Selected range includes 608 points from latitude of 10 to the 60 of northern degree, and latitude of 10 to 80 of eastern degree.

Principal components method mixes the interrelated points and reduces the matrix size, so 13 main components are remained that they includes 93 percent of the total variance. This study employs S array and Varimax rotation to identify different types of weather. It also makes use of K-Means clustering method to classify daily weather types. And finally, a matrix was formed in 118×608 dimension for 118 common days of rainfall among stations. All days were divided into four groups. They offer the most common climate circulation patterns in the proposed area. At the end, and finally integrated maps of sea level pressure and 500 HPa were drawn for each weather type. 

According to the results from factor analysis, 13 main elements were selected that they included 93% of the total variance of the data. According to the above mentioned method, all days (118 days) during the statistical period (1980-2011) were divided into 4 groups which provide the most climate circulation patterns in the study area. Then, integrated maps of sea level pressure and 500 HPa range were drawn for each of the types. Clusters were numbered according to the K-Means arrangement, and they were named based on the pressure patterns and the way circulation lines were ordered.

The classification shows two different resources for rainfall in this basin.

A: Those rain systems that are entered to the country from the West and South affect this basin. These systems humidity are caused by the Red Sea, the Mediterranean sea, the Black Sea, and the Atlantic Ocean. (B) Some parts of the Caspian coast rainfalls and the northern part of the Alborz mountain that has received their humidity from the Caspian Sea and it has infiltrated northern high-land, causes the rainfalls. It enters the basin from the wide valley of Sefid Rood. According to the rainfall measuring stations data, the least rainfall area is in western, which includes low-land areas. And the most rainfall area is its northern east. Rainfall in this area, in terms of rainfall time distribution in a year, is the Mediterranean. It does not involve a complete dry climate in summer and it takes 3 to 4 percent of the total rainfall.  Rainfall in the basin, respectively, is distributed in winter, spring, fall, and summer.

Elham Ghasemifar, Somayeh Naserpour, Lyli Arezomandi,
Volume 4, Issue 2 (7-2017)

Precipitation is not only a critical process in global hydrologic cycle but also an important indicator of climate change (Fu et al.,2016). Precipitation is a key factor of the global water cycle and affects all aspects of human life. Because of its great importance and its high spatial and temporal variability (Thies and Bendix.,2011). Climate change is caused many extreme climatic occurrences in recent decades. One of most   important   extreme   events   is   extreme   precipitation. The changes of temporal-spatial patterns of precipitation may potentially cause severe droughts or flood hazards (Jiang et al., 2008).  There   are   many environmental damages which are related to these events. Precipitation events were examined and studied by many researchers. The purpose of the study is evaluating of the structure and origin of the events in the west of Iran. Studies    about   extereme   precipitation   is   somewhat   strong.     Robert,   1993 evaluated many flashflood in United States which is related to short wave at 500 hgt   level.   Many   researchers   also   studied   this   type   of   precipitation   such   as Kumar, 2008 and etc. Trend analysis is another approach is related to this scope. Globally, precipitation increases in equatorial rain bands; decreases in subtropics as greater tropical convection in the rising branch of the Hadley circulation will lead to enhanced subsidence in the subtropics; and increases in high-latitudes due to increase in moisture transport (Huang et al., 2013). Synoptic analysis of the events is required due to increseing trend of this events and tremendous socioeconomic impacts on many places. First,   a   99  percentile   for recognition of  extereme   precipitation  is applied  for  daily precipitation during 2000-2015 at seven weather stations in the west of Iran. Then principal component analysis carried out in order to reduce correlated data (SLP, hgt at 500and 850level) which is associated to synoptic patterns. Two extereme   precipitations are   selected   for   synoptic   analyses.   In   order   to   better   perspective   of   these patterns   analyses are performed using sea level pressure, 500 and 800 hgt level,   omega,   u-wind,   V-wind,   relative   humidity,   and   TRMM   precipitation Radar data. TRMM data is used due to satellite systems provide a unique opportunity to monitor Earth-atmosphere system processes and parameters continuously and the correct spatio-temporal detection and quantification of precipitation has been one of the main goals of meteorological satellite missions (Thies and Bendix.,2011).
The results of precipitation data showed extereme   precipitation dates based on 99 percentile are as fallows during 2000-2015 time period: 29 Jan   2013,   30 Nov   2008   ,   3   and   4   feb   2006,   25 Dec 2004,   13   jan 2004, 1 dec 2001, 24 mar 2000, 2 may 2010, 29 and 30 Oct 2015. After identitying extereme   precipitations, PCA (principal component analysis) applied for SLP data, Geopotential hight at 500 and 850 levels data in oredr to  recognition the synoptic patterns.   The   results   indicate   that   there is only   one   component   which   explains   99 percent of variances of data. Therefore the one synoptic pattern incorporated in formation of  extereme   precipitation in the west of Iran. Then for better understanding of this pattern, we are selected two extereme   precipitation reanalysis data  (29 oct 2015) and (13 Jan 2004)  and evaluated sea   level   pressure,   500  and  800   hgt   level,  omega,  u-wind,  V-wind,   relative humidity,  and   TRMM   precipitation   Radar   data in   these   dates. The purpose of this proccess was monitoring different parameter in two dates.  The results illustrated interesting conditions which is related only to providing appropraite condition for extereme   precipitation formation. Many   conditions required to the events as fallows: SLP lower than 1000 hpa over the west of Iran, surface relative humidity larger than 70 percent, negative omega lower than -0.3, positive vortices which indicate cyclogenesis. Another most important factor which caused extereme   precipitation is location of trough. In all cases, the western of Iran located in front of trough at 500 and 850 hpa. The Precipitation Radar   of   TRMM  satellite   also   determined   same   precipitation   patterns   which are specific for the west of Iran.   This is only one part of the heavy precipitation  studies at west of Iran the authours sugesst climate change studies such as trend analysis in a long time period, simulation with regional models as Regcm and WRF,  appling ERA-interim data which can provide fine spatial resolution up to 0.25 degree over study area which  need to be done in order to completion of the results.

