شناسایی و تحلیل الگوهای جوی مولد گردوغبارهای غرب ایران(مطالعه موردی: استان کرمانشاه) Journal Article

یکی از مشکلات زیست‌محیطی کشور ما، وقوع رخداد طوفان‌‌های گردوغبار به‌ویژه در استان‌‌های غربی و جنوب‌‌غربی کشور است؛ از این رو، در این پژوهش به بررسی و تحلیل سینوپتیکی چگونگی شکل‌‌گیری پدیده گردوغبار، شناخت مناطق منشأ و مسیر ورود آنها به نیمه غربی ایران (مطالعه موردی: استان کرمانشاه) پرداخته شده‌‌است. پس از استخراج روزهای گردوغباری، داده‌های تراز دریا، 700، 850 و 500 هکتوپاسکال به همراه تاوایی متناظر با روزهای گردوغبار با استفاده از امکانات برنامه‌نویسی در محیط گردس استخراج شد. سپس به کمک تحلیل خوشه‌ای، روزهای نماینده و الگوهای گردوغباری غرب ایران در محیط متلب شناسایی شد. نتایج نشان داد که رخداد گردوغبارهای استان کرمانشاه تحت‌‌تأثیر پنج الگوی جوی مختلف است که بیشترین فراوانی به الگوی اول و دوم بازمی‌گردد که کم‌فشار موسمی هند کنترل‌‌کننده اصلی آن است؛ با این حال، شدیدترین رخدادهای گردوغباری کرمانشاه زمانی ایجاد می‌شود که گردش موسمی هند در جنوب و جنوب‌‌شرق آسیا، جریان مداری غرب‌سو و مداومی در تراز زیرین جو ایجاد کند که محل اصلی همگرایی و نزول آن، چاهه گرمایی جنوب غرب آسیا تا شرق مدیترانه است؛ به‌‌طوری که هسته پر ارتفاع آزور در تراز 500 هکتوپاسکال، با ایجاد همگرایی فوقانی و نزول قائم هوا به تشدید و تقویت کم‌فشار سطحی منجر می‌شود. علاوه بر این، کم‌فشار حرارتی سودان و دریای سرخ با تغییر حالت از ترمودینامیکی به دینامیکی به همراه سامانه‌‌های پرفشار اروپا، حداکثر میزان شیو فشاری را در نواحی خشک و بیابانی عربستان، عراق و شمال آفریقا ایجاد می‌کند؛ به‌گونه‌ای که کشیده شدن ناپایداری تا تراز 700 هکتوپاسکال و استقرار ناوه مدیترانه‌ای، به تداوم و ماندگاری بیشتر روزهای گردوغباری منجر می‌‌شود. این شرایط همراه با شرایط دیگر نظیر خشکی شدید هوا، به برخاستن گردوغبار از نواحی بیابانی عربستان، عراق، سوریه و شمال آفریقا و انتقال آن به نواحی غربی ایران منجر می‌‌شود.

1- Introduction In the last decade, the volatile region of the Middle East, along with all other natural hazards, has been plagued by dust storms. More than anywhere else in the world, global warming and climate change have affected the natural ecosystems of this vulnerable and fragile region. From a synoptic meteorological point of view, storm is a unique destructive phenomenon on synoptic maps that includes a combination of pressure, cloud, rain, wind, et.c (Alijani, 2006; Hosseini, 2000). Dust can be a reaction to changes in land vegetation, according to which the role of human activities along with the natural conditions of geographical environments should be considered (Arimoto, 2000). Burial of residential areas under sand, destruction of agricultural lands and expansion of desert areas (Wang 2005), creation of colored rainfall, disruption of transportation system, disruption of agricultural fields and orchards (Koren et al., 2015), air pollution, respiratory problems and diseases, and the prevalence of infectious diseases are the most important complications and problems caused by dust storms (Goudie and Midelton, 2002). Therefore, it is necessary to identify and analyze dust-generating patterns of prognostic aspects. 2- Methodology In this research, the synoptic analysis of dust in Kermanshah province has been studied. For this purpose, dust codes for 12 synoptic stations over a period of 30 years (from 1990 to 2017) were received from the Iranian Meteorological Organization. Then, in order to perform the classification operation and further calculations, sea level pressure (SLP) and geopotential height of 500 hPa level data were extracted for grading days by programming in GrADS software. In the next step, in order to classify sea level pressure data and identify representative days, cluster analysis was performed on dusty days and dust generating atmospheric patterns were extracted, and finally the synoptic and dynamic analysess and interpretation of these patterns were performed .3- Results By performing cluster analysis on sea level pressure events, five patterns for dust occurrence in the western region of Iran can be identified as follows: Pattern1: Indian monsoon low pressure - European migratory high pressure: A study of this model shows that all regions located in southwest Asia to the center of the Mediterranean have become the convergence of currents originating from the monsoon region of South and Southeast Asia. Summer monsoon rotation, the region of South-Southeast Asia, has acted as a large-scale energy source. The regions located in Southwest Asia and the Eastern Mediterranean are the main area of ​​convergence of this flow and, in fact ,are heat wells. Pattern2: Indian monsoon low pressure integration, Oman Sea - North Caspian high pressure: Like the first pattern, Indian monsoon low pressure system is formed on the northwestern regions of India and on the border with Pakistan, which moves in orbit through the Oman Sea and the Persian Gulf. It has entered the regions of Southwest Asia and covers a large area from the Middle East to North Africa, and has strengthened its coverage of the central to eastern Mediterranean. Pattern3: Sudan low pressure, European low pressure - North African high pressure: A study of this model shows that at sea level, the Sudanese low pressure system travels from the southern and central parts of the Red Sea to