جستجوی مقالات مرتبط با کلیدواژه "غرب و جنوب غرب ایران" در نشریات گروه "جغرافیا"

In deserts and dry areas, sudden changes in temperature cause strong winds and as a result cause the phenomenon of dust. The purpose of this research is to investigate the relationship between the occurrence of dust storms and the North Atlantic Oscillation (NAO) index at selected stations in the west and southwest of Iran (Abadan, Bostan, Ilam, Dehloran, Kermanshah and Sarpol-E-Zahab). For this purpose, we used the codes of days with dust storms, horizontal visibility of less than 1 km, data related to index values (NAO) during the statistical period 1987-2022, and satellite data including dust optical depth index (AOD) obtained from the productions of the gauges of 2000-2017 MISR and 2002-2022 MODIS periods. The results of the correlation coefficients showed that there is a relatively strong inverse relationship between the NAO index in the negative phase and a weak direct relationship with dust in the positive phase, and between 51% and 70% of the dust occurrences were simultaneous with the positive phase. The graph of changes in the time series of the indices in the two negative and positive phases showed that the value of the AOD index increased from west to southwest, which is evident in the Abadan station. According to the index produced by the MISR sensor in the years 2011 and 2015 in the positive phase and in the year 2008 in the negative phase, the peak of dust storm activity in all stations and its lowest value are related to the Sarpol-E-Zahab and Kermanshah stations in the years 2002 and 2004, respectively. According to the Deep Blue index obtained from the MODIS sensor, the positive phase of 2022 and the negative phase of 2009 can be separated as the peak of dust storms. The results of the Wind rose and HYSPLIT models showed that the direction of dust storms entering Abadan, Bostan and Ilam stations was from the northwest and southwest and in Dehlorn, Kermanshah, and Sarpol-E-Zahab from the west, and the storms with external origin in these stations were influenced more by the countries of Iraq, Syria and Saudi Arabia.

Climate change and global warming may have direct effects on climate extreme values and temporal as well as spatial variations of these events. Alterations in natural and human communities caused by meteorological extreme events are more significant than those caused by climatic averages. These extreme events widely draw public attention, and are particularly foregrounded by governments and academic communities (An et al. 2019). Given the noticeable consequences of climate extremes, the Intergovernmental Panel on Climate Change (IPCC) organized a team of experts to investigate the challenges caused by extreme events and measure extreme indices (Houghton et al. 2001, Peterson et al. 2002). This team suggested 27 indices to investigate and measure climate extremes. These indices have globally drawn the attention of atmospheric sciences researchers, and many studies have been conducted based on these indices to investigate both past and future events. The literature review indicated that spatial and temporal variations of extreme climate events related to both the past and future have been sufficiently investigated by certain researchers abroad. However, extreme climate events in Iran have been rarely examined. The few studies to investigate the events related to temperature and precipitation extremes in the selected region using temperature and precipitation data and synoptic stations located in Western and Southwestern Iran.

The regions that have been investigated in the present study are Ilam, Lorestan, Khuzestan, Chaharmahal and Bakhtiari, Kohgiluyeh and Boyer-Ahmad, Bushehr, and Fars provinces in Western and Southwestern Iran. These provinces cover 28/9924 square kilometers comprising 17/6% of the whole country area. The data used in this study include average precipitation, and maximum as well as minimum daily temperatures at 28 synoptic stations located in Western and Southwestern Iran in a common statistical period of 30 years from 1988 to 2017. After selecting the stations, the Run Test was used for all the stations and precipitation parameters, and minimum were measured. Subsequently, a matrix of the daily precipitation data and minimum. as well as maximum daily temperatures for was prepared. Finally, extreme indices (26 precipitation and temperature indices as suggested by the expert group CCL/CLIVAR) were measured using programming in the context of the MMATLAB software environment, and the variation process in every index was examined using the Mann-Kendall test. Then, the required maps and diagrams were prepared.