Faryad Shayesteh, , ,
Volume 5, Issue 1 (6-2018)

The role of tropospheric vertical anomalies in rainfall solid Case study: the hazard of hail in Kermanshah
Climate risks is one of the Types of hazards that damages human communities such as the phenomenon of hail, in the micro-scale, it causes financial losses and casualties. Hail is associated to the atmospheric elements and geo-location factors. Whenever weather conditions and appropriate physical processes are combined with geo-location creates and intensifies this phenomenon.
Losses resulted from hail has been more effective in the agricultural sector and in the effect of damaging the crops When growth and budding. However, it disorders in other sectors such as, blemishing residential buildings, Losing large and small animals also, damaging to the aircraft flight and its components. Hail considerable damage in Kermanshah province every year so that Farmers insure their crops against this Phenomenon and the government will incur heavy costs for
damage that is inflicted on the sector of activity.
Research methodology
The current weather data has been used with 3-hour intervals in the statistical period of 65 years (1951 to 2016) from synoptic stations of Kermanshah Province that includes the stations of Kermanshah, West Islamabad, Ravansar, Kangavar, West Gilan, and Sar-e-Pole-Zahab.
Among the 100 present weather code, Codes 99, 96, 91, 90, 89, 87 and 27 have been considered that including hail phenomenon by varying intensities and includes any appearance of this phenomenon in Hours scout and three hours earlier. Then, based on the above code, Were coded in Excel to identifies Codes 96, 91, 90, 89, 87 and 27 When entering from the Meteorological Data To the desired program among Group VII of the data, And when the written code, were identified, Hail days were marked.
Given that in this study Hail is studied regarding the synoptic conditions and temperature anomalies. Therefore, for the synoptic situation, Pressure data, vorticity, Special moisture, Components U and V, Omega transverse profile And outgoing longwave radiation, And for the temperature anomaly, Temperature and isothermal anomalies components Were getting from site And using the software Grads were drawn maps for a selected day To determine the formation of hail.
Commentaries Results
The frequency of occurrence of hail has reached 187 in the period 65 years in Kermanshah province. This phenomenon generally occurs from mid-September to mid-June. The most number has been in Kermanshah station and the Least in Sar-Pol-Zahab station.
April has had the highest number of hail frequencies in Kermanshah province and the greatest losses in the month related to the agricultural sector. Therefore, Select System hail seems essential to examine how the temperature anomalies and the formation of hail in the month.
On the day of the event, trough hail has been formed in the East Mediterranean.Wrying the trough axis From North East to South West resulted in cold air from high latitudes to the East of the Mediterranean.
The establishment of trough in the middle and low pressure level in sea level and its following Convergence in the balance has created positive omega until balance of 200 hPa and most serious it is at the level of 400 hPa. Negative omega has maintained its association from ground surface until High levels in the study area.
The airflow of vorticity balance 1000 and 500 Hpa Suggests vorticity positive settlement area on the case study. Establishment of short wave in the vicinity of the study area and intensifying ascending conditions also Prolong Positive trough conditions from surface of Earth until 500hpa balance have been The necessary dynamic conditions for Hail in this day.
Special moisture and wind Vector with 700hpa balance of Moisture transfer has been done by two opposite vorticity system. Trough rotary motion Based on the Mediterranean and along the Red Sea on the one hand and Moving anticyclone over the Arabian Sea And the Persian Gulf and Oman Sea on the other, have conveyed Moisture of all moisture sources from The seas around to The study area.
Also OLR anomalies for the hail event day indicates being Negative in the study area and the sharp decline of Outgoing longwave in this day Compared to its long-term average And hence the conditions of cloudiness and the formation and intensification of convection has been provided.
1000 hpa positive anomaly 2 ° is representative the Higher than the average temperature conditions and in the 500hpa anomaly balance Minus 2 degrees Celsius is representative Lower than normal temperatures in the balance. These factors aggravate the vertical temperature gradient in the study area these days. 20+ degrees Celsius the Isothermal curve and -20 ° C. Respectively, the levels of 1000 and 500 Drawn to the area of study And has created a large temperature difference Between the upper and lower levels.
Keywords: Synoptic analysis, Hail hazard, Tropospheric anomalies, Vorticity, Kermanshah Province

