بررسي و شبيه‌سازي گردوغبار تابستاني در غرب و جنوب‌ غربي ايران

Study and simulation of summer dust in West and Southwest of Iran

يكي از مهم­ترين چالش­هاي زيست محيطي سال­هاي اخير در منطقه خاورميانه و ايران، پديده گردوغبار است كه عمدتاً در فصل تابستان رخ مي‌دهد. در اين مطالعه، ابتدا كد سينوپتيكي 06 روزهاي همراه با گردوغبار در بازه 5 ساله 2002 تا 2006 در 5 شهر غربي و جنوب‌غربي كه بيشترين خسارت ناشي ازپديده گردوغبار را متحمل مي‌شوند مورد بررسي قرار گرفت كه 80 روز مشترك همراه با گردوغبار به دست آمد. سپس با روش تحليل عاملي PCA، 2 خوشه غالب به دست آمد كه هر دوخوشه مبتني بر الگوي همديدي تابستاني گردوغبار بودند و در زمان وقوع اغلب توفانها در فصل تابستان بر منطقه حاكم است. پس از آن 4 توفان شديد و فراگير فصل تابستان در سالهاي 2005، 2008، 2009 و 2012بررسي شد كه در آنها بخش وسيعي از كشور ما تحت تأثير قرار گرفته است. 2 مورد از اين 4 توفان در خوشه اول و 2 مورد توفان گردوغبار ديگر در خوشه دوم قرار مي‌گيرند. بررسي‌هاي همديدي نشان مي‌دهد كه وجود گراديان فشاري شديد بر روي كشور عراق در خوشه اول و كشور سوريه در خوشه دوم، سبب وزش باد شديد در بيابانهاي واقع در اين كشورها و گسيل گردوغبار مي‌شود از طرف ديگر در سطوح بالا به دليل وجود يك ناوه عميق در منطقه در هر 2 خوشه، گردوغبار را تا ارتفاعات بالاتر جوي منتقل مي‌شود و توسط بادهاي غرب و شمال غربي به داخل ايران وارد مي‌شوند. مقادير مثبت تاوايي نسبي در اين دو كشور ، نشان‌دهنده وجود حركات صعودي در اين منطقه است. تصاوير ماهواره نيز چشمه گسيل گردوغبار را در شرق كشور سوريه براي خوشه دوم و بيابانهاي كشور عراق براي خوشه اول نشان مي‌دهند. خروجي مدل WRF-Chem براي غلظت ذرات گردوغبار نيز شروع گسيل از شرق سوريه در خوشه دوم يعني توفانهاي تابستان 2005 و 2009 و به تدريج انتقال آن به سمت غرب و جنوب‌غربي و نفوذ آن به مناطق مركزي ايران را به خوبي نشان مي‌دهد. همچنين در موردهاي 2008 و 2012 مرتبط با خوشه اول، مدل نشان مي‌دهد گردوغبار برخاسته از كشور عراق، به غرب و جنوب‌غربي ايران وارد مي‌شوند. مي توان نتيجه گرفت كه مدل WRF-Chem در هر 4 توفان، به خوبي چشمه گسيل، روند افزايش گردوغبار را نشان مي‌دهد اما روز حداكثر گردوغبار را با تفاوت يك روزه نشان مي‌دهد.

Today powerful dust storm destroys people lives and causes severe damages to their life and also causes financial problems in most regions of the world especially in west and southwest of Asia. Dust storm is one of the most important natural phenomena and also a kind of severe natural disaster that influence Iran and its west and southwest parts. The location of Iran on the desert belt is accompanied by frequent increasing of sand and dust storms. Integral prediction of dust storm phenomena can be useful in decreasing damages caused by these storms. So synoptic-dynamic analysis of dust storms and their simulation plays an important role in achieving to this goal. In this research, we investigate 4 severe dust storms in August 2005, September 2008, July 2009 and June 2012 that affected a large area of our country. select of dusty days were based on minimum visibility and maximum durability of that dust storm. At first, we show the minimum of daily visibility table. These data has been provided by Meteorological Organization in 5 western cities. The synoptic maps were related to these phenomena derived from NOAA website and synoptic and dynamic interpretation has been done. We have got the data with resolution of 2.5 degree from NOAA website. Then 700 hpa relative vorticity maps were drawn. We investigate MODIS images instrument on Aqua satellite and evaluate the amount of mass concentration of dust particles. Then the Lagrangian Integrated Trajectory Model has been used to determine the backward trajectory of dust particles. We run HYSPLIT model by GDAS data with a resolution of 0.5 degrees. At last we investigate the outputs of the WRE-CHEM model. This model was run to simulate dust storms by FNL data with a resolution 1 degree use for initial and boundary conditions. WRF-CHEM is used to simulate dust condition and transmission. As a part of WRF model, its main application is the study of atmosphere chemistry. At 500 hpa a very strong ridge entered Iran from the southwest. It covered all areas of our country which prevents the transference of dