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Volume 3, Issue 1 (4-2016)
Dust particles consist of important aerosols and resulting in blowing strong winds on the surface of desert areas. These particles enter the atmosphere under the influence of different factors including: weather condition (wind, precipitation and temperature), land surface (topography, humidity level, roughness and vegetation), soil features (texture, density, composition and land use (agriculture).
Today powerful dust storm destroys people lives and causes severe damages to their life and also causes financial problems in most regions of the world especially in west and southwest of Asia. Dust storm is one of the most important natural phenomena and also a kind of severe natural disaster that influence Iran and its west and southwest part. The location of Iran on the desert belt is accompanied by frequent increasing of sand and dust storm. Integral prediction of dust storm phenomena can be useful in decreasing damages caused by these storms. So synoptic-dynamic analysis of dust storms and their simulation play an important role in achieving to this goal.
In this research, we investigate severe dust storm in August 2005 that affected a large area of our country. Select of dusty days were based on minimum visibility and maximum durability of that dust storm. At first, we show the minimum of daily visibility table. These data has been provided by Meteorological Organization in 5 western cities. The synoptic maps were related to these phenomena derived from NOAA website and synoptic and dynamic interpretation has been done. We have got the data with resolution of 2.5 degree from NOAA website.
Then 700 hpa relative vorticity maps were drawn. We investigate MODIS images instrument on Aqua satellite and evaluate the amount of mass concentration of dust particles. Then the Lagrangian Integrated Trajectory Model has been used to determine the backward trajectory of dust particles. We run HYSPLIT model by GDAS data with a resolution of 0.5 degrees. At last we investigate the output of the WRE-CHEM model. This model was run to simulate dust storms in 7-10 August and FNL data with a resolution 1 degree use for initial and boundary conditions. WRF-CHEM is used to simulate dust condition and transmission. As a part of WRF model, its main application is the study of atmosphere chemistry.
At 500 hpa a very strong ridge entered Iran from the southwest. It covered all areas of our country which prevents the transference of dust to high levels of atmosphere. In 700 hpa relative vorticity maps show one day before dust storm reach to Iran a Positive voriticity is located in Iraq and Syria. So dust comes up to higher levels of the atmosphere and in dusty days in our country. There is a negative voriticity located in our country and because of downside movement of the air, dust storm happen in Iran.
Dust loading and friction velocity of outputs of the model has been drawn in dusty days. The time series of dust concentration of output models for Tabriz are compared with the concentration data of Environmental Organization of visibility data. Result show that a low pressure system is located over the Oman sea that its blaze has been extended to the northwest of Iran. On the other hand a high pressure center is located in the Europe that extended to the east of Mediterranean. So strong pressure gradient were in Iraq and Syria and they caused the creation of strong winds in their deserts which caused dust emission.
Friction velocity related to the model outputs show that the velocity of wind is high in dusty days in Iraq and Syria. So conditions are suitable for dust raining. Satellite images showed that WRF/CHEM model is simulated very well in emission, source, diffusion and the extent of the areas covered with dust. Comparing MP10 concentration of the model output with and Environment Organization data of Tabriz city show that WRF/CHEM model forecast daily changes well. But model underestimate significantly in quantity of concentration. This error may be due to a model considering only dust quantity but other pollutants affected on visibility. In general it can be said that in this event, dust concentration has been underestimated by WRF/CHEM model especially in maximum amount of PM10 concentration.
Volume 5, Issue 2 (9-2018)
Dust phenomenon is a natural occurrence that occurs widespread in arid and semi-arid regions of the world, especially in the sub-equatorial latitudes. This phenomenon is among the greatest environmental problems in the world. The release of this destructive climatic phenomenon in a scattered manner in the atmosphere varies in size, time and concentration. Since this phenomenon is influenced by the specific conditions of climate effects, its effects may continue to be as close as 16,000 kilometers from the source and cause abnormal environmental effects on the one hand, and numerous damage to agriculture, industry, transportation and telecommunication systems on the other hand. Dust storms, as an atmospheric destructive phenomenon, have created adverse environmental impacts for the west of Iran and caused many problems for the inhabitants of this region. Therefore, studying this phenomenon is necessary in order to achieve a comprehensive approach to deal with it. The present study was conducted with the aim of identifying the instantaneous atmospheric conditions, conduction and source of the dust storms with a synoptic modeling approach.
