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Volume 1, Issue 1 (4-2014)
Nowadays air pollution in large cities such as Tehran have dramatic effects on public health, hence study of the way air pollutions varies with meteorological parameters appears to be important. One important aspect of sustainability of large cities such as Tehran, is controlling the emissions of pollutants as the meteorological (climatic) conditions are becoming more acute in terms of air pollution and temperature rise. In this paper some recent records of near surface meteorological parameters as well as some pollutants records are examine to observe how they change daily, monthly and annually and how they are correlated. Considering the variations of winds and temperature (extracted from a 2D sonic anemometer at 10 m at the Institute of Geophysics, Tehran University in the northern part of central Tehran, with one minute intervals) and hurly data of CO and PM10 concentrations for the same station for 2007, their relations were investigated. Also using upper air meteorological data (at 00.00 and 12.00 UTC) from Mehrabad Airport station, the stability of the atmosphere during this period was analysed. Here the buoyancy frequencies that are measure of stability of air column were calculated. For averaging of winds two methods based on the real wind vectors and wind unit vectors were used. By correlations between the pollutants concentrations and meteorological parameters, their relationships were considered. Based on the probability distributions of winds for 2007, it was found that most of the time wind speeds were in the range of 0.5 and 2 m/s. Hence most of the time due to this weak wind there was a condition of air pollution accumulations over the city and only local winds could move the polluted air over the area. Annual cycle of variations of mean surface winds had small amplitude that appears to be due to high mountain ranges that surround the city from north and east. The annual cycle of CO variations showed a peak in autumn and winter while PM10 amounts showed a trough in winter and spring. The higher values of CO in winter seems to be due to the surface temperature inversions and improper burnings of the fuel of vehicles as well as the domestic heating systems. This was indicated in the correlations between temperature and CO concentration. In annual cycle the correlation between CO and PM10 concentrations was about 0.4 which increased to 0.7 for spring time. This may indicate that in this season the sources of these two are similar and one of them may be used to estimate the others is the sources are not changed. There are two maxima in the daily variations of CO which coincides with minima of wind in morning and evening transition times. In this study it was found that due to calm meteorological conditions (often od local origin, called mountain breezes) over the city air pollution problem is a serious problem requiring more emission control. Also trend factors as the pollutant sources (traffic) and the depth of the atmospheric surface layer are important. It is particularly noticeable that during the midday as the depth of the mixed layer increases, the air pollution concentration is reduced substantially. At night surface drainage flow from north of the city and surface radiation cooling creates near surface inversions that can limit mixing and ventilation of the polluted air from the area leading to higher values of gaseous pollutant over the city. Also lager stability in the air over the city at higher levels in autumn and winter is due to subsidence inversions as a result of the prevailing meteorological conditions of high pressure systems over this area in these months. Such conditions seem to have increased the creation of more acute conditions for air pollution over the city. For a more resilient city in terms of air pollution, some mitigation need to be undertaken in the face of climate change effects that are deteriorating the atmosphere of the city.
Volume 1, Issue 2 (7-2014)
Wind erosion is important in areas with less than 150 mm of rainfall Measuring the extent and severity of wind erosion in many countries, including Iran, there is no station to measure wind erosion sediments and so the deposition estimation methods rely on empirical models so that in many cases there are measurement errors. With estimates wind and water erosion and deposition potential compared using IRIFR EA and MPSIAC models in semi-arid Nematabad Bijar watershed concluded that the IRIFR model quantitatively and qualitatively accuracy and, due to a 22.6% wind erosion and 77.4 percent water erosion effective in reducing the fertility of soil (Ahmadi et al, 2006). This study estimates deposition and wind erosion potential using IRIFR method in esfarayen Miandasht region.