Ma Mahmoud Ahmadi, Fj Farzane Jafari,
Volume 5, Issue 3 (12-2018)

Problem statement
The occurrence of terrible floods due to climate change has caused much damages in different parts of the world in recent decades, and the effect of these changes is more pronounced in dry areas. Floods are the most common environmental damage. On average, 60 floods occur annually in Iran, with an average annual flood loss of 141 people, meaning more than 2 deaths per year per flood event.
Research Methodology
The study area consists of six stations located in Hormozgan, Kerman, Yazd, Kohgiluyeh, and Fars provinces. In this study, two types of ground and high data are used as follows:
A) - Using daily rainfall data of the 44 years (1967-2014) statistical stations of the region obtained from the country's Meteorological Organization
B) Use of high-level data. Includes revised data for geopotential heights, sea level pressure, wind direction, meridian wind, omega, and humidity, from the National Center for Environmental Excellence at Colorado. To conduct synoptic analysis, the circular environmental method was used; after observing the daily rainfall during the statistical period of all rainfall over 50 mm in selected stations of Yazd, Jiroft, Shiraz, Bandar Abbas, and Yasuj, 118 heavy rainfall events were investigated. After identifying and separating days, 105 observation systems were identified and analyzed.
After the evaluation and control of the pressure maps of the sea of the systems of landing, 4 patterns were selected and identified.
Explain and interpret the results
The results showed that heavy precipitation occurred in the months of December, December, February, February, and November, respectively. Since November, with the retreat of high-performance dynamic systems to the southern latitudes and the influx of western winds from high latitudes on the area, conditions for the occurrence of heavy rainfall are provided. Most centers with 9 heavy rainwater systems of Sudan's lowland, 6 the moderate Sudanese-Mediterranean component of the Middle East has been on Iraq, and the four satellite systems have been the Mediterranean-Sudan-Mediterranean integration. The most frequent Sudanese pattern in 2-day continuity with 17 cases was Sudan-Mediterranean integration pattern with 7 cases in 3-day continuation, Sudanese-Mediterranean integration pattern in the Eastern Mediterranean, 4-day continuity with 7 events, and equidistant Mediterranean pattern The continuity of 2 to 4 days has been due to the increased load of Mediterranean systems ranging from 70 to 90 mm.
Mr Dana Rostami, Dr Seyed Asaad Hosseini,
Volume 5, Issue 3 (12-2018)

 Dust is one of the environmental hazards and atmospheric phenomena familiar to residents of the southern and southeastern parts of the country. Which each year causes a lot of damages to various sectors such as environment, agriculture, health, transportation, facilities, and so on. Therefore, in this research, we investigated and identified the sources of dust in the area, the intensity and frequency of dust, its governing patterns and dust-free areas during the 30-year statistical period (1984-1984). The research method is a combination of statistical, synoptic and remote sensing analysis. The data used include the hourly data of 22 synoptic stations (8 times per 24 hours), CDC1 data up to 2006, and then GDAS data, temperature, wind direction and wind speed, geopotential height at different levels. In selecting the studied days, it was tried to select the selected samples with a duration of three days and more, the spatial expansion of at least 4 stations with horizontal vision less than 1000 meters. For this purpose, were used the characteristics of the 11.3 and 12-micrometric wavelengths of the wavelengths were used to visualize the dust on the MODIS images from the ENVI 5.2 software environment, to track the wind direction from the GDAS data in the HYSPLIT software environment and to study the maps of various atmospheric levels from Temperature, wind speed, wind speed and geopotential heights were used from GRADS software and weather data stations. The annual frequency of the occurrence of days with dusty phenomena in the study area showed that during the statistical period of 1984-2013, a total of 11616 days with dust was recorded with the 06 code for south and southeast of Iran at the stations study. Most days with the dust event at Zabol Station with 1136 days and the lowest occurrence occurred at Bandar Abbas Station with 171 days during the studied period. In general, the annual survey of the data shows that the phenomenon of dust in the stations study in the past has been high and very high; however, in recent years, it has been expanding more and more than the past, and has been growing. The results of the monthly and seasonal surveys showed that the summer and the months of June, July, August and May are the most frequent and most frequent, with a peak of 1000 meters, respectively, and December have the lowest dust incidence and Zabul and Zahedan station

