جستجوی مقالات مرتبط با کلیدواژه "dust storms" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

According to their specific geographic and climatic conditions, the extent and intensity of dust storms in the west and southwest parts of Iran have made this phenomenon one of the principal environmental hazards in these regions. The extent of dust storms, their significant effects on health, economy, environment, and agriculture, and their increasing trend have drawn the attention of many researchers. The recent study is composed of data analysis of dust storms by Iran Meteorological Organization Earth Database, synoptic analysis of weather and climate patterns causing and transmitting dust using middle and upper atmosphere data in Sanandaj, Kermanshah, and Ilam stations and tracking wind packages carrying dust particles using HYSPLIT model with forward and backward methods.

To analyze atomosphoric patterns, the middle and upper atmosphere data such as the sea level pressure data, level of 500 hPa geo-potential height from NCEP/NCAR databasewere drawn using GRADS software. HYSPLIT model and MODIS images for dust storms.were used to recognize the origin of dust storms and wind flow routing in the stations.

Earth database investigations show that the year 2008 has one of the most extreme dust storms in terms of visibility reduction and durability of days with dust storm in the study period. From 2 to 5 April 2008 the most extreme dust storms with visibility of fewer than 500 meter occured in the stations. The results of wind flow routing by the HYSPLIT model showed that the origin of the dust storm mass was North West of Iraq and east of Syria, which had entered Iran with a north west-south east direction. The middle and upper atmospheric circulation base results show that west winds occurred with a low-pressure center in the East of Iran and high pressure in the North of Africa, causing the entrance of dust to this region. As one of the most intense dust storms of recent years, the mentioned dust storm can help by recognizing atmosphere patterns causing this phenomenon and routing winds transmitting aerosols.

According to the results of this study which has examined the relationship between large scale synoptic patterns and a variety of space-time dust storm activities in Iran using synoptic maps of sea level pressure circulation patterns, 500 hPa geo-potential height of dust storms in the studied stations, and wind flow routing model, it can be concluded that dynamic models can be presented by consensus of various specialists for this destructive environmental phenomenon-although using satellite imagery and dust storm capability and investigating them can be of great importance for future studies. In general, the results of this research show that wind flow routing model and atmosphere studies have the suitable capability for recognizing and monitoring dust storm paths.

Dust storms is one of the most important environmental hazards, especially in arid and semi-arid climates, which causes irreparable damages to the various dimensions of the environment. The aim of this study was to identify dust sources in south-east Ahwaz, using a remote sensing technique and fuzzy logic. For this purpose, the satellite images of dust events of Ahwaz City were investigated and the wind characteristic of the study area were studied by plotting the storm rose of Ahvaz Synoptic Station. In the next step, the criteria were categorized into two categories: soil moisture, land surface temperature and vegetation constitute the main layers and land use, spatial data of soil, climate, slope and sedimentology were used as constraint layers. The main layers were extracted from Landsat OLI-TIRS satellite images. The Boolean method were used to standardize the constraint layers, and the fuzzy membership functions were used to standardize the main layers. Also, main layers weighting was done using fuzzy analytic hierarchy process. Finally, the dust sources map was obtained by overlapping the layer. To validate the results, 44 ground control point were selected from the study area that showed high accuracy (81.8%) for identified areas. Based on investigating of satellite image and storm rose of Ahvaz Synoptic Station, the south-east of Ahwaz was recognized as dust-generating source and 145162.01 ha of lands are dust generating sources from which 69343/01 ha (47.77%) belongs to destroyed rangelands and 335.99 ha (0.23%) belongs to Canebrake, contains the highest and lowest level of sources of dust production in the study area, respectively.