In this study, the data collection and basic research in the area uses of maps such as topography, geology, geomorphology, land capability, vegetation, and include information and meteorological studies, field visits, and the prevailing wind direction in the form of desert and question naires were completed and work units to people in another way - specific preparation, IRIFR experimental model of wind erosion in each of the work units were defined the land to wind erosion susceptibility map was prepared using IRIFR and deposition potential temperature using the relationship between precipitation and sediment yield were obtained. After scoring each of the factors affecting wind erosion facies geomorphology (erosion) and the sum of given annual sediment production rates, the rate of erosion severity maps were produced in ArcGIS environment. Soil erosion severity and sedimentation of the area, were obtained nine factors affecting wind erosion scores are considered in five classes.
The results showed erosion class I (very little) with an area of about 11287.21 acres more land erosion. This erosion class is includes geomorphological facies 1-1-2 (water erosion on the erosion piedmont) and 1-2-2 (water erosion on the apandajz piedmont). and class IV (erosion) with an area of 6682.45 acres, is the second largest in the area. This erosional class also includes geomorphological facies detachement region - farm lands – fine desert pavement and the stream. Among stream geomorphologic facies (5-3-2) and arable land (2.3.2) have the most the highest amounts of precipitation.
Wind erosion in the miandasht region, include 8 erosional form and severity of erosion stream facies, etachement region, farm lands and fine desert pavement have high erosion rates. Topography is flat and low-slope land in the north eastern parts of the area where directly affected by the prevailing winds, led to the destructive power of wind improve. One of the best ways to combat wind erosion in the area around the farm and out carminative Miandasht construction area of agricultural land around the study area and the direction of the prevailing winds in parts of the east, the north east is. The study area of wind erosion control perspective is a set of constraints and capabilities. Fine tissue silt abundant salts in the soil and reduces adhesion of soil particle aggregate structure fragmentation and reduce the threshold velocity of wind erosion in the region and the area are prone to erosion. Existence drought resistant species such as Haloxylon prsicum Artimisia sp. in the region can be developed that will help to control wind erosion.
Volume 1, Issue 4 (1-2015)
Mountain systems have an important role on meteorological variations. Different components of the mountain affect the atmospheric parameters and have essential role in atmosphereic circulation. Garmesh wind is one of the most well-known phenomena that are related to mountain systems. In this research, mechanism of garmesh wind are identified using database of garmesh wind in the last 29 years and using remote sensing technology from 2005 to 2010.
To survey the Synoptic and dynamic conditions of atmospheric patterns in the Garmesh wind’s events in the region, SCDATA of several synoptic stations in Gilan province, including Rasht, Bandar Anzali, Astara and Jirandeh are used which had continuous long-term data in 1982-2010period After Identification of days with Garmesh wind, daily images of Modis sensor of terra and aqua satellites in visible band and 7-2-1 band are monitored for checking the cloudiness on the both sides (southern and northern slops) of Alborz mountains and data of Jirande station in southern slop of Alborz mountains are used for detecting atmospheric phenomena like precipitation and snowfall. Also for studying the synoptic and dynamic pattern of this phenomena, reanalysis data from NCEP/NCAR were used.
In this research, Based on the presence or absence of the atmospheric phenomenon (like rainfall and snowfall), three categories were identified. In the first category, Garmesh winds were happened in clear sky conditions and without any atmospheric phenomena on both side of mountain’s slope. In the second category, only cloudiness was seen at the time of the Garmesh wind. In the third category, precipitations (in this research, snowfall) were seen in southern slope of Alborz Mountains.
Statistical analysis of Garmesh wind in central plains of Gilan
Totally, Occurrence of Garmesh wind was 479 days in Rasht, during 1982-2010. The frequency of occurrence of this phenomena was in January, February, November and December and rarely, in September and June. Clouds that observed in the time of Garmesh wind were: Altocumulus (type 4), Cirrus, CirroCumulus.