The investigation of temporal variations in the occurrence of warm indices from 1988 to 2017 in Western and Southwestern Iran using the Mann-Kendall test (with a reliability level of 95%) indicated that the total trend of warm indices such as warm nights, warm days, the number of summer days, and the number of tropical nights for most of the stations has been increasing. However, the examination of temporal variations in the occurrence of cold indices using the Mann-Kendall test (with the reliability level of 95%) showed that the total trend of cold indices such as cold days, cold nights, and the number of frost days was declining.The significant finding revealed by the general investigation of the total warm and cold extreme indices in the regions covered in the present study is the prevalence of the warming trend over the examined statistical era. The results of the maximum of one-day precipitation amount and the maximum of five-day precipitation amount indices were also indicative of remarkable precipitation rates in the regions based on these indices. The average was 177 mm (in Kuhrang station). The average was 347 mm (in Kuhrang station). The trend of temporal variations in these two indices was also insignificant in the majority of stations in the regions corresponding to the R99p, R95p, R20mm, PRCPTOT, and CWD indices.

The investigation and analysis of the extreme indices trend revealed that the occurrence of warm extreme events was increasing, while the occurrence of cold extreme events was decreasing in the areas covered in this study. One of the main reasons behind these phenomena has been progressive global warming, particularly since the late 1990s. The results of the present study concerning temperature extreme events confirm previous findings (by Zhang et al. 2005, Alexander et al. 2006, Zhao et al. 2012, Varshavian et al. 2011, Miri and Rahimi 2015, Karimi et al. 2018) stated in some studies that investigated temperature extreme indices. The above-mentioned researchers have also highlighted the increasing trend of warm extreme indices and the declining trend of cold extreme indices in their studies. According to the results obtained by the investigation of the frequency of the occurrence and trend of extreme precipitation indices in the areas covered in this study, it can be asserted that the total precipitation rate has been declining corresponding to the majority of Iranian provinces. However, maximum precipitation rates have been declining from 1988 to 2017 despite exhibiting noticeable extreme amounts. Hence, it could be stated that extreme precipitation events increase, whereas the duration of the wet season shortens. Moreover, the declining trend of the wet days' index and the increasing trend of successive dry days' index in Western and Southwestern Iran could be indicative of the gradual intensification of water scarcity. The results of the present study concerning precipitation extreme events largely confirm the findings reported in corresponding studies (such as Klein Tank et al. 2006, I'm et al. 2010, Jones et al. 2012, Koozegaran and Mousavi Baigi 2015) that emphasized the increased extreme precipitation rate and the decreased amount of total precipitation rate.

As an influential element of climate, precipitation affects human activities and societies. It is thus considered to be the essence of any study conducted as a part of environmental and economic planning. Precipitation in Iran, especially in its west and southwest is affected by thermal, dynamic, and thermodynamic low-pressure centers such as the Red Sea trough. The trough is an extension of Sudanese low-pressure with a central pressure of about 1006 hPa. The Red Sea is stretched in a southeast to northwest direction and thus connects tropical and subtropical regions. Considering the importance of the Red Sea low-pressure system for precipitation events in west and southwest Iran, any change in this system will affect precipitation patterns in the region. Analyzing the activity of this system and resulting precipitation in west and southwest Iran will thus provide more accurate understanding of the climate of this region.

Environmental and precipitation data retrieved from Asfezari national database and atmospheric data (geopotential height) extracted from the European Center for Medium-Range Weather Forecasts (ECMWF) were utilized in the present study. A numerical algorithm was also used to identify the cyclones. The algorithm identified 459 cyclones in the statistical period.