Zahra Hejazizadeh, Meysam Toulabi Nejad, Zahra Zarei Chaghabalaki, Behzad Amraeei,
Volume 5, Issue 4 (3-2019)

This research was conducted to identify the dust storms in the Midwest of Iran from June 16 to 19, 2015. To investigate the synoptic conditions of the causes of this phenomenon, the ECMWF has an array of 0.125 degrees, including geopotential, omega, and sea level pressure, orbital and meridian components of the wind, specific humidity Soil moisture was applied to a depth of 10 cm. Similarly, for the purpose of routing the source of dust particles, the model of the Minimum Meteorological Parameters (HYSPLIT) Marv was used. The results of this study showed that in Lorestan province, non-ditches created by low-pressure thermal springs and high-altitude movements in Saudi Arabia caused the convergence and sucking of flows to the west of the country, as well as the establishment of a low-pressure cut at the middle levels of the atmosphere in the east of the Caspian. In the event of this risk, it has been effective. According to the average soil moisture from the surface of the earth to a depth of 10 cm in days with dust hazards, the moisture content of dust particles in the dust was less than 15%, due to the flow of streams from these fields without sufficient moisture, fine particles the soil is easily directed towards the study. A survey of Hysplit tracking maps shows that two general paths for the transfer of dust to the studied region can be detected. 1-Northwest - Southwest At an altitude of 1500 meters: passing through the dust nuclei formed in the northwest of Iraq and east of Syria, carry out the transfer of dust to the west-west of Iran. As these currents have been able to transfer dust to the southwest of Iran, this path can be considered the main route of dust dispersion to the region. 2- The western-eastern route at an altitude of 500 to 1000 meters: is the source of particles of this route inside the country (around Hurralazim) that entered the West of Iran and greatly reduced the horizontal visibility, which is the main source of dust on June 18 and 19. The investigation of the path of dust particles in the walnut shows that these particles were initially transferred to lower levels by low-pressure systems in the Midwest of Iran and then pulled in three directions on the ground.

Mr Ali Hasanzadeh, Mr Hooshmand Ataei, Mr Nader Parvin, Mr Amir Gandomkar,
Volume 6, Issue 1 (5-2019)

Agricultural crops have damaged a lot due to the aftermath of late spring frost, and because low temperatures have damaging effects on agricultural production, it is essential to anticipate and prevent potential damages. Often, atmospheric temperature variations are very urgent due to the high temperature of the systems and the plants cannot adapt themselves with severe oscillations and, have been damaged. The aim of this study was to analyze the climate of the spring frost in Kermanshah, identifying the sea level equations and the late spring freezing frost of the period from 1990 to 2015. This survey has been done to determine the period of the freezing phenomenon, determine the minimum daily temperature of 7 stations placed in Kermanshah,  Hamedan, and Ilam. After analyzing the data of spring frost freezing of Kermanshah province using the main component analysis technique and hierarchical clustering method, the most common 10 patterns of late spring coldness of the area were studied and determined. In 10 resulting cluster, 8 clusters were related to the high-pressure pattern of Siberia. From the total 91 days of spring frost freezing in Kermanshah province (79% (72 days)) is due to the high rainfall of Siberia, 12% (11 days)  is due to the Mediterranean climate and 9% (8 days) is due to the Van lake climate. These pressure patterns were named according to the location of their deposition, which caused the loss of the environment and the freezing frost of the spring.
Yousef Ghavidel, Manouchehr Farajzadeh, Bashir Ghahramani,
Volume 6, Issue 2 (9-2019)