Patterns of Garmesh wind mechanisms on western half of Alborz Mountain:
- B1. Garmesh wind without any phenomena
This category includes11 cases of total 47 studied cases. 29 January 2008 is an example of clear sky condition in the time of Garmesh wind. In this pattern, in the surface zonal extension of Mediterranean dynamical low pressure’s contours from west of Caspian to Gilan plain and at the same time formation of cold high pressure cell on Zagros mountains caused strong pressure gradient on southern coastal zone of Caspian Sea, As it led to the the increase of wind velocity in Rasht airport synoptic station from 11 kilometer per hour in 00 UTC to 36 kilometer per hour in 12 UTC. Dominance of warm core on southern Caspian versus dominance of cold surface air on Iran Plateau indicates adiabatic warming in northern slope of Alborz Mountains.
- B2. Garmesh wind with cloudiness
This category includes 34 cases of total 47 studied cases. Free of air mass’s patterns in the surface and conditions of atmospheric flows in low-troposphere that are similar to previous category, transition of height trough in mid-troposphere and high-troposphere can be name variant component verses previous category.
- B3. Garmesh wind and precipitation (snowfall)
This category includes 2 cases of total 47 studied cases. At the same time, surface high pressure was on Iran Plateau and low pressure system was on Caspian Sea and also Gilan providence that caused the formation of Northerly stream and west-east stream to southern coastal zone of Caspian Sea and backward of Alborz Mountains like other patterns, snowfall occurred on southern slope of Alborz Mountains. Strong southern and south-western stream and strong positive vorticity on southern slope of Alborz Mountains by deep height trough in low-troposphere has an important role on intensification of vertical motions on lee ward of Alborz Mountains.
Garmesh wind is an atmospheric phenomenon that occurs as a result of interaction between atmospheric systems in synoptic scale and topography on back ward of mountain. In the other words, existence of Alborz Mountain’s as a great wall has an important role in the interaction between synoptic systems and formation of Garmesh wind.
Formation of Garmesh wind phenomena in Gilan province, is affected by extension of Siberian high pressure’s counters and sub-tropical high pressure on central of Iran Plateau and also existence of advection of pressure’s counter like sub-polar low pressure and or the Mediterranean Sea on north of Alborz mountains are required. Without any notification to origin of air masses, three categories has been observed based on existence or absence of Phenomena (in this research, sowfall)
In 700 and 500 hPa, Geopotential height patterns and relative vorticity field indicate that in the first category, wide parts of Iran is affected by high height and negative vortisity like low troposphere, during peak hours the wind. But in the second and third category (specially in third category ) existence of upper trough and easterly extension of trough caused to reduction of height and formation of strong positive vorticity in upper level and all over of air column in both south and north slopes of Alborz mountains.
Volume 7, Issue 1 (5-2020)
Identification of the factors influencing the hazards and the difference in the volume of sediment accumulated in the villages of Nimroz
Abstract
Seasonal lakes or playas are considered as a major source of wind sediments and dust storms due to locating in post-topographic areas in dry and desert areas with strong winds system and also the presence of fine-grained and separated particles. Sediments and wind deposits in Sistan have caused the lives of thousands of people in these areas and especially the students to be at risk. The volume of wind sediments in this county has been multiplied in the last ten years; therefore the purpose of this research is to identify the effective factors on the volume difference of accumulated wind sediments in the schools of the villages of Nimroz County. The research method in this study is quite field and as direct observation, besides library resources has also been used. After the initial investigations, it was found that the geographical location, type of soil and topography have little effect on the volume difference of accumulated sediments in the studied schools. The findings of the study show that the three factors in Bash Delbar area, Hamoon Lake and lack of agriculture and the lack of vegetation in Deh Isa area are the most important factors in increasing or decreasing the volume of wind sediments.
Keywords: wind deposits, primary schools, Human Beast, the lake plain, the city of Nimroz
Volume 7, Issue 1 (5-2020)
Proper design of the central courtyard in residential areas against Sadobist-roz-e winds in Zabol using CFD analysis
Saeide Khaksefidi - Ma Student of Architecture, Faculty of Architecture and urban planning, Jundi-shapur University of technology, Dezful, Iran.