Time distribution of days in which the Red Sea trough is active showed increased activity in summer (198 days) especially August (99 days) and spring (178 days) especially April. However, the Red Sea trough showed decreased activity in autumn and winter. Activities of the Red Sea trough have shown a slightly decreasing but significant annual trend during the statistical period. A sharply and significantly decreasing slope can be observed in summer which results in a decreasing annual trend. Average daily precipitation of the study area in the statistical period ranged from 0 to 2.5 mm. The minimum average precipitation (less than 1 mm) was observed in 29.58% of the study area while maximum average precipitation (more than 2 mm) was observed in 3.64% of the study area. The largest part of the study area (66.87%) experienced an average daily precipitation of 1 to 2 mm. Moreover, 24.28% of the region with minimum precipitation (less than 1 mm) was located in the south and southwest of the study area. This indicates a relatively less severe impact of the Red Sea trough in this area. Around 70.88% of the study area has experienced a precipitation between 1 and 2 mm. Subtracting average daily precipitation recorded throughout the statistical period from the average daily precipitation occurring simultaneously with the activities of the Red Sea trough showed a positive anomaly (more than 0.4 mm) in the north and northeast of the study area. Therefore, it can be inferred that most of the precipitation in this area is originated over the Red Sea. It seems that the presence of the Zagros Mountains has also had a significant effect on precipitation in the study area. Areas with a negative anomaly (less than -0.4 mm) in which precipitation is not affected by the Red Sea trough include spatially scattered regions in Khuzestan, and Kohkiluyeh and Boyer-Ahmad provinces (0.74% of the study area). In other words, precipitation associated with the activity of the Red Sea trough was less than the total precipitation, and thus, most of the precipitation in these regions has other sources.

Results indicated that during the statistical period, minimum average daily precipitation has occurred in south, southwest, and northeast of the study area. Moreover, south and southwest of the study area experienced precipitation simultaneously with the activity of the Red Sea trough. The maximum precipitation in either cases (during the statistical period and also during the activity of the Red Sea trough) has been concentrated in parts of the northwest, west, and east of the study area (along the Zagros mountain range). Significant latitude difference between the north and south of the study area, and existence of the Zagros Mountains and consequently the heterogeneous topography have created two different zones in the study area experiencing minimum and maximum precipitation. In the presence of the Red Sea trough, a higher percentage of the study area experienced maximum precipitation. The frequency of days with more than one millimeter precipitation and their spatial distribution showed that under general conditions, the maximum precipitation has occurred in the north, northwest, west, and east covering 61.11% of the study area. Kurdistan province has recorded a maximum precipitation in more than 3500 days under the influence of different air masses. More than 73% of the factors associated with precipitation in Iran, especially in its northwest, west, and southwest are various synoptic systems (cyclones and short waves) entering the country from the Mediterranean with westerly winds. The minimum number of rainy days during the whole statistical period and also during the low-pressure activity of the Red Sea were also recorded in the southern and southwestern parts of the study area.

Dust is one of the most common climatic phenomena in arid and semi-arid regions of the world The phenomenon of dust is a natural occurrence and occurs in areas with vast areas of arid and desert areas, Lack vegetation and other surface coatings. Due to its presence in the arid and semi-arid belt of the world, Iran is constantly exposed to local and synoptic dust and dust systems. In recent years, the phenomenon of dust in the Middle East has been increasing, Because it is one of the five regions of the world that has the highest dust production . Long periods of drought and inappropriate interventions in nature can increase the likelihood of this phenomenon.
In recent years, the trend of dust events in the west and south of Iran, especially in the spring and summer, has increased dramatically .This phenomenon is affected by certain atmospheric conditions and its distribution can affect the temperature, temperature, precipitation and atmospheric circulation conditions of the area during the months of the year.
In this study, data of 56 years old (during 1961-2016) precipitation, temperature and dust on daily scale from 30 synoptic stations in the west and southwest of Iran were obtained from the country's meteorological organization. In line with this study, MATLAB, ArcGIS and SURFER softwares have been used. In order to analyze the information, recognition of fluctuations and the relationship between dust, temperature and precipitation have been used.
Recognition of fluctuations and the relationship between dust, temperature and precipitation are investigated using regression, spectral analysis and Pearson correlation coefficient. Then it is represented by trend maps, cycles, and correlation tables. The results for the West and Southwest of Iran have been obtained and explained in detail.
The study of the spatial distribution of the trend shows that most of the stations studied in the dust and rainfall have an increasing trend and have been in a decreasing trend temperature. Spectral analysis of dust, dry days, and temperature showed that short-cycle cycles in addition to the most frequent distribution, showed a higher probability of occurrence than long-term periods. In most of the stations studied, the correlation of dust with temperature and dry days has a positive and direct, relationship with the rainfall has a negative and inverse relationship. The local mororan analysis for the spatial autocorrelation of dust with dry days in the western, northwest, northern and parts of the east of the study area has shown a high value cluster pattern (positive spatial autocorrelation). The spatial autocorrelation of dust with precipitation in the northeastern, eastern, and small parts of the southeast and west of the study area has a high cluster pattern (positive spatial autocorrelation). The spatial autocorrelation of dust with temperature in the eastern, western, and small parts of the south of the range has a high cluster pattern (positive spatial autocorrelation).

