تحلیل همدید روزهای گردوغباری شدید دورۀ گرم در مناطق مجاور پهنه‌های بیابانی (مطالعۀ موردی: اهواز)

هدف این پژوهش کشف رابطۀ میان الگوهای گردشی پدیدآورندۀ گردوغبارهای شدید اهواز با رویکرد محیطی به گردشی است. بدین منظور، داده‌های شبکه‌ای روزانه ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال، فشار تراز دریا و مولفه‌های باد مداری و نصف‌النهاری به‌صورت متناظر با 229 روز گردوغباری شدید دورۀ گرم از پایگاه داده (ncep/ncar) دریافت شد. با انجام تحلیل خوشه‌ای پایگانی انباشتی بر روی نقشه‌های ارتفاع ژئوپتانسیل و فشار تراز دریا با آرایه‌ای به ابعاد 1617 ×229 و ادغام روزها به روش وارد 3 الگوی گردشی برای تراز 500 هکتوپاسکال و 3 الگوی گردشی برای فشار تراز دریا شناسایی و برای هر الگو، یک روز به‌عنوان نماینده بر اساس ضریب همبستگی با آستانۀ 95% تعیین و نقشه‌های ترکیبی فشار تراز دریا و الگوهای ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال، بردارهای سرعت و جریان‌های هوا در این روزها ترسیم و تحلیل شد. نتایج این پژوهش نشان می‌دهد که بر اساس الگوهای 1 و 2 در ترازهای 500 هکتوپاسکال و فشار تراز دریا رخداد گردوغبارهای شدید اهواز متاثر از استقرار فرودی در شرق مدیترانه و کم‌فشارهای حرارتی سطح زمین به‌ویژه کم‌فشار خلیج فارس است. در الگوی 3 دو تراز مزبور نیز همگرایی مداری سامانۀ چرخندی خلیج فارس و پرفشار آزور و در نتیجه افزایش شیو فشار روی منطقه موجب انتشار و انتقال پدیدۀ گردوغبار در خوزستان و شهر اهواز می‌شود. بر اساس این پژوهش، مهم‌ترین منابع گسترش گردوغبار به قلمرو مطالعاتی بیابان‌های عراق، عربستان و سوریه است.

Synoptic Analysis of the Effects of Severe Dust Days of a Warm Period on Deserts' Adjacent Regions: A Case Study of Ahwaz City

Introduction: increasing dusty storms has been one of the most important consequences of climate change in recent years that directly or indirectly affected human society. Countries located in the arid and semiarid regions of the world, including Iran, have been affected more than other parts of the globe by this natural disaster and its harmful consequences, especially the atmospheric dust, which could bring about a wide variety of detrimental effects such as the reduction in growth and yield of crops, the occurrence of plant plagues and diseases, an increase in road accidents due to the decrease in the vision field, cancellation of flights, and rising health costs. These facts, along with repeated droughts in recent years and the potential consequences of climate change as a result of desertification, have brought the issue of dust storms and their relevant side effects, including increasing respiratory and pulmonary diseases, a disorder in the ground and air transportation, environmental destruction, and pollution of agricultural products to the attention of many researchers. Therefore, numerous researches have been carried out on the increase of global and regional dust and the identification and analysis of dustgenerating regionschr('39') circulation patterns. These include Romanof (1951), Goudie and Midelton (2001), Kutiel (2003), Barkan et al. (2005), Dayan et al. (2008), Barkan (2008), Calastrini et al. (2012), Awad and Mashat (2014), Kang et al. (2016), Beegum et al. (2018), Hemmati( 1995), Dehghanpour (2005), Zoualfaghari and Abedzadeh (2006), Heidari (2007), Raeispour (2008), Karami (2009), Tavousi et al. (2011), Movahedi et al. (2012) Tavousi and Zahraei (2013), Zangeneh (2014), Khorshiddoust, et al. (2014), Omidvar and Sepandar (2018) to mention a few. Materials and methods: as located near deserts, Ahwaz city is directly exposed to dusty storms. This study, therefore, set out to investigate the relationship between circulation patterns that cause severe specks of dust in Ahwaz and the environmentcirculation approach. To this end, the required data were collected from the environmental database of 390 sever dusty days of the region during 14 years (20012014), and the severity of dusty days was determined according to the allowance limit index AQI (150 mu;g/m3) for two cold (161 days) and hot (229 days) periods. The data were then evaluated based on the frequency of severe dusty days throughout the hot period. For this reason, daily network data regarding the geopotential height in 500 hPa, sea level pressure, and the zonal and meridional wind were obtained from the database (NCEP/NCAR). Conducting an accumulation hierarchical cluster analysis for sea level pressure and geopotential height map with matrix in 229 ×1617 dimension and linkage days using Ward method, three circulation patterns were identified for level 500 hPa, and three circulation patterns were found for sea level pressure. Moreover, for every pattern, one day has been determined as an indicator based on the correlation coefficient of 95% threshold, and the composite maps of sea level pressure and height patterns of geopotential in level 500 hPa, the speed vectors, and streamlines in these days have been drawn and analyzed. Results Discussion: The results of the study indicated that according to patterns 1 and 2 in level 500 hPa and at sea level pressure, severe dusty storms in Ahwaz were influenced by the eastern Mediterranean currents and low thermal pressures of the earth surface, especially the Persian Gulf low pressure. In pattern 3, the two levels mentioned above, cyclonic system zonal convergence of the Persian Gulf, Azores high pressure, and enhancement of gradient pressure on the region, resulted in the distribution and transfer of the dust phenomenon in Khuzestan province and Ahwaz city. Conclusion: According to the findings of this study, the most important sources of dust distribution in the study area are the deserts of Iraq, Saudi Arabia, and Syria. This studychr('39')s results could be useful for preventing and controlling dust storms via the identification of dustgenerating regions. To reduce the damages caused by the study regionchr('39')s dust phenomenon, an international agreement with the adjacent countries needs to be made. Moreover, the issue requires interorganizational cooperation of relevant entities at the domestic scale.