منشايابي توفان‌هاي گردوغبار در جنوب غرب ايران با استفاده از تصاوير ماهواره‌اي و نقشه‌هاي هوا

Sources of Dust Storms in South West Iran Using Satellite Images and Weather Maps

هدف از اين پژوهش شناسايي الگوهاي سينوپتيكي موثر در ايجاد توفان‌هاي گردوغبار و تشخيص مناطق خيزش اين توفان‌ها در جنوب‌غرب ايران است. روش پژوهش، تحليل سينوپتيكي همراه با پردازش تصاوير ماهواره‌اي است. داده‌هاي روزانه گردوغبار در سيزده ايستگاه سينوپتيك براي دوره 1990-2012 استخراج شد. سپس، دو موج شاخص كه بالاترين شدت و وسعت را داشت، انتخاب و بررسي شد. نقشه‌هاي هوا از سايتNCEP/NCAR و تصاوير ماهواره‌اي NOAA/AVHRR از سايت NOAA/CLASS دانلود و به‌كار گرفته شد. تحليل الگوهاي فشار براي توفان اول نشان داد اختلاف ارتفاع بين پرارتفاع شمال آفريقا و كم‌ارتفاع روي ايران در تراز850 موجب شكل‌گيري كم‌فشار قوي در سطح دريا در منطقه مورد مطالعه شد. اين كم‌فشار قوي با قدرت مكش بسيار بالا هواي گردوغباري بيابان‌هاي اطراف را به منطقه مورد بررسي مكش كرد. در مورد دوم نيز اختلاف فشار بين دو سيستم پرارتفاع روي عربستان و خليج‌فارس و كم‌ارتفاع روي مديترانه در تراز 850 سبب وزش باد از مناطق بياباني اطراف به منطقه مورد بررسي شد. نقشه سطح زمين اين توفان نيز نشان داد كم‌فشار سودان بادهاي گرم و خشك و آلوده به ذرات گردوغبار عربستان را به منطقه ما وارد مي‌كند. پردازش تصاوير ماهواره‌اي نيز اين نتايج را تاييد كرد.

Introduction The dust storms are one of the climatic hazards in the dry climates of the world. They cause many damages to the environment and humans. One of the aspects of a study to understand the origin of this phenomenon is the formation of foci in the recent years in the areas of research. It has been done in the central regions. The dust storms have gained global scale. This has demonstrated that the primacy of the Sahara has highlighted the importance of some other drylands, including the Middle East, Taklamakan, southwest Asia, central Australia, the Etosha and Mkgadikgadi pans of southern Africa, the Salar de Uyuni of Bolivia and the Great Basin in the USA). The Asiaan dust storms are most frequently originated from Taklamakan Desert of China and the Gobi Desert of Mongolia and their peak is in late winter and early spring. West and southwest part of the Iranian dust are from a local cell. Due to its geographical location in the arid climates of the world, Iran experiences these storms every year; especially in the southwest. That is why this study was undertaken to identify the sources and tracks of these storms in the south west of the country. Dust storms in Khuzestan are likely emerged from sandy deserts, dried lakebeds, or chemically- and naturally-polluted regions in neighboring countries. They are borne upwards and carried by winds to Iran. Those airborne dusts in Khuzestan come from the same source, where is likely an eroded sedimentary environment outside Iran. In general, airborne dusts in Khuzestan are geochemically similar to airborne dusts. Materials and Methods Due to its geographical location in the arid climates of the world, Iran experiences these storms every year; especially in the southwest. That is why this study was undertaken to identify the source and tracks of these storms in the south west of the country. For this purpose the daily dust data of 12 meteorological stations in the study area were extracted for the 1990-2012 period. Then, two significant waves were selected in the region of the highest intensity. The synoptic method (to detect other patterns and to create effectively two dust storms) and remote sensing technology (to identify the source regions of dust storms) were studied as a common method for the research. Their source region was determined through the use of NOAA/AVHRR images and their tracks were identified over the synoptic weather maps of the two widespread and intensive storms. The weather maps were obtained from the NCEP/NCAR site. Results and Discussion The map of a low voltage 850 hPa in the study area is based on the high altitude and low altitude in northern Africa. This low-voltage high-power suction air could produce dusts in the vicinity of desert region of Saudi Arabia, especially in the desert sucks. Check maps for pressure waves of dust in 2012 showed the pressure difference between the two systems on high altitude and low altitude in Arabia and the Persian Gulf in the Mediterranean winds of 850 hp near the desert region. The storm also showed a map of the surface low pressure with hot dry winds from Arabia Sudan that is contaminated with dust particles to enter the area. The dust rising and dust particles are studied by processing the satellite imagery (SST NDVI) of the Arabian Peninsula (Rub al Khali) and Oman. According to the South East Arabian and Oman, most of the areas of the region are rising and shifting dust particles. Conclusion The results indicated that the frequency of dust storms has increased during the study period. It can be concluded that spatial distribution of the dust storms have been increased from north to south. The synoptic system responsible for the development of the two selected storms was a low pressure over the study period. This system caused the inflow of the dust from the deserts of Arabian Peninsula to the study region. The analysis of the satellite images confirmed this finding.