The application of Extreme value analysis method in heat wave hazard climatology; case study in Mid-Southern Iran
Greenhouse warming poses the main cause of atmospheric hazards’ exacerbation and emergence in recent years. Earth planet has been witnessing frequent and severe natural hazards from the distant past; however, global warming has strongly influenced the occurrence of some atmospheric hazards, especially the ones induced by temperature and has increased the frequency and severity of those risks. Such extreme risks arising from temperature element and being affected by global warming could be referred to hot days and their frequency more than one day which undergo heat waves. Of the studies conducted worldwide in conjunction with the phenomenon of heat waves, the following can be pointed out; Schär (2015) has focused his studies on the Persian Gulf and the worst heat waves expected in this area. The recent work revealed an upper limit of stability which enables the adaptability of human body with heat stress and humidity. If people are exposed to a combination of temperature and humidity over long periods higher than this level, they will lead to hyperthermia and death, because heat dissipation from the body is physically impossible. Paul and al-Tahrir (2015) using a high-resolution regional climate model demonstrated that such a situation can occur much earlier. In Iran, in relation to heat waves, Ghavidel (2013) analyzed climatic risk of Khuzestan province in 2000 regarding super heat waves using the clustering approach. The obtained results unveiled the establishment of a low pressure at ground level and high pressure dominance at mid-altitudes up to 500 hp as well as the increase in atmosphere thickness having led to the ground overheating. Added to that, the source of heat entering into Khuzestan is advective and hot and dry air transport through Arabian Peninsula, Iraq and Africa. Ghavidel and Rezai (2014) addressed in a study to determine the temperature-related threshold and analyze the synoptic patterns of super heat temperatures in southeast region of Iran; the results of study approved that the only pattern effective on the occurrence of super heat days in Iran’s southeast is the establishment of the Grange’s heat low-pressure at ground level and subtropical Azores high elevation dominance at 500 hPa level. In this study, absolute statistical indicators, also recognized as above-threshold values approach, were used in order to identify, classify and heat waves synoptic analysis in the warm period of the year in the southern half of Iran. To use above-mentioned indicators, firstly daily maximum temperature statistics of studied stations with the highest periods were averaged every day once in June to September and once for the months of July and September. Using statistical indicators of long-term mean and standard deviation or base period, indicators would be defined for the classification of heat waves and days with peak extreme temperatures. In such classifications, usually long-term average or base period is multiplied by 1 to 3 to 4 times standard deviation and each time is account for the factor of each class.
To select the days for synoptic analysis, averaging was performed of all classified waves into four heat wave categories of low, intermediate, strong and super heat; accordingly based on the maximum blocks in each class of heat waves, days that had the highest temperature values were selected as the class representative for mapping and synoptic analysis.
This study dealt with investigating heat waves synoptic during the year’s warm period in the southern half of Iran. Studies showed that a variety of synoptic systems in the year’s warm period affect the study area. As well as, synoptic analyses concluded that in the southern half of Iran over the year’s warm period when occurring heat waves, low-pressure status dominates the ground level (caused by Gang’s low-pressure and local radiant mode); thus high-pressure status with closed curves is prevailing in atmosphere’s upper levels that gives rise to the divergence, air fall and Earth's surface heating. Studying the status of the atmosphere thickness in the days with the heat wave in the study area indicates its high altitude and thickness that this itself implies the existence of very hot air and susceptibility of the conditions for the occurrence of heat waves. In addition, wind maps at atmosphere’s different levels well illustrate the wind of very warm and hot air masses from the surrounding areas to the southern part of Iran; therefore it can be noted that aforementioned hot air masses mainly wind from places like different regions of the Arabian Peninsula, Iraq, North Africa and the low latitudes to the study area.
Keywords: Synoptic analysis, heat waves, maximum blocks, southern half of Iran.

Dr. Aliakbar Shamsipour, Mr. Ayoub Jafari, Mr. Hesam Bostanchi,
Volume 7, Issue 2 (8-2020)