Different regions have various dust production; and the increase of dust storms illustrates the arid ecosystem dominance in each region. Analyzing and identifying of dust storms and its association with climatic parameters is one of the crucial approaches to reduce the caused damage of this phenomenon. Since besides determining the portion of each climate variables in intensifying the circumstances, it also can play a fundamental role in priorities, macro management policies, and upstream rules in order to control and prevent dust particles.  In order to carry out this study hourly horizontal visibility data, World Meteorological Organization codes, hourly dust data, and also monthly meteorological and climatic data including maximum temperature, minimum temperature, average temperature, maximum wind speed, total rain, and soil temperature of different depth (5, 10, 20, 30, 50 cm) in 37 synoptic stations of the country were gathered through a longitudinal statistics of 25 years (1990-2014) and its trend was calculated by non-parametric statistics of Mann-Kendall and Sen’s Estimator tests. After the qualitative analysis of the stations’ statistics and elimination of defects, all the data were assessed via Run Test at the coefficient level of 95%. In order to analyze the effect of climate fluctuations on dust storms, beside the mentioned variables, draught variable of evaporation-rain index and standardized precipitation evapotranspiration index (SPEI) in seasonal period calculated and then Spearman test was applied for correlational analysis of climate elements and dust storms. The frequency outcomes of dusty days during a long-term study of 25 years indicates that Zabol, Abadan and Ahvaz orderly with 711, 401, and 321 days have the most dust storms. The results of Mann-Kendall show out of 37 under study weather stations, six stations of Ardebil, Birjand, Mashhad, Sabzevar, Yazd, and Semnan reported a descending trend. Five stations reported a meaningful growing trend with coefficient of 95% and 21 stations out of the 37 present stations have a growing coefficient of 99%. The result of Sen’s Estimator test shows the six stations which based on Mann-Kendall test had a descending trend, they don’t follow a trend in this method and orderly 11, 10, and 10 stations had a rising trend, significant rise at 95% coefficient level also at 99% coefficient level. Generally, in most cases the results of the two tests had the same coefficient level. The results of Spearman coefficient across the country shows that the frequency of dusty days with the maximum wind speed, SPEI scale, and maximum temperature among the mentioned climatic parameters in order 0.74, -0.57, and 0.48 had the highest coefficient and were all significantly coefficient at the 99% level. Among the rest temperature of different soil depths (5, 10, 30, 50 cm) in all 37 under study stations there is a direct relation with dust storms and were significant with 0.39 at the level of 95%. So, we can conclude the surface levels of soil (5 and 10 cm) have a crucial role in dust storms in different soil depths. The results of this study show, applying two methods of Mann-Kendall and Sen’s Estimator tests are effective for analyzing the long-term changes of dust storms. Generally, the results of Mann-Kendall tests show a rising trend of dust storms in west and south west and some parts of north west and south east of the country. The result of the Sen’s Estimator test says that Ardebil, Birjand, Mashhad, Sabzevar, Yazd, and Semnan don’t follow a trend. As far as the mentioned stations do not have regular dusty days, thus we can consider Mann-Kendall is not a very strong test because of presenting integer results in the stations which contain data of many zeros. The results of correlation between climate elements and the frequency of the dust storm days showed that the highest correlation is related to the maximum wind speed variable with 0.74 as a strong lever for picking up the dust. There is a negative correlation between rain and evaporation-rain index and potential standardized precipitation evapotranspiration with dust phenomenon. This negative correlation is more tangible in SPEI and in most of the stations at the coefficient level of 95% and 99% significant. Thus, as there is more rain in the specified station, there are less dust days. All in all, after maximum wind speed, the SPEI index receives the highest correlation that justifies dust storms. The results also show as we go deeper to the soil layers, the correlation between soil temperature and dust storms declines. The highest and lowest correlation exists in depth of 5.50 cm of soil with the registered numbers of 0.39 and 0.017. The results of this study are useful for recognizing the effect of climate years on the frequency of dust storm and restraining deserts.

Generally, satellite images and climatological and environmental data are used simultaneously in dust storm studies. Most of the processing techniques are limited to a few indices such as brightness temperature differences, normalized dust density index, aerosol optical depth, false color composite and visual image interpretation. Since the reliability of the above-mentioned methods are varied, so an attempt was made to increase the reliability of automatic spatial image clustering by contributing the expert knowledge via visual image interpretation. Therefore, the required satellite images were collected for a period of 2005 to 2008, in Mesopotamian, Syria and south-western provinces of Iran. For doing this, the MODIS color composite images were decomposed into their ordinary bands and then used for further analysis. In this research, spatial image clustering followed by visual image interpretation (hybrid classification) was applied for accurate mapping of geographical extents of dust storm with different intensities. The sources of dust storms were also identified through visual image interpretation by considering the interpretation criteria such as shapes and patterns. Comparison of the previous results and obtained by this research, indicated critical conditions in terms of dust storm occurrence in the region. Image clustering and hybrid classification led to daily dust persistence over the region and then those images compiled in order to prepare annual total heavy dust persistence map. The result of using brightness temperature difference method verified similarity and reliability of obtained results. Therefore, this simple method could be proposed for identification of dust sources, related plumes and their affecting areas, when raw image data are not available.

Duststorms occur generally in Sistan region. So، it limits the development of the region. Many factors play especial role on duststorms such as removal of vegetation cover due to automobile transportation. The aim of this research was to identify car transportation role in producing dust storm. For this reason، three sites with different characteristics were chosen and in each area، two sites of 600 and 300 m length and wide respectively were selected with and without car transportation. Three soil samples were taken randomly from the first، mid and the end of the sites of each location and they were analyzed for pH، EC، CaCO3، organic carbon، moisture، calcium and vegetation cover. The soil erosion measured according to the Universal Soil Loss Equation. The results showed that the car transportation areas have less amount of clay، vegetation cover، topography، soil surface roughness، organic carbon، but، they have an increase in soil small particles with less than 0. 84 mm in diameter، pH، EC، CaCo3and land length which they have especial effect on wind erosion of the region. Results also show that the amount of soil erosion is 15. 8-216. 3 tonsperhectare in study area.

Climate change has become a widespread and relatively dominant phenomenon at present. It has affected many atmospheric processes such as rainfall, dust storms, temperature increasing and so for. These changes are very important for the living environment and thus needed to study and understand. Therefore the main objective of this study is to investigate the temporal and spatial variations of the dust storms over the northwest of Iran. For this purpose the daily data of temperature, rain, dusty days and wind speed of five stations in the area were obtained from Meteorological Organization of Iran for the years 2001-2005. In addition to the temporal analysis of the dusty days the synoptic patterns at the 500 hPa level and sea level and satellite imagery of a case dust storm were analyzed. The results showed that the dominance of a deep trough at the 500 hPa level and a surface low brings the dusts from the west and northwest through the westerly and northwesterly winds to the area. As a result, the main source for the dust storms is the dried and barren lands of Iraq and the main carrier is the atmospheric winds.