Due to its specific geographical situation,Iranhas an especial precipitation pattern. In other words,despitehaving a precipitation equal to one-third of global average,Iran experiences a strong fluctuation in its rainfall regime. According to global classifications, floods are considered to be among the most important natural disasters. In recent decades, humaninterferencesin the environment and improper management of land usehave resulted in increasing severity and higher frequency of these natural disasters (Abbas ZadehTehrani et al., 2010: 78). Extreme floodingcaused by climate changeshave resulted in severe damages in different parts of the world during recent decades and the effects of these changes are more significant in dry environments (Negaresh et. al., 2013: 15). Increasing urbanization and constructions has naturally reduced permeable areasin different basins. The resulting impenetrable surfacesare incapable of absorbing the rainfall, and consequently, the total volume of runoff in the city has increased (TaheriBehbahani and Big Zadeh, 1996).

Two typesofground level data and data collected from higher levels of the atmosphere were used in the present study:A) Precipitation data collected during the first ten daysof April 2019 by stations in Western and South Western Iran obtained from the Iranian meteorological organization.B) Data collected from higher levels of the atmosphere including revised geopotential heights, sea level pressure, meridian and orbital winds, omega and especial humidityobtainedfrom the National centre for environmental surveys at Colorado, USA.For synoptic analysis, environment to circulation approach was used to detect heavy rainfall peak periods and then their synoptic dimensions were reanalysed in the spatial range of 10 to 70 degrees north latitude and 10 to 80 degrees east longitude. Based on the analysis ofprecipitation data, April5th and11th,2019 were selected as having the highest rainfall resulting in the highest level of flooding and damage in the western and southwest regions of Iran.

On April 5th,2019 most regions of Iran have receiveda rainfall of more than 20 mm. The maximum levels of rainfall wererecorded in Koohrangstation(187 mm), Izehstationin Khuzestan (155 mm) and Yasoujstation(151 mm). OnlySistan and Baluchestan, Kerman and South Khorasan Province have experienced a stable situation without any precipitation on this day. However, on April 11th,2019, the highest level of rainfall has occurred inwestern stations of the country. The maximumlevels of rainfallon this day were recorded inNahavand and Tuyserkan stations (Hamedan Province) and Noorabad(LorestanProvince) with 126 and 122 mm, respectively. Central and northwesternregions of the country have experienced the next highest level of rainfallfollowing western regions. Figures 1 to 3 show a part of precipitation values in the western and southwestern regions of Iran during rainfall peak periods. Precipitations in more than 16 provinces in the western, southwestern, and central regions of the country have damagedagricultural, economic and social sectors. More than 45 people were killed in thesedays.The highest number of deaths and injurieshas occurred in Shiraz. In the western parts of the country, Poldokhtar and Mamoualn were most severely damaged. Moreover, heavy rainfall and floodinghave damaged 700 thousand hectares of agricultural land and resulted in 4600 billion USDlosses. In the construction sector, the country has suffered from 1,600 billion USD losses (Hamshahri Newspaper, 1398).

The present study have focused on synoptic and thermodynamic analysis of  systems causing pervasive, heavy and hazardous precipitation onApril 5th and 11th in the western and south western regions of the country. The synoptic and thermodynamic analysis of maps indicated that the contrast between the influence of southern and western low pressure fronts such as Saudi Arabia, Sudan and the Mediterranean on the southwestern areas of the country and the cold high pressure frontover the Caspian Sea have caused a strong pressure gradientand formed a strong front condition over the country and the region under study at the sea level. In the middle and upper atmosphere, deep multiple amplitudetroughsformed over the North Pole passed through Russia as bipolar and low pressureblocks, cyclonic centressettled over the eastern Mediterranean regions and the eastern half of the trough formed as a result of blocking settledover the western and southwesternregions of the country. These have resulted in severe, and widespread negative omega and divergence of warm and humid southern weather over the country and the region.