cyclonic and meridional directions. The interior region of Saudi Arabia and the desert of Ruba'at al-Khali have moved and covered all the desert areas of Saudi Arabia, Iraq and Syria in such a way that it has caused the bottom convergence and vertical ascent of the currents over the dust centers. In addition, in the orbital direction and in the vicinity of this system in North Africa (Libya, Egypt and Algeria), a high-pressure system with a central pressure of 1016 hPa prevails, which leads to severe pressure differences and increased instability in dust centers and over-activation. It has resulted in dust hotspots in Saudi Arabia and North Africa. Pattern4: Sudan low-pressure integration Sudan, Saudi Arabia - Siberian high-pressure: Sudan-origin low-pressure system with high spatial and spatial expansion across the Red Sea is integrated with Saudi low-pressure on one side and on the other; moving northwards with expanded tabs and Indian influence in the eastern and southern parts of Iran has created a huge expanded belt of low pressure centers. In addition, a weak high-pressure system with a central pressure of 1016 hPa over the Mediterranean Sea and North Africa has created atmospheric instability due to the pressure difference created over desert areas.These areas are the focal points of dust and the main generator of dust storms in the Middle East. Pattern5: Polar low pressure, Sudan low pressure - European high pressure: A study of this model shows that the polar low pressure system along with Sudan and Red Sea penetration low pressure are the main controllers of Iran's atmosphere at sea level in such a way that the cyclonic movement of cold currents in the polar regions towards the lower latitudes and its penetration from the northeast into Iran and then the integration of its tabs with the low pressure tabs of the Red Sea and Sudan cause the corridor to have unstable currents in the polar and tropical regions, or in other words, the polar and subtropical regions, which have dominated the upward vertical currents in a very large area of ​​Iran. However, the dominance of the European high pressure system and its penetration to eastern Turkey in the orbital direction and North Africa in the meridional direction and its confrontation with the infiltration low pressure cause severe compression pattern, instability and transport of dust into the low pressure Sudan and the Red Sea. 4- Discussion & Conclusions Studying and understanding the synoptic and dynamic state of the atmosphere as well as understanding the local conditions and geomorphology of each region is one of the key topics of interest in atmospheric studies. Dust storms in the western part of Iran are mainly caused by certain weather conditions. Thus, the components of the atmospheric circulation scale at the lower levels play a major role in the occurrence of dust storms. In the patterns of the warm periods of the year, the dominance of the west current with the monsoon origin of India has created the following convergence around the dust centers of southwest and west Asia, which are intensified by the upper convergence caused by the high pressure of the Azores or the western wave. This issue is accompanied by the activation and rising of dust in the dust centers of the region, which eventually extends to the western region of Iran by eastward and orbital currents. On dusty days occuring in the cold seasons, Sudan and Red Sea thermal low pressures on Saudi Arabia, Iraq and Syria at sea level, and low-lying nuclei and western waves on Europe and the Mediterranean Sea at mid-atmospheric level are the main controllers of climatic conditions in the region. Therefore, in the cold period of the year, due to the heaviness of the cold weather in these days, they are allowed to penetrate to low offerings and place the eastern part of trough on the deserts of North Africa, Saudi Arabia, Iraq and Syria. By creating instability and moving to the east, they direct the generated dust to the west of Iran. However, whenever tabs of Indian monsoon low pressure and Sudan low pressure enter the West Asian region at sea level and the Mediterranean subtropical or high-pressure submarine operates in mid-atmosphere, the upper convergence and the dynamic decrease of air flow causes the amplification and over-activity of surface low pressures, which is accompanied by the activation of dust centers and the rise of dust in the area. In general, Azores high pressure along with migratory systems of western winds is the most important synoptic factor in dust systems in the western regions of Iran. Comparison of research findings showed that thermodynamic processes in the hot season and dynamic processes in the cold season are the most important factors in the formation and transfer of dust to the western half of the country (Kermanshah). Thus, the establishment of low thermal pressure at ground level and low altitude of 850 to 500 hPa in the vicinity of western Iran is effective in generating identified dust during the warm periods of the year, which is consistent with the findings of Azizi et al (2012) in the synoptic study of dust in the western part of the country.