In this study, in order to investigate the dust storms structure in the southwest of Iran, the dust storm occurred on May 15, 2015 was selected. The reason for choosing the present day, based on reports from the Observatory and Monitoring Center of Ilam’s Environmental Protection Office, was the most polluted day of 2015, so the amount of aerosol recorded was 1200 µg/m3 in the air of Mehran City. To analyze the storm structure, a combination study was performed using NECP/NCAR reanalyzed digital data and output of dynamic and regional models. The first group consisted of three regional models of NAAPS, DREAM 8b and NMMB/BSC, and the second group included HYSPLIT dynamic model with backward method. NECP / NCAR data are also used in the synoptic analysis of the storm.
The average slope of air pressure in the sea level at the time of the dust storm in the west of Iran has increased and a high pressure difference of 20 hPa is observed between east and west of Iran, which is accompanied by a high pressure difference and severe winds in the southwestern borders of Iran. Also, the surface moisture flux of the soil has fallen sharply for the day of the storm occurrence in the study area. High advection in the Western part of Iran has been accompanied by a change in the density and mass of the air with heat, resulting in very rapid and intense air rotational movements around the Earth's surface; on the other hand, the coincidence of the positive and negative vorticity in a single significant amount in the formation of the lower level jet has caused the emergence of the dust storm to occur in the mentioned day. On the day of the dust storm, the orbital component of the wind speed was Western, and its velocity was more than 5 meters per second on the western borders of the country. The meridian component of the wind speed was also Southern. Therefore, the effect of present pattern on west of Iran during the day of storm dust has played a significant role. The optical depth index and surface dust concentration index in the NAAPS model have shown that dust concentrations ranged from 640 to 1260 µg/m3 to the west. Besides, the amount of sulfate in the region was estimated to be between 1 and 2 µg/m3. Comparison of the output of DREAM Bb and NMMB / BSC models showed an increase in concentration values per Dust surface unit on the day of storm occurrence. Based on the results of two models of DREAM Bb and NMMB / BSC in the case of western dust in Iran, it can be concluded that the effect of local factors and close proximity to the centers of the dust source have a significant role in the occurrence of present phenomena for western Iran. The simulation of the Dust storm direction with the HYSPLIT dynamic model and the backward method has shown two routes of dust entering the west of the country; a) Northwest - Southeast; b) West-East direction. The main origins of the first route, the northwest of Iraq and the east of Syria, and the second route were the center of Iraq.
Keywords: Spring dust storms, Regional modeling, HYSPLIT model, particles optical depth, West Iran
Volume 8, Issue 4 (1-2021)
Identification of dust centers and, of course, the behavior of this phenomenon in different regions creates one of the problems of the last few decades, which is investigated as a hazard. To this end, statistics from 15 meteorological stations in the northeastern region of Iran, including North Khorasan, Razavi Khorasan, and South Khorasan provinces, were used over a 17-year period (2016-2000). To clarify the mechanisms governing dusty days, the meridional and zonal wind components and geopotential height were obtained by referring to the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). HYSPLIT model and MODIS AOD values were used to track and identify dust centers. The results showed that during the warm season, due to the establishment of a strong quasi-stationary blocking system in the lower levels of the atmosphere, negative vorticity increased in the maximum air descent area, ultimately leading to the dominance of a northern flow for the region. Anomalies in geopotential height and vorticity were identified, and three dominant abnormal patterns were found in the occurrence of maximum dust storms in the region. An increase in geopotential height of more than 5 to 10 geopotential meters and an increase in negative vorticity are considered major conditions. By examining the tracking model and using satellite data, five main centers that affect over 90% of the region's dust storms were identified, among which Turkmenistan has a significant role with two separate centers and one common center with Uzbekistan in the occurrence of summer dust storms in northeastern Iran.