One of the most important environmental challenges which exists in the Middle East and Iran in recent years is the phenomenon of dust. As regards the Western half of Iran is in proximity to large deserts and continually effects the country deserts dust and specially that western half and also the unpleasant effects that these dusts have on environment and people health; so the purpose of this study is the use of Combined method (E-synoptic satellite) for exact recognition of this environmental risk. In this study Terra / MODIS satellite images for dust event of 1 July 2008 West of Iran and the data of Nova Organization database includes: Geopotential height. (HGT) 500 HPa level, the condition of Sea Level Pressure (SLP) and the circuit and Meridional wind components from NECP website have been used. Quantitative indicators of dust detection on satellite images includes NDDI, BTD, BTDI and LRDI indicators, visual dust detection indicators includes false and true color combination and false color combination patterns. The results of applying the quantitative indicators to detect dust on MODIS images showed that the dust indicators and creating the false color image so that it can detect the areas covered by dust directly for dust detection of Iran on MODIS images has enough and good ability. Also the review of synoptic weather map for July 1 showed that the establishment of a low pressure system on Iraq and the south of Persian Gulf and the coordinated deep Landing effect on ascendent area at the same time with Azores high pressure weakens provides the perfect background for dust transfer to the area atmosphere.

In recent years, by intensified desertification in Iraq, Saudi Arabia and Syria, dust storms have affected different aspects of people's lives over the West and southwest of Iran. Atmospheric aerosols affect public health, air quality, energy balance of the Earth and the hydrological cycle. Thus, knowledge of the spatio-temporal dust storm's distribution characteristics is extremely important to quantify these effects. By increasing in dust storms in the West and southwest of Iran much discussion about the various causes of this phenomenon has been increasing. Aerosol optical depth (AOD) is an important remote sensing parameter that serves as a columnar proxy variable representing aerosol abundance. In this study, monthly mean AOD from Moderate Resolution Imaging Spectroradiometer (MODIS) are used to investigate the spatio-temporal distribution of dust storms in these affected areas for the period between 2000 and 2015. Monthly AOD data from the MOD08 Level 3 product (http://ladsweb.nascom.nasa.gov/data) at a resolution of 1° × 1° are used. This study focuses on AOD at 550 nm over land, as this is close to the peak of the solar spectrum and is, therefore, associated with major radiative effects. Synoptic data are examined to identify how well geopotential height, temperature, and wind field at various levels (i.e., sea level, /500/250 hPa isobaric levels) are related to AOD and to dust activity. Meteorological data from the ECMWF archived operational initialized analyses at a resolution of 2.5° × 2.5° (Bou Karam et al. 2010; http://apps.ecmwf.int/datasets/data/interim-full-moda/levtype=sfc) is used.
Results, MODIS monthly mean AOD validation results using the Pearson correlation test to determine the correlation between monthly mean AOD and monthly visibility data indicated high efficiency of AOD products in the dust storm intensity study. To distinguish between the Rub’ al Khali and the influence of factors such as dams in other areas, the study domain is divided in two sections consisting of desert areas in (i) Saudi Arabia and (ii) Iraq-Syria.