Behzad Vasigh* - Faculty of Architecture and Urban planning, Jundi-shapur University of Technology, Dezful, Iran
Mohsen Taban - Assistant Professor, Faculty of Architecture and urban planning, Jundi-shapur University of Technology, Dezful, Iran
Abstract:
Wind erosion occurs in many arid, semiarid and agricultural areas of the world. Sadobist-roz-e winds are common phenomena in arid and semi-arid areas. In recent years, Sadobist-roz-e winds frequencies and intensities have increased significantly in Iran. A research on Sadobist-roz-e winds sources is important for understanding the mechanisms of dust generation and assessing its socio-economic and environmental impacts. Deserts are the main sources of emitted dust, and are highly responsive to wind erosion. Low content of soil moisture and lack of vegetation cover lead to fine particle’s release. The wind in the eastern part of Iran, Sistan, is one of the most important phenomena in the ecological studies. The intensity and velocity of the wind, has caused environmental problems. This population is distributed in more than 1000 cities, villages and nomadic settlements. Sadobist-roz-e winds is the most significant wind in the region which starts every year at the end of the spring and lasts all through the beginning of autumn, with a mean velocity of 100 km/h. Architecture and urbanization of the Sistan region have been built with the focus on reducing the amount of sand. The orientation and placement of buildings can be effective in reducing the damage to these winds. Sadobist-roz-e winds has increased in zabol since 1999. The average annual number of dust Storm events increased from 10 d during 1990–1998 (before the drought) to 54 d during 1999–2004 (after the drought). The frequency of dust storms also increased 5-fold after 1999 in the region. This shift is associated with an increase in wind speed, rainfall reduction, drying of Hamoun Lake and drought occurrence. The purpose of this paper is to determine the type of obstruction, orientation and enclosure level of the central courtyard so that it can be useful in two areas: wind speed reduction and reduction of dust contamination in the building area. Modeling of buildings is done using 3D software; and simulation of airflow using “Flow3D” Fluid Simulation software has been investigated. Each time the flow of air was tested in different models. First, two main patterns that were expected to be appropriate to the behavior of the wind were selected. Both of them were simulated and it was found that the concave shape has a better performance. Because in addition to reducing the wind speed, it also causes rotational movement. Then, with emphasis on the central courtyard, various shapes of the layout of the builders in the central courtyard were examined. The result showed that due to the high initial wind speed, in addition to the inflow and outflow contours (in the enclosure court), the positioning and orientation of buildings at different angles, it can also be effective in reducing wind speed and decreasing wind movement. By extending this collection to more buildings and creating congestion conditions, the comfort conditions for the pedestrian were examined. In the following, with a constant elevation of 9, and enclosure (H / D ratio) and wind input to a set of 3, this load was simulated with different angles against the wind. Every time the wind speed and the wind velocity decreases. The best location was selected at a 45-degree angle faced to the wind. Further, with regard to the fact that high wind speeds are observed in the best building layout, natural obstacles were used to reduce wind speed. Among the native trees of Sistan, “Gaz” were selected because of their highest adaptability to the region's climate and for research purposes. Physical characteristics were taken and modeling was done. Each simulation was performed; the best model with a natural barrier against the wind region was identified. Although the research on locality could be highly generalized, the best location in the study, which was close to the definitions, was approached. At last, the results show that buildings or obstacles that are concave to the wind direction are more likely to prevent wind entering the shadows area than most other building types. The type of layout and orientation of the buildings against the wind and the amount of enclosure at the two points of “entry and exit of the wind”, along with the use of natural obstacles, can be very effective in reducing the wind speed and reducing the entry of dust to the comfort level.
Keywords: zabol, sadobistroze winds, CFD simulation, Residential complex, central courtyard
Volume 7, Issue 2 (8-2020)
Occurrence conditions for severe snow blizzard in the west-north of Iran
Abstract
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
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.