Volume 9, Issue 4 (3-2023)
In the study of the trend of dust storm index, the results showed that the study period of 2003-2007 in Semnan province has an increasing trend and has shown significant changes in the 95% confidence range, but the lack of significant changes in the last decade shows the effects of various events. In cross-cutting decisions in the field of dust in the region. The zoning of the DSI index changes in different regions of the province in a 15-year statistical period indicates that from the west to the east of the province due to the increase in the frequency of stormy days with moderate dust (MDS), dust has increased. The correlation between drought and DSI index in Semnan province showed that although DSI index increased during the period under analysis with increasing drought intensity and its correlation with drought during the 15-year period was not significant, but the pattern of DSI index is consistent with It is the pattern of the drought process. According to the results, it can be acknowledged that the dust situation has always been affected by climate, but the relationship between drought and the DSI index has always fluctuated with respect to droughts and wetlands. However, different climatic parameters are different and their impact is different. In addition to human activities, the main role of wind in the amount of dust or the existence of another source of dust should be considered.
Volume 10, Issue 2 (9-2023)
Dust storm is a complex process affected by the earth-atmophere system. The interaction between the earth and atmosphere is in the realm of the climatologists and meteorologists, who assess atmospheric and climatic changes, and monitor dust spread. Dust is the main type of aerosols which affects directly and indirectly radiation budget. In addition, altogether they affect the temperature change, cloud formation, convection, and precipitation. The most important studies about dust analysis have considered the use of remote sensing technique and global models for analyzing the behavior and dynamics of dust in recent two decades. To achieve such a goal, this paper has used MODIS and NDDI data to study and identify the behavior of atmospheric dust in half west of Iran.
Materials and methods
The western region of Iran is the study area. The data used in this study are divided into two categories: ground-based observations in 27 synoptic stations extracted from the Iran’s Meteorological Organization during the period (1998-2010) and satellite MODIS images during the first to fourth days of July 2008 as atmospheric dust extremes. Data was analyzed by using ArcGIS and ENVI software and NDDI index.
Results and Discussion
According to results, interpolated map for the number of dusty days during the study period over the western half of Iran showed that the scope of study area does not involve an equal system aspect quantity of occurrences. The number of dusty days occurrences increase from north toward south and the sites located in northern proportions of the area have experienced lower dust events. In contrast, maximum hotspots are occurring over southwestern sites such as: Ahvaz, Ilam, Boushehr and Shiraz. Therefore, principal offspring of dust input has been out of country boundaries and arrived at distant areas. Also, based on results obtained using satellite remote sensing images and applied NDDI index, maximum of intense dust cover is observed over Fars, Ilam, Boushehr and Ahvaz provinces on the first, second, third and fourth of July. However, the lowest rate of index situated in extent far such as: East and West Azerbaijan provinces. Thus, parts located on the north of the study area experienced less dusty days and the maximum dust cores were located in the southwestern (mostly Khuzestan). The long-term results were consistent with the daily average of NDDI index in the whole study area and indicated the hotspot areas (Ilam, Ahvaz, Omidyeh, Bushehr and Shiraz) during the first to fourth days of July 2008. However, the level of dust cover in the region has reduced when a wet and cloudy synoptic system passes over the central and northwestern parts of the study area.
Conclusions
The climatic interpolated map interpretation indicated that increase of dust concentration based on ground-based stations, which are consistent with dust concentration, is overshadowed by the latitude and proximity of sources of dust source in the Middle East. Also, the long-term climatic results of ground-based observations were consistent with the NDDI index calculated on dust extremes in the whole study area and in the southern areas (Ilam, Ahvaz, Omidyeh, Bushehr and Shiraz) during study days of July, 2008. Therefore, dust occurrence increases from north to south and the maximum hotspots over southwestern confirm the proximity of the south western region of Iran to deserts and sedimentary plains and their direct relationship with dust sources in the Middle East. These regions highlight the volume and expansion of dust outbreaks, which were well detected due to the satellite imagery and spectral characteristics of MODIS for monitoring changes in the dust phenomenon.
Overall, the use of satellite remotely sensed data/images not only cover the ground-based observation datasets gap to identify, highlight, and analyse the dust phenomenon, but also takes a much more geographical approach in analysing environmental hazards such as dust. It is also suitable for studies of atmospheric compounds such as atmospheric aerosols.
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