Occurrence conditions for severe snow blizzard in the west-north of Iran
The blizzard incident is one of the climatic hazards that occurs due to the combination of other climatic factors such as temperature (below zero), snow and wind (at 15 m/s). In this research, the conditions of blizzard in Northwest of Iran are carried out using statistical methods. By analyzing all the meteorological codes of the blizzard (36, 37, 38 and 39) during the statistical period from 1987 to 2016 for 11 synoptic stations of the study area, codes with severe blizzard (37, 39) were selected. Then, using the geopotential height, wind and Leveling temperature of 500 and 850 hpa, obtained from the NCEP/NCAR open source database, the synoptic patterns of blizzard incident analyzed. Statistical analysis of the relationship between the effects of geographic factors on severe blizzard has shown that the factor of height has the greatest effect on intensity, increase and incident spatial differences of this phenomenon. The study of the synoptic patterns of the incident of the blizzard phenomenon showed that five main patterns play a role in creating it in the region. The synoptic patterns of development include the formation of a low cut-off center, a long landing passage from Iran, the formation of a relatively deep and drawn Mediterranean East, The rectangular system is a rex-shaped system and is an umbilical bundle system. Among the patterns obtained, the patterns that were bundled were, the most important role in the survival and transfer of flows associated with cold, and other patterns, despite the frequency they had, were periodically of severity and weakness.
Keywords: Blizzard; North West; Wind speed; Temperatures below zero; Synoptic patterns
Human life is always affected by climatic phenomena, especially the hazards of the two variables of temperature and wind. One of the most important simultaneous phenomena of these two variables is the blizzard, which is caused by heavy snow, stormy winds, and very low temperatures. This climate risk can cause damage to various areas of horticulture, agriculture, urbanization, transportation, and so on. This phenomenon is present in regions such as Canada and North America with a cold weather wave that results from turbulence in the winters and damages the lawns in these areas. There are plenty of local storm in the polar regions and it lasts for a few days. For example, the wind in the Adelie land in the Antarctic is so severe that the area is known as the storm Land. In Iran, the most significant blizzard occurred in mid-February 1350, resulting in the deaths of more than 4,000 people across the country. In this research, considering the characteristics of the blizzard phenomenon at the time of occurrence (severity, continuity, expansion, and time of occurrence), the study has been conducted to determine the statistical synoptic patterns in the northwest region.
In this research, the studied area is northwest of Iran, which includes 6 provinces (Ardebil, West Azarbaijan, East Azarbaijan, Zanjan, Kurdistan, Kermanshah, Hamedan). In order to study, the days with the blizzard phenomenon in the form of 3 hours and in codes of this phenomenon (36, 37, 38 and 39), were obtained from the establishment of the stations studied by 2016. In the following, for precise examination, stations with 30 years of statistic from 1987 to 2016 were identified and the statistical (frequency, daily, monthly and annual frequency) codes 39 and 37 were studied. Finally, the relationship between blizzard with the latitude and elevation in the studied stations was determined. To assess the statistical results, the correlation coefficients (R) and coefficient of determination (R2) were used.
In the second part, the identification of synoptic patterns was done by Principal Component Analysis in MATLAB software and ocular method. The criterion for identifying synoptic patterns, the days where codes 37 and 39 are more than 1 time (3 hours) within 24 hours or two days behind each other at the stations studied. In order to determine the patterns, at first, the average geopotential data of the 500-hpa level from 1987 to 2016 were obtained from a range of 10-70 degrees north latitude and 0-80 degrees east longitude with a spatial resolution of 2.5 * 2.5 from the NCEP / NCAR data.
Statistical analyzes on the relationship between the effect of geographic factors on severe blizzard showed that the factor of height had the greatest effect on the intensity, magnitude and spatial differences of this phenomenon. In sum, the most important factor in the occurrence of this phenomenon is due to atmospheric conditions and synoptic patterns of the region. In this study, the most frequent occurrence of codes 37 and 39 in all stations studied was at Sardasht station and Khalkhal station, respectively. Also, the statistical study of the frequency of the annual and monthly occurrence of each code showed that code 39 in 1990 and code 37 in the years 1989 and 1990, as well as in January, had the highest frequency of each of the two codes.
Investigating the patterns of the occurrence of the blizzard phenomenon showed that five main patterns have contributed to its creation in the region, the first pattern due to the formation of a low cut-off center, which, with the cold weather in Central and Eastern Europe, has reduced the temperature in the northwest. The second pattern is due to the high landing passage from Iran, which has crossed the descent from a cold and cold weather zone from Europe to Iran. The third pattern is the location of the studied area in the relatively moderate, dragged, eastern Mediterranean wavelength, causing cold weather to fall to the northwest. The fourth pattern, with the formation of a Rex-type blockade on the Mediterranean, has led to the transfer of cold air from Eastern Europe, Kazakhstan, and high latitudes to Iran. The fifth pattern, with the formation of a blockade, has caused cold weather in northern Europe and Central Asia to enter the country from the north, causing a drop in temperature in the region.
Among the known patterns, the patterns that were blocked (pattern 4 and 5) played the most important role in the survival and transfer of cold fluxes and even drawn to lower latitudes. Other patterns, despite frequent periods, provide conditions for the occurrence of this phenomenon and, unlike the blocking patterns, have had severity and weakness.
Keywords: Blizzard; North West; Wind speed; Temperatures below zero; Synoptic patterns
Dr Hassan Lashkari, Miss Neda Esfandiari,
Volume 7, Issue 2 (8-2020)

Identification and synoptic analysis of the highest precipitation linked to ARs in Iran
        Atmospheric rivers (ARs) are long-narrow, concentrated structures of water vapour flux associated with extreme rainfall and floods. Accordingly, the arid and semi-arid regions are more vulnerable to this phenomenon. Therefore, this study identifies and introduces the highest precipitation occurred during the presence of ARs from November to April (2007-2018). The study also attempted to demonstrate the importance of ARs in extreme precipitation, influenced areas and identifies the effective synoptic factors. To this end, integrated water vapour transport data were used to identify ARs, and documented thresholds applied. AR event dates were investigated by their daily precipitation, and eventually, ten of the highest precipitation events (equivalent to the 95th percentile of maximum precipitation) associated with ARs were introduced and analyzed. The results showed that most ARs associated with extreme precipitation directly or indirectly originated from the southern warm seas. So the Red Sea, the Gulf of Aden and the Horn of Africa were the major source of ARs at the time of maximum IVT occurred. Synoptically, seven AR events formed from the low-pressure Sudanese system and three events from integration systems. The subtropical jet was the dominant dynamic of the upper troposphere, which helped to develop and constant of ARs. Moreover, the predominant structure of jets had a meridional tendency in Sudanese systems, while it was a zonal orientation in integration systems. The intense convective flows have caused extreme precipitation due to the dominance of strong upstream flow besides having the highest moisture flux. The station had the highest precipitation has been located in the eastern and northwestern region of the negative omega field or upstream flows.
        Keywords: Identification and synoptic analysis, highest precipitation, Ars, Iran.