Volume 7, Issue 4 (2-2021)
Mesoscale Convective Systems (MCSs) are the convective precipitation structure that is most frequently associated with floods at mid-latitudes, mainly due to the high degree of organisation, which allows the structure to be maintained for a longer period of time and to become more extensive. Moreover, MCSs are an important link between atmospheric convection and larger-scale atmospheric circulation. Based on the results of previous studies, it can be claimed that Sudanese low pressure systems in many cases are the cause of the formation of MCSs, especially in southwestern Iran. Although many studies have been done in Iran on these systems and how they are formed, but the role of some environmental components of their formation and intensification, such as vertical wind shear, High and Low Level Jets (HLJ and LLJ) has received less attention. Therefore, the purpose of this study is to investigate the role of these factors in addition of the known factors that cause the formation of these systems. For this purpose, the flood of 24 and 25 march 2019 in the south and southwest of Iran has been selected as a case study.
To track and investigate the spatial characteristics of MCSs in this study, IR channel of the second-generation Meteosat imagery (MSG) on March 24 and 25, 2019, with a spatial resolution of 3 km and a temporal resolution of 15 minutes from Eumetsat site was extracted. After calibration and georeference of the images, the brightness temperature was calculated. The exact choice of temperature threshold for the identification of convective systems is optional and depends on the spatial resolution and wavelength of imagery. The size distribution obtained from the 207 or 218 k thresholds are not very different, especially for larger convection systems. Therefore, in this study, a threshold of 218 degrees Kelvin was used. Also, there is no agreement among researchers on the criterion of minimum length or area in the definition of MCSs, and this criterion is mostly determined by the characteristics of the region and the selected temperature threshold. In this study we select a threshold of 10 thousand square kilometers. In other words, the system was identified as MCSs, which at some point in life had an area of more than 10,000 square kilometers. The daily precipitation data of GPCC database were used to investigate the scattering of precipitation produced by these systems. Also, to understand the synoptic and environmental conditions of occurrence of MCSs on studied days, first geopotential height data, zonal and meridional wind components, potential temperature, relative humidity, vertical velocity and CAPE from ECMWF database were extracted and then the required maps and diagrams were prepared to synoptic and environmental analyses.
In general, the results of this study showed that three MCSs on March 24 and 25, 2019 affected different parts of Iran. The maximum area of the cold core of the first system is about 73,000 square kilometers and has traveled from west to north of Iran. The second system, which affected Iran from the west to the northeast, had a maximum area of about 660 thousand square kilometers. The cold core of the third quasi-stable system with a linear extension (northeast-southwest) and a maximum area of about 440 thousand square kilometers, has moved slightly to the southeast.
The synoptic conditions of the formation of these systems have been the same as the common pattern of the formation of Sudanese low pressure systems and MCSs. In this pattern, Azores high pressure can bring the cold air of the high latitudes to the middle latitudes and hot and humid air is injected by the high pressure over the Oman Sea and the Arabian Sea, which activates the Red Sea convergence zone along with the Mediterranean system. These conditions have led to the formation of the minimum potential temperature zone in the eastern Mediterranean with significant temperature and pressure differences compared to its environment, resulting in the formation of LLJ. This LLJ has been very effective in transferring hot and humid air to western Iran. So that in the peak hours of convective activity in the center of Iran, a potential temperature difference of about 30 degrees Kelvin with the environment has created that has played an effective role in the formation of convective storms. The transfer of hot and humid air by the LLJ has led to the formation and continuation of convection and the release of latent heat to enhance the convergence and longer life of convection systems. On the other hand, the coupling of LLJ and HLJ, by strengthening the MCSs in the western part of Iran and strengthening the divergent flow at higher levels, has strengthened the HLJ, which in turn has led to strengthening the convective system. Vertical wind shear probably also led to the formation of new convective cells in areas far from the origin of the primary convective cells. During the peak hours, unstable convective activity was observed over a large part of Iran, especially the southern and western parts, and its maximum was observed from the southern half of the Red Sea along the convergence zone to the west of Iran.
