جستجوی مقالات مرتبط با کلیدواژه "storm" در نشریات گروه "محیط زیست"

One of the environmental problems in recent years in the western regions of Iran is the activity of dust storms and aerosols in the atmosphere of cities. Malayer, Nahavand and Tuyserkan cities in the south of Hamedan province and west of Iran are vulnerable to the entry of dust storms. In this research, dust storms, aerosols and visibility status and the manner of entering these storms into the cities have been studied.
In this study, different statistical periods were studied for three cities during the years 1992 to 2010. Then, the Prevailing wind conditions, storms dispersion, and visibility reduction were studied throughout the year. Also, maps of pressure patterns on the days of the storm for synoptic analysis were prepared and evaluated.
Findings: The maximum annual dust incidence has occurred in Malayer in mid- spring (May), in Nahavand in the early spring (April) and mid-summer (August) and also in Tuyserkan at the end of spring (June).The highest and lowest number of dust storms occurred in Tuyserkan and Nahavand, respectively. Periodic changes of dust in the region have identified the rise of this climatic phenomenon in recent years. Dust frequency changes have shown a positive trend in the region with increasing height.The number of days with low visibility corresponded to the months of the occurrence of dust storms in the region and the most number of days with low visibility have been in June and July. Moreover, the synoptic analysis of the atmosphere shows that during the storm, an intense gradient of pressure and instability near the surface of the earth and the convergence flow at the level of 500 hPa have been created on the region.
Discussion and Counclusion: The results of this study indicate that the dust in the streets parallel with the Prevailing wind direction is easily transmitted to the central parts of the city. Then due to the collision of the dust stream with the city's high buildings, a part of the dust is transferred to the surface of the earth, and other part of the flow creates a torsion mode in the back section of the building. Eventually, another part of it passes through the city at altitudes above the buildings. Vegetation around the cities has reduced the flow of dust into the cities and is considered as a positive factor in reducing pollution in the region.