Alireza Pilpayeh, Davoud Najafian Ghojehbiglou, Tofigh Saadi, Akbar Rahmati,
Volume 7, Issue 3 (11-2020)

Drought is one of the natural disasters occurring over a long period of time compared to other natural phenomena which intermittently impedes human societies through the negative impacts on water and agricultural resources and subsequently the economy. One of the methods of drought monitoring is the use of drought indices such as SPI. In this study, SPI index was used to study drought over the period 2001 to 2016. The SPI index is purely based on precipitation, so it is important to select a proper precipitation source to extract the SPI index at different time scales. Synoptic stations, due to lack of proper distribution and high statistical gaps, cannot be a reliable source of precipitation in this type of research, so global precipitation datasets having high spatial and temporal resolution can be used as a viable alternative to ground stations, in this study the Era-interim precipitation product, which is the product of the European Center for Medium range Weather Forecast was used. Initial results indicated that the Era-interim precipitation product could be used as a viable alternative to synoptic stations nationwide. Therefore, this precipitation product was used to assess the drought situation in the country. The study of drought status with respect to SPI indicated that with increasing SPI time scale dry and wet conditions became more severe so that mild dry and wet conditions in most in most month and years turned into severe dry and wet conditions.

Kamal Omidvar, Mehdi Mahmodabadi, Parisa Shams, Mahbobeh Amiri Esfandegheh,
Volume 7, Issue 3 (11-2020)

Due to the fact that the mechanism of anticyclone Movements is the desire to descend and suppress the air, so the effect of these movements and their location in the occurrence of flood falls is significant. For this purpose, in this paper, flood precipitation in the last two decades of Kerman province was studied and two of the most severe ones were selected. Due to the emphasis of this paper on the province of Kerman, the heavy rainfall was calculated for each station in the province using the Gumble Type 1 Distribution Statistical Index. Then, the thermodynamic properties of the precipitation were analyzed using radial data and Kerman station's sketch diagram. For analysis of these floods, daily rainfall data of the synoptic station 10 of the province and sea surface pressure maps and850,500,300 hectopascal levels were used. Then, the arrangement of the simulated pattern and its trend in the air maps, were studied during a selective period daily3. The results of the study indicate that the main cause of flood precipitation in the study area is to strengthen the eastern Mediterranean landfall in the middle troposphere, so when moved downward to the bottom of the polar system, it is transmitted to lower latitudes As a result, Western systems, with their movements on the southern warm waters, have a high moisture content and cause heavy rainfall in the region. Also noteworthy in the occurrence of precipitation is the presence of intense swinging movements on the southern waters, especially the Oman Sea, which causes more humidity to be injected into the interior areas of the country and provides the conditions necessary for the occurrence of such rainfall.

Ghasem Keikhosravi, Shahriar Khaledy, Ameneh Yahyavi,
Volume 7, Issue 3 (11-2020)

This study was conducted to investigate the foehn mechanism in the Alborz Mountains.For this purpose, daily temperature, mean and maximum daily temperature, minimum, mean and maximum daily relative humidity, hourly wind direction and velocity data were collected and prepared at 8 selected stations over a 10-year statistical period (2006-2010). To derive the sum of frequency of occurrence of foehn, hot days are extracted using Baldy index and taking into account wind direction relative to station position and temperature rise compared to previous days were identified as days associated with foehn. Then, using NCEP / NCAR database data, different atmospheric alignment maps were obtained for the selected samples and plotted in Grads software environment. Then the position of high pressure cores and adjacent low pressures on the maps were determined. Results showed that Masouleh station with 41 days frequency and Astara and Bandar Anzali station with 18 days had the highest and lowest occurrence of foehn. Investigations on the synoptic maps of 35 foehn events showed that a total of three groups of Anti-cyclone or high-pressure centers were affected by the synoptic pattern of the region in the days involved. The first group is the Siberian High Pressure Tabs, whose cores are located in the confines of Lake Baikal, Balchash and northern Pakistan, depending on the season and synoptic conditions. The low pressure cores are located on the Caspian Sea and the pressure difference between the high pressure tab of the Alborz Outer Slopes and the Caspian Sea causes a compressive stress. In this model, Cyclone currents with increasing moisture of the Caspian Sea on the western slopes of Alborz Heights cause precipitation and warm flow due to warming under windward slopes. The second group is the anticyclone of Saudi Arabia, in which specimens with spin cores are deployed on southwestern Iran. As the north side of the Arabian High Pressure extends northwest of Iran and the presence of low polar pressure in the Caspian region with intensified compressive flow causes currents southwest along the perpendicular heights. Western anticyclone currents in the Arabian Sea circulate the moisture of the southern warm seas to northwestern Iran. The third group is a combination of African anticyclones, immigrants, Siberian highs and its tabs that create a thermal and compressive style over the study area and west of the Alborz Mountains. And provide the basis for the formation of the foehn phenomenon.