Therefore, various components of the Sudanese low pressure system play an important role in the formation, continuity and development of mseoscale convective systems. It seems that low-level jet, vertical wind shear and its interaction with the Red Sea convergence zone and the outflow of primary convective cells have a very effective role in the occurrence of this phenomenon. Thus, more detailed studies of this issue using mesoscale numerical models will probably identify unknown aspects of Iran's climate.
Volume 8, Issue 2 (9-2021)
Potential dangers of drought in Shadegan wetland and Identify areas affected by dust from it
Introduction
Shadegan wetland is located at the end of Jarahi watershed. This wetland is one of the most important international wetlands registered in the Ramsar Convention, which is currently undergoing ecological changes and is still on the red list of the Montero Ramsar list. This wetland is extremely important due to its high biodiversity and various functions such as flood control, air conditioning and soil erosion control, habitat of various plants and animals and providing livelihood for a part of human societies. One of the most important functions of the wetland, according to the findings of the present study, is the important role of Shadegan wetland in preventing the production and control of fine dust. There are 143 wetlands in Iran, of which 25 are registered in the Ramsar Convention. Shadegan wetland is one of the wetlands of Ramsar Convention, which in the last decade, a large area of it has become dry and has become a center of dust. In this research, it is important to know that in case of drying of Shadegan wetland, which areas in which seasons will be more affected by dust due to atmospheric currents.
Data and methodology
In this study, the boundary of the wetland was determined based on the highest water advance line during a 30-year statistical period (1988-2017). According to satellite images, the border of the wetland has been determined to be about 164,000 hectares based on the rainiest year and month. Wetland area changes were used to monitor the water level of Shadegan Wetland through Landsat TM, ETM + and OLI satellite data from 1998 to 2017 in the period of June. Three stages of preprocessing, processing and post-processing were performed on the images and supervised classification by support vector machine (SVM) method was used and the images were classified into three classes of water, vegetation and without cover or soil. On the other hand, the classification accuracy for the images was calculated using two indicators, overall accuracy and kappa. To calculate the dry area of the lagoon, floor changes without cover were calculated. The most important cities around Shadegan wetland, which in case of wetland drought may be most affected by wetland dust due to proximity and proximity, and have socio-economic importance and the center of the province and port status, were identified. In this study, the cities of Ahvaz, Abadan and Mahshahr were identified and studied as areas affected by wetland dust during drought. In order to study the role of drying of Shadegan wetland in the dust of the surrounding areas, seasonal and annual dust mites were prepared and drawn. Data on the direction and speed of hourly winds along with the dust were used. Then, using WR-PLOT software, in addition to the annual long-term total rainfall, the seasonal distribution of the direction and speed of events was extracted and the rainfall related to each season was plotted and analyzed, and areas affected by drought in different seasons of the year. Wetlands with greater impact were identified.
Result
The trend of 30-year changes in the soil cover of Shadegan wetland is increasing in total, so that according to the freshwater area of the wetland, which was obtained in this study 164 thousand hectares, 22960 square kilometers has been added to the dry area of the wetland during these 30 years. The largest soil area of the wetland in 1994 was about 87.4% of the total area of the wetland. The lowest soil area of the wetland in 1998 was about 19%. Sugarcane projects have entered the wetland from the north of Shadegan Zahab Wetland since 2002, but due to widespread drought, it has not been able to increase vegetation and reduce the soil area of the wetland.