AOD plot of the provinces of the west and southwestern of Iran showed provinces of Khuzestan, Ilam, Kermanshah and Kohgiluyeh in order have experienced the highest dust storms from 2000 to 2015.
As the dust storms in all months of the year are not active, to evaluate the spatial distribution of mean AOD per year, the average for the months in which the dust storms are active evaluated (named as annual AOD). Annual and monthly average plots showed that the trend of the amount of AOD in many cases in the deserts of Iraq and Syria desert was similar to deserts of Saudi Arabia.
Considering the wide range of climatic conditions affecting the occurrence of dusty storms, the best way to find out the effect of circulation on the formation of dusty storms is to compare the synoptic state of a special month in two active and inactive periods. To achieve this goal, the monthly anomaly maps (monthly average of 30 years (1981-2010)) were extracted at surface level, 250 and 500 Hp. Two months as representative the active and passive dust storm period was selected to study atmospheric circulation associated with dust. To investigate the impact of synoptic systems on factors influencing dust in the study region, precipitation, temperature a case study analysis of July 2009 and July 2014 was conducted.
Also analysis the map of the average annual distribution of dust in each region shows that the trend of AOD value in many cases in the deserts of the Saudi Arabian desert was similar to Iraq and Syria desert, but AOD value in which years the dust in deserts of Iraq and Syria were still down is high in East and South East Arabian Peninsula. In this study, changes in the behavior of dust storms in the west and southwest of Iran were investigated using quantitative monthly and annual AOD data from 2000 to 2015. The result of the Pearson correlation test with the aim of determining the correlation between the monthly average visibility and mean monthly AOD and indicates the high ability of the AOD monthly data to study dust storms.
Trends of AOD show that from 2006 to 2012 there was increasing trend in February, March, April, May, June and July with a significant slope. The gradient of the monthly AOD slope of Kermanshah province was similar to Iraq and Syrian deserts and also Khuzestan province comply Saudi desert or desert of Iraq-Syria in different cases. These differences can only be caused by differences in atmospheric circulation in different dates.
By comparing the synoptic maps of active and passive anomaly, it seems at sea level pressure existence of Pakistan's low pressure center and increasing pressure on the Mediterranean Sea exacerbated atmospheric turbulence and wind speed in the Middle East play an important role on the intensification of dust storm activities. At the middle and upper levels of the atmosphere, the sovereignty of the subtropical high pressure over the Arabian Peninsula, south of Iraq, the Persian Gulf and the southern part of Iran, also increasing the activity of the Mediterranean waves, increasing the mean wind speed at the upper levels of the atmosphere, as well as the flow of jet stream core has led to an intensification of dust storms in July 2009. That's why limited dust storms have been created in central and eastern regions of the Arabian Peninsula

