عنوان مقاله [English]
Dust phenomenon is one of the most harmful natural disasters in low rainfall regions of the world, especially in Iran, which brings many environmental problems in these areas. It is also one of the environmental challenges in the Middle East and Iran in recent years. This phenomenon has become one of the main problems in arid and semi-arid regions today, which has adverse social, economic and environmental effects and it can be said with certainty that one of the environmental hazards in arid and semi-arid regions of the world are dust storms, This environmental event is considered as a climatic hazard and causes or exacerbates cardiovascular diseases, respiratory diseases and many allergies in the human body, Large amounts of dust are transported every year from the deserts of North Africa, the Arabian Peninsula, Iraq and Syria to different parts of Iran. Depending on global warming and wind speeds such as Harmatan and other strong local winds, these dusts are drawn to an altitude of 3,000 meters and above and are transferred to the areas in front of these systems by entering the wind systems of the Mediterranean and North Africa. Dust is one of the most common atmospheric phenomena and one of the biggest environmental problems in arid and semi-arid regions, which has devastating effects on the inhabitants of these areas every year. In recent years, pollution caused by dust particles has become one of the environmental problems, especially in developing countries. Considering that Iran is also located in the arid and semi-arid region of the world and a large area of the country is considered as an arid and semi-arid region, it is necessary to study this phenomenon.
The main purpose of this study is to explain the causes of occurrence and routing of dust storm springs in Kermanshah in the three-day period from October 26 to 28, 2018. In the first stage, using meteorological data, the days associated with the dust storm were determined. In the second stage, for synoptic analysis of the causes of the storm, from the ECMWF European Center for Medium-Term Forecasting Database with a resolution of 0.125 degrees, including geopotential height of 500 hPa, omega of 700 hp, sea level pressure SLP, components Orbital and meridional wind at the level of 300 hPa, special humidity at the level of 700 hPa due to higher resolution and satellite data of soil moisture to a depth of 10 cm were used in the study area. Using the above data in using GRADS software; Wind patterns and synoptic systems effective in transporting fine dust to Kermanshah were drawn. In the third stage, using the HYSPLIT model, dust particles were detected at three levels of 200, 1000 and 1500 meters above the ground at a time interval of 6 to 48 hours before the occurrence of dust. WRF-CHEM numerical weather simulation model was used to prepare numerical maps of particle concentration distribution and dust storm path to western Iran. In the present study, using version 3,6,1 of the WRF-CHEM paired model, simulations were performed for 3 days from 26 to 28 October 2018 using GFS analysis data for initial and boundary conditions. In this implementation, the advanced MADE-SORGAM schema was used as the emission pattern of airborne particles, which in turn is based on the regional model of airborne particles. In MADE design, airborne particles in three models with a diameter of less than 0.1 μm, cumulative with a diameter between 0.1 to 2 μm and large with a diameter greater than 2 μm with a log-normal distribution were included in the air quality simulation process. In the last step, MODIS images were used to determine the sources of dust diffusion to the west of Iran, and also by using the optical depth detection index of AOD aerosol, the numerical distribution map of dust aerosols in the atmosphere was obtained.
According to the results of the analysis of synoptic maps, in fact, the main cause of the dust wave phenomenon from 26 to 28 October 2018 in Kermanshah, in addition to the instability caused by low surface heat pressures, Saudi high-pressure movements that cause currents to converge towards Have become western. Deployment of a low pressure section in the middle levels of the atmosphere is well visible in this event, so that despite the instability in the middle level of the atmosphere, lack of sufficient moisture in the systems transferred to the west of the country, currents flowing through the deserts of Iraq and Syria. Sufficient both in the surface and in the depth of the soil inside the country and in neighboring countries has led to the formation of a dust spring and its transfer to the study area. Also, the examination of the tracking maps obtained from HYSPLIT shows that two general paths for the transfer of dust to the study area can be identified: 1- The northwest-southeast route, which passes through dust cores formed in the deserts of Iraq and Syria, transports dust to the western half of Iran; This route can be considered as the entry of dust into the area at an altitude of 1000 to 1500 meters. 2- The southwest-west route of Iran and the city of Kermanshah, which at an altitude of 200 to 1000 meters, which is the main source of dust on October 27 and 28, is the source of particles in this route Kuwait, northern Saudi Arabia and part of Iraq. Examination of the particle path shows that these particles were first transported to higher levels by low pressure systems located in the area and then pulled to the ground in two paths. The soil moisture map also shows a severe lack of moisture up to a depth of 10 cm in the soil that at the same time with the passage of unstable systems and western currents over the areas, subsoil particles are easily separated from the ground and transferred to the study area. By simulating dust storms from the west wind by the WRF-chem model, it showed that the main source of dust is located in the western and central deserts of Iraq, Syria and northern Saudi Arabia.