During the long-term statistical period, spring is the predominant period of pollination in Ahvaz western synoptic station and secondarily in the northwest. The southeast direction is of third importance, but nevertheless, the dryness of the north and northeast parts of the wetland can affect the south and southeast of Ahvaz in this season in Abadan synoptic station. Drought on the west side of the wetland is not a threat to the city of Abadan. In Mahshahr synoptic station, the predominant direction of long-term seasonal rainfall is northwest. In case of drought, Shadegan wetland will be affected from the northwest. During the long-term statistical period, the summer season was dominated by dust and affected in three stations, such as the spring season, with the difference that in this season, dust is more abundant. During the long-term statistical period, autumn is the predominant direction for flowering and is affected in three stations such as spring and summer, but in this season, the southeast and south directions are more intense and frequent than spring and summer.
During the long-term statistical period, winter is the predominant period of pollination in Ahvaz synoptic station, west and secondarily, northwest. The southeast and south directions are of third importance, but in this season, the southeast and south directions are more intense and frequent than other seasons. In this season, due to the expansion of the westerly wind to the lower offerings, unstable atmospheric systems enter Khuzestan from the south and southeast and bring dust with them from areas such as western and southern Iraq and northern Saudi Arabia, and to the southeast. Northwest and passing through the dry parts of the lagoon and the active dust center of the southeast of Ahvaz, the metropolis of Ahvaz will face problems caused by dust in this season. Due to the cold weather and the inversion phenomenon, the dust of this season, which is associated with wetland and inland resources, has a greater impact on the field of view and causes great damage to the equipment and infrastructure facilities by subsiding on the city of Ahvaz.
Conclusion
Drying of wetlands due to various climatic or human factors can lead to increased dust activities. When a wetland dries out, the salts that settle in it become sources of dust. Wetland fine-grained sediments with air velocity less than the erosion threshold due to small diameter and large volume enter the air streams and are dispersed in the air. Active dust centers in the southern half of Khuzestan province have the largest area in the whole country. Shadegan wetland is bounded on the north by the dust center of the south and southeast of Ahvaz with an area of 185043.3 hectares and on the west by the center of the south of Horalazim and north of Khorramshahr with an area of 258916.4 hectares and on the east by the dust center of Mahshahr - Omidieh Hindijan with an area of 254654.4. Shadegan wetland joins the southeastern center of Ahvaz in case of drought from the north and northeast, as if parts of it, known as Hor Mansoureh, have become part of the southeastern center of Ahvaz in the last decade due to several droughts. Is. From the west, parts of it are connected to the dust center north of Khorramshahr and join it if the drought continues. It is connected to Mahshahr-Omidieh and Hindijan centers from the east. In recent years, parts of the wetland and dust centers have overlapped. If the wetland continues and dries, for natural and managerial reasons, more parts of the wetland will dry up and become dust centers and affect important population, political and port cities of Khuzestan Data and will face irreparable social and economic losses.
Keywords: Dust center, dust, wind direction and speed, Shadegan wetland, Right of water
Volume 8, Issue 2 (9-2021)
The daily cycle of radiant heating from sunrise and sunset leads to the daily cycle of tangible and hidden heat fluxes between the earth's surface and the atmosphere. These fluxes, which cannot directly reach the whole atmosphere, are confined to the shallow layer near the surface, called the boundary layer of the atmosphere. . The processes that take place in this layer are important in various aspects such as the dynamics of fluxes and atmospheric systems, surface radiation, the hydrological cycle, and air pollution research. The thickness of the boundary layer of the atmosphere varies with time and place, and its size varies from a few hundred meters to several kilometers on land under different conditions. This thickness depends on various factors such as the type of atmospheric systems and their structure, surface fluxes, steep vertical arrangement and wind direction and surface cover. The depth of the boundary layer can be calculated by different methods. This depth, which indicates the thickness of the turbulence zone near the surface, is usually called the depth of the mixed layer or the depth of the mixture. The methods used to determine the boundary layer of the atmosphere or the depth of the mixed layer are commonly used to investigate air pollution. Estimating the depth of the mixed layer is one of the most important parameters in the pollutant diffusion model. Therefore, the purpose of this study is to investigate the causes of monthly fluctuations in the height of the western border layer of the country with respect to the barley station above Kermanshah.