Dr Hasan Lashkari, Mrs Mahnaz Jafari,
Volume 8, Issue 1 (5-2021)

Synoptic Patterns that Determine the Trajectory of Precipitation Systems of Sudanese Originntroduction
Precipitation as an important climatic element has many irregularities and fluctuations. Iran, especially its southern half, has significant precipitation fluctuations. Several atmospheric systems are involved in the formation of precipitation in this region from of Iran. Sudanese system is one of the most important precipitation systems in Iran. This system, in different synoptic conditions, enters Iran from different input sources and passes through Iran in different ways.
The important and influential role of Sudan's low pressure on precipitation in Iran, especially in the southern part of the country, has been repeatedly demonstrated in numerous studies. But the formation and its expansion have received little attention. These reasons have led to the consideration of the position of Sudan's low-pressure synoptic expansion as an influential factor in the southern half of Iran precipitation. Therefore, the position of the expansion of this important climatic system has been investigated separately in the precipitation of the three regions south west, south middle and south east.
Materials and Methods
Two categories of data were used for this study. These data include daily precipitation data from the Iranian Meteorological Organization and the ERA interim gridded data include Sea Level Pressure (SLP) and the Geopotential Height of the 700 HP atmospheric level of the ECMWF. Second category data with horizontal resolution of 0.5 × 0.5°  degrees during 1997-2017 statistical period were prepared.
To achieve the purpose of the study, the southern half of Iran was first divided into three regions: South-West, South-Mid and South-East. After extracting daily precipitation of the selected stations in all three geographic regions, a total of 142 precipitation systems was identified by applying the required criteria. From this number of precipitation systems, respectively, were obtained in the south west 107, south middle 19 and southeast 16, respectively. Then, the source of precipitation systems was extracted using the atmospheric lower level maps. Subsequently, the central core and zone of the first closed curve around the Sudanese low pressure were extracted separately for each group. The main axis of the Sudanese low-pressure trough are also drawn on all rainy day. Finally, the model or pattern of atmospheric circulation in the precipitation systems of the regions is presented separately.
Results and Discussion
The purpose of this study was to determine the position of the central core and the pattern of expansion of the first closed curve around the Sudanese system and the Sudanese system trough in precipitation in each of the three regions of the southern half of Iran. Since the arrangement of precipitation systems may vary in different months of the year, depending on the general atmosphere of the atmosphere, the position of the core, the pattern of expansion of the low-pressure trough and the trough of 700-hPa atmospheric level is analyzed separately each month.
In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwest-northeast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally north-south. As a result, the rainfall intensity and intensity of precipitation systems, entering the south west of Iran are higher than the other two routes. The focal point of troughs this route is between 30 to 40° east (Eastern Mediterranean). In systems with South-Mid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeast-southwest axis. In this pattern, the Mediterranean troughs are generally northeast-southwest. This pattern causes precipitation in the eastern half of the Iran. Or at least no precipitation in the northwest and west of the Iran.
The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The troughs of this path showed two completely opposite patterns. In some systems, the troughs in the southwest-northeast direction with the orbital inclination, covers the whole of Saudi Arabia and southern Iran. On the contrary, in some systems the troughs stretch quite opposite to the first group, the northwest-southeast direction.
This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone. Basically Mediterranean troughs are disrupted in their usual eastward displacement after a longitude of 60 degrees. As you can see, the Sudanese low-pressure troughs for the South-East Route lack structural discipline and coordination.
The results of this study show that the location and pattern of expansion of the first closed curve around low pressure in different precipitation months and systems of the three zones do not differ significantly in location. Rather, it is the most important system in determining the direction of Sudanese systems, the Arabian Subtropical High Pressure and the pattern of expansion of the eastern Mediterranean trough. In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwest-northeast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally north-south. In systems with South-Mid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeast-southwest axis. In this pattern, the Mediterranean troughs are generally northeast-southwest. The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The Sudanese low-pressure troughs for the South-East Route lack structural discipline and coordination. This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone.
Keywords: Synoptic Patterns, Sudanese Low Pressure system, Eastern Mediterranean Trough, Southern Half of Iran, Arabian Subtropical High Pressure.

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