Dust storm is one of the most important natural phenomena and a kind of severe natural disaster that begins and diffuses under the influence of atmospheric systems. It occurs frequently in desert lands and their surrounding areas in arid and semi-arid regions. The main factors influencing amount of dust in the air are precipitation، vegetation cover، and wind velocity and particle size of soil in source of dust. Over the past decades، Middle East dust storms have caused many problems for the residents of South and South West regions of Iran. Now it is going to change into the main persistent environmental problem in Iran and the Middle East region. The Middle East dust has great impacts on quality of the inhabitant’s lives، visibility and transportation، micro-climate، ecosystem، communication systems and consequent crisis such as، eco – social and environmental problems in the west and south west of Iran. Different aspects of this phenomenon in the Middle East have already been considered by researchers. The aims of this study are to (1) understand the possible source (s) of West of Iran Dust storms and (2) determine the geochemical، mineralogical، trace metals and microbiological characteristics of dust particles in the west of Iran. Study Area: The study area from which sampling was performed، include two provinces of Kermanshah (45. 24-48. 30 E and 33. 36-35. 15 N)، and Khuzestan (47. 42°–50. 39° N and 29. 58°–32. 58°N) which are located close to the Iranian border with Iraq in western Iran. This region comprises 38 cities and a population of more than 6،000،000 people. Topographic elevations in these provinces vary between 0 m (in beaches) and 3701 m (Menar Mountain in Khuzestan province). Fig. 1. The Study Area In this study، five severe dust storms in the west and southwest of Iran have been selected. The air sampling was performed in Ahvaz and Mahshar Cities in Khuzestan province، Kermanshah and Qasre-Shirin cities in Kermanshah province. Dust samples were collected to obtain PST by using the high-volume Air (HVA) samplers (Anderson and TCR models) and the fiberglass filters used to get particles. The flow rate of the HVA sampler was 1 M3/min. Also، for some times the sampling was performed by using Low volume Air (LVA) sampler. After the calibration of air sampler، the particles were got from sampling stations، which were located at urban areas in these cities on the height of 2 meter above the ground. The sampler was run continuously for a period of 24 h. Then، the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model is applied by using a backward trajectory approach in the study periods. The OMI imagery aerosol Index is used to determine the main sources of dust storm. The mineralogy، Sample elemental analyses، toxic trace elements analysis، Microorganisms Analysis of airborne dust samples were analyzed by XRD، XRF، Atomic Absorption and culture-based assays respectively. The outputs of HYSPLIT model and aerosol index from OMI imagery show that main sources of DS1 are the area between the west bank of Euphrates and east bank of Tigris in middle of Iraq، deserts lands in south east of Iraq and north east of Arabian Peninsula. In DS2، the main sources of dust are south and southeast of Syrian Desert، an area between Euphrates and Tigris، Nafud desert in north of Arabian Peninsula، and the coastal region in east of Arabian Peninsula. The main sources of dust in DS3 are South of Syrian desert، North of Arabian Peninsula (Nafud desert)، middle and south of Iraq. The dust sources in DS4 are Syrian Desert، the area between the west bank of Euphrates and east bank of Tigris، deserts lands in south of Iraq and for DS5 are Syrian Desert، desert lands in west of Iraq، the area between Euphrates and Tigris in middle and south of Iraq. The XRD analysis show that in all samples، quartz، calcite، albeit، muscovite، clinochlore and dolomite are common minerals. But other minerals such as gypsum، orthoclase، actinolite and palygorskite are present in some samples. XRF analyses of dust samples show that chemical compositions are SiO2 (34. 82%)، CaO (20. 48)، Al2O3 (8. 44%)، Fe2O3 (4. 36%) and MgO (4. 22%). Based on Atomic Absorption analysis، the average concentrations of heavy metals include Zn، Pb، Cd، Cu، Ni and Co are 472. 2، 109. 2، 10. 4، 52. 0، 111. 2 and 21. 0 PPM respectively. Ambient airborne dust microorganisms including the six bacteria species belonging to the genus Bacillus، Staphylococcus، Escherichia coli، Klebsiella، Pseudomonas and Enterobacter were found in dust samples. Also four fungi species isolated were Aspergillus، Rhizopus، mucor and Penicillium، that is common in environment. The outputs of HYSPLIT model and aerosol index from OMI imagery show that the main sources of airborne dusts for western Iran are dry lake beds and rivers، alluvial deposits and desert lands in Iraq especially the area between the west bank of Euphrates and east bank of Tigris and Hur-Al-Azim lagoon، east، northeast and southeast of Arabian Peninsula، east of Syria and secondary sources of dust storm in the west of Iran with low level quantity are desert land on Africa and Khuzestan province in Iran. The results of XRD analyses show that the main mineral loads are Quartz، Calcite، Gypsum، Albeit، Muscovite، Clinochlore and Dolomite. XRF analyses of dust samples show that the main chemical compositions are SiO2، CaO، Al2O3، Fe2O3 and MgO. Based on Atomic Absorption analysis the mean of heavy metal in dust storm is more than standard level. The microorganism analysis shows that the dust particles are contaminated with bacteria and fungi.

Dust storm is one of the most important natural phenomena and a kind of severe natural disaster that begins and diffuses under the influence of atmospheric systems. It occurs frequently in deserts and their surrounding areas in arid and semi arid regions. So, the major and most persistent sources for dust scattering in the Northern Hemisphere are located in the ‘‘dust belt’’ which extends from 20°N to 30°N and are developed under the subtropical high-pressure subsidence (Kalderon et al., 2009). In the recent years, there has been an increase in the trend of dust storms in the west and southwest of Iran, especially in spring and summer. Now it is going to change into a persistent environmental problem in Iran and the Middle East region. Dust storms have an impact on many aspects of society, such as the quality of the inhabitants` lives, transportation, air pollution, communication systems and consequent crisis such as, eco-social and biological problems. Additionally, dust can play multiple roles in mediating physical and biogeochemical exchanges among the atmosphere, land and water. So the dust storms affect many aspects of Iranian inhabitants especially who live in the western region. There are many reasons for dust scattering in the atmosphere, including the composition and moisture content of soils, wind velocity and distribution of pressure at the surface and atmospheric levels. The aim of this study is to analyze the different synoptic patterns of springtime dust occurrence in the west and southwest of Iran. In this research, for determining the synoptic patterns of dust occurrence in west and southwest of Iran, three types of data were used including: 1) hourly data of dust phenomena and horizontal visibility for 2000-2011 years for 45 meteorological stations in west and southwest of Iran. 2) In order to detect dust, the data of Moderate Resolution Imaging Spectroradiometer (MODIS) sensor from NASA’s Aqua and Terra satellites were used. Since in (MODIS) sensor, bands31 and 32 (11 and 12 micrometer) are within the thermal infrared range, so the brightness temperature difference between11 and 12micronbandsinthespectrumcanbe used for the detection of dust storms from other climatic phenomenon such as clouds.3) Six-hourly global data analysis with 2.5°×2.5° resolution from the NCEP/NCAR reanalysis, including air temperature, sea level pressure, geo-potential height, U-wind and V-wind components, relative and specific humidity and omega from 1000hPa to 200hPa, were used for the preparation of maps and identify the synoptic patterns. The method of the research was based on the synoptic approach. After clarification of the most patterns of dust occurrences, we identified 15 widespread storms in 11-years period. In this paper, by investigating the synoptic patterns of the dust storms, we identified three main synoptic patterns including: Dynamic pattern: This pattern is the main pattern for creation of dust storm in the Middle East and division to westerly trough, coupling block and omega block. When, the emigrant systems of westerly waves are dominant atmospheric phenomena in Iran and its neighbors, the formation of a trough or blocking in the waves in east Mediterranean cause ascendant weather in Iraq or north of Arabian Peninsula which also cause the formation of a cyclone under the upper divergence part in the surface. Increased pressure gradient and formation of the cold or warm front which cause an increase in wind speed in Iraq and north eastern Arabian Peninsula, are basic sources for generating dust in west and southwest of Iran. Finally the lack of humidity in this region will cause dust storm in these regions. Dynamic-Thermal pattern: In this pattern, westerly waves and the emigrant systems caused creation of dust in higher latitude (Iraq), similar to dynamic pattern, but at the same time in lower latitude, in Arabian Peninsula, Sub Tropical high-pressured are dominated and cause stable atmosphere in this region. So, the pattern of dust creation is different from upper latitudes. In this region, dust creation is under the influence of the increase of air temperature and reduction of relative humidity in the surface in east and northeast of Arabian Peninsula. Thus, it causes the development of Persian Gulf low pressure and an increase in wind`s speed and creation of dust. The dusts generated with wind stream line in 700 or 850 HP scatter in southwest on Iran. Thermal pattern: When sub tropical high-pressured are dominated in the Middle East, the increase of air temperature and reduction of relative humidity in the surface in Iraq and Arabian Peninsula cause the development of Persian Gulf low pressure and increase of wind` s speed in this region that is suitable for dust creation In recent years dust occurrence is an important natural hazard in west and southwest of Iran. The annual dust cycle in the Middle east are associated with seasonal occupation changes in westerly winds, rainfall and soil moisture, downward flowing jet stream in cold period and thermal cyclone in warm period. This paper includes the following a) When westerly waves and their emigrant systems are dominant atmospheric phenomenon in low latitudes (Iraq and Arabian Peninsula), these ascendants cause the creation of dust in west and southwest of Iran. b) At the same time westerly waves and their ascendant in upper latitudes cause dust occurrence in Iraq. But in Arabian Peninsula, Sub Tropical high-pressure is dominant and creation of dust is affected by thermal surface low pressure. c) At the end of spring, the Middle East is dominated by subtropical high pressure and subtropical jets stream, but the circulation of the atmosphere during dust storm, shows that a low pressure extends over Persian Gulf and south of Turkey. So, the surface low pressure is the cause of dust occurrence in Iraq or Arabian Peninsula. Basic sources for scattering of dust in west and southwest of Iran are Iraq, desert lands in north and northeast of Arabian Peninsula, East and southeast of Syria, also in some times is Sahara desert.