Materials and methods
Data on inversions of Kermanshah meteorological station during February and August 2012; Obtained from the Meteorological Organization of the country. Also, the data related to the vertical barley survey in this station, which were collected by radio sound, were used and the statistics of daily vertical barley survey above the Kermanshah synoptic station were obtained from the climatic database of the University of Wyoming. After obtaining information about vertical barley survey in Kermanshah station, Skew-T diagram, indicators and profile information of atmospheric conditions were drawn to recognize the dynamic and thermodynamic status of the atmosphere during the selected days in RAOB software environment. Then, in order to study the lower atmosphere more accurately, the changes in the vertical index of potential temperature, using daily radiosound data, the curves of potential temperature changes in terms of altitude were plotted. Then, using Huffer's computational method, days with critical inversion at potential temperature were found. Then, using geopotential height, wind and vertical ascent (omega) data, the synoptic causes of boundary layer depth fluctuations (mixed) and the effective factors were investigated.
Results and discussion
The main purpose of this study is to implement Hafter's proposed model to investigate the monthly fluctuations of the height of the boundary layer of Kermanshah station. The results of using Hafter method in estimating the depth of the mixed layer of the city and its daily changes for Kermanshah station in August and February 2012. In this regard, the effective factors in minimizing and maximizing the mixed layer in every two months (August and February), including: the synoptic situation in the study area on selected days, heat transfer, humidity, vertical arrangement and wind speed were investigated.
Conclusion
The results showed that in August, the depth of the layer during the month was between 3680 to 10292 meters. In this month, temperature subsidence, type of synoptic systems and vertical wind arrangement have directly played a significant role in the growth or weakening of the layer. Considering the comparison of the role of effective factors in maximizing and minimizing the depth of the boundary layer in August, it can be concluded that all factors have a positive role in maximizing the depth of the mixed layer; while the vertical wind arrangement plays an essential role in minimizing the layer depth in this month. In February, the depth of the mixed layer was about 2273 to 7017 meters and significant fluctuations in the values of the depth of the mixed layer were observed during the month. In this month, temperature subsidence, vertical wind arrangement and synoptic systems have been effective in changing the depth of the mixed layer. Comparing the results obtained from both months, it can be said that the amount of surface flux is higher in summer than in winter; thus, the average depth of the mixed layer in August has almost doubled to February. In general, it can be concluded that the depth fluctuations of the mixed layer in winter due to the passage of different systems and the occurrence of atmospheric instabilities, have more changes than in summer.
Volume 9, Issue 2 (9-2022)
Predicting the average annual maximum wind speed in Sistan region using spatio-temporal regression method
: Abstract
The wind is a quantitative vector that moves from high-pressure centers to low-pressure centers and is measured by two factors, the direction of the wind, which originates from the north and increases in degrees clockwise, and the wind speed, which is the horizontal flow. Air is measured in units of time. The wind speed can move colloidal particles, including clay and silt, from the site of destruction to a distance of hundreds of kilometers. Studies show that most dust days occur in the eastern regions of the country so that in the range of 120-day winds in Sistan, the frequency of dust per year reaches more than 150 days. Moreover, the prediction of numerical values of maximum annual wind speed using the Spatio-temporal regression method was considered in this study. Error variance and alignment analysis using variance inflation index showed that numerical models of the Spatio-temporal regression of data could predict the Average maximum wind speed in the coming years. The results also show that regression Spatio-temporal until 2022 can predict wind speed.
The numerical model indicates that the lowest annual average wind speed from 2019 to 2022 is related to the Ghaen station. Its forecast trend shows that by 2022, the average annual wind speed will decrease. The highest annual average wind speed is related to Zabol station, in which the forecast trend of this station shows that the average annual wind speed will decrease by 2022.
Keywords: Spatio-temporal regression, Wind speed prediction, Sistan region
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