تحلیل و ردیابی مسیرهای ورود توفان‌های گرد و غبار به شرق ایران با استفاده از مدل پخش لاگرانژی ذرات Hysplit

امروزه معضل توفان های گرد و خاک به بحرانی منطقه ای و جهانی تبدیل شده است. پژوهش حاضر بر آن است که با استفاده از مدل عددی، تصاویر ماهواره ی modis و شاخص aod و نقشه های همدیدی، به تعیین منابع گرد و غبار و چگونگی حرکت آنها بر فراز نیمه ی شرقی ایران طی فصل گرم سال بپردازد. در مرحله ی اول با استفاده از داده های مشاهداتی، تصاویر ماهواره و شاخص عمق اپتیکی گرد و غبار، توفان های گرد و غبار فصل گرم طی دوره ی آماری 2010 تا 2018 مشخص شد. سپس به بررسی عوامل همدیدی موثر بر رخداد این پدیده پرداخته شد؛ برای این امر با مراجعه به تارنمای مرکز اروپایی، پیش‌بینی میان‌مقیاس جوّی (ecmwf) داده های دما، فشار تراز دریا (slp)، مولفه‌های مداری و نصف‌النهاری باد، ارتفاع ژئوپتانسیل در ترازهای 850، 500 و250 هکتوپاسکال با دقت فضایی 0.25 * 0.25 درجه دریافت شد. در مرحله ی بعد برای منشایابی این توفان ها، از مدل پخش لاگرانژیhysplit به روش پسگرد استفاده شد. نتایج حاصل از مطالعات همدید نشان داد زمانی که یک سلول مستقل پرفشار بر شمال شرق افغانستان و شمال شرق ایران، همچنین سلول کم فشار بسته ای بر جنوب غرب افغانستان وجود دارد، گرادیان شدیدی بین این مناطق ایجاد و باعث می شود سرعت باد در سطح زمین به بیش از 14 متر بر ثانیه برسد. اختلاف شدید فشاری و دمایی در منطقه، نبود رطوبت و زاویه ی تابش بالا سبب می شود گرد و غبار بیابان های خارج از مرزهای شمالی و شرقی به منطقه هدایت شود. همچنین در این فصل، منطقه تحت تسلط پر فشار جنب حاره آزور قرار دارد که بلوکه شدن آن در سطوح بالا به تداوم گرد و غبار در شرق ایران به مدت سه روز منجر شده است. خروجی های مدل و تصاویر ماهواره نشان داد که به طور کلی بیش از 90 درصد منابع اصلی غبار برای توفان های گرد و غباری شرق ایران، محدوده ای در حد فاصل بیابان های مرکزی ترکمنستان، قزاقستان، افغانستان و دشت سیستان است.

Analysis and tracking dust storms routes entering to east of Iran using the particle diffusion HYSPLIT model

Extended abstract1 IntroductionA dust storm is one of the biggest serious environmental problems in the arid and semiarid regions of the world, causing irreparable damages to farms, facilities, roads, traffic and transportation every year and respitory problems by contaminating the air. Due to the geographic location of Iran which is in the arid and semiarid belt of the world, the country is frequently exposed to local and synoptic dust systems. Considering the increasing occurrence of dust in the coming years, drought and climate changes and the emergence of desert zones, the study of this phenomenon is considered important and should be studied by using scientific researches to identify the factors affecting the occurrence of this phenomenon and dust source areas. The main purpose of this research is to identify the sources and also track the dust route entering the east of Iran using the HYSPLIT model, satellite images and synoptic analysis.2 MethodologyIn this study, At first, warm season dust storms were studied by using weather data, phenomenal code and horizontal visibility. Then, the storm from August 12 to 14, 2018, was recorded using weather data for East stations and horizontal visibility. For more accuracy, MODIS images of the storm wave on this day were identified and the surface dust concentration was confirmed using the AOD Index. Then, using the European Center for Average Meteorological Data (ECMWF) with a spatial resolution of 0.25 * 0.25, sea level pressure (SLP), temperature, direction and wind speed, and geopotential height At 850, 500 and 250 levels, jet streams were investigated and The synoptic factor of the dust storm was determined. In the next step, using the HYSPLIT model, the path of motion of particles and their source were determined at three levels of 500, 1000 and 1500 meters for 24 hours before the storm. The meteorological data of the model was obtained from a 0.5 degreess GDAS.3 Results The intensity and extent of the dust storm from August 12 to 14, 2018 showed that its horizontal visibility had been decreased to less than 200 meters across stations in eastern half areas of Iran. On this day, the dry bed of Hamoun, Pozak, Saberi and Hirmand, Afghanistan's plains have been contributed to nourish the storm. The results of synoptic studies showed that when there is a high pressure independent cell in the northeast of Afghanistan and northeast of Iran as well as a lowpressure cell in the southwestern part of Afghanistan, a severe gradient is made between these regions that causes the wind speed at ground level to be more than 14 meters per second. The severe pressure and temperature differences in the region, the lack of humidity and the high radiation angle have drove the dust of deserts outside the northern and eastern borders toward the region, and this area has been under the Azores subtropical high pressure, which its blockage at high levels leads the persistence of dust for three days in eastern Iran. The results of the model also showed that more than 90% of the dust entry routes to the east enters the eastern part of Iran from the deserts of Turkmenistan, Khazakhistan and Afghanistan.4 Discussion ConclusionsDue to 120day winds, low humidity, poor vegetation and dry regional substrates, the eastern part of Iran is prone to the frequent occurrence of dusty phenomena. Based on satellite images and AOD index, the storm has formed in the desert region of Turkmenistan and has been expanding to eastern Iran. According to the synoptic study of the warm period of the dust storm in the east, the upper levels of the Iranian plateau are under the control of the Azores high pressure and on the ground surface, the thermal low is also increasing in the eastern half. When two strong lowpressure nuclei with a 990 hp center in southeastern Afghanistan and southeastern Pakistan were deployed so that its tabs penetrated into the studied region and progressed to the Mediterranean, it created the appropriate conditions for climbing a huge amount of dust into the air that in the case of dryness of the area and northnorthwestern and northeastern flow of the upper levels, this phenomenon intensified and moved to the eastern part of Iran. At high atmospheric levels, due to air stability and blocking events, as well as air stagnation, the dust is more durable temporally and the process of bringing it down to the ground surface will last longer days. The results of the HYSPLITE modeling output also showed that the source of dust of the eastern half of Iran in the storm studied enter the studied area from the deserts of Turkmenistan and northwest of Afghanistan and Khazakhistan with the north, northwest and northeastern directions up to 90 percent. In all cases, the results of the model are compared with and confirmed by satellite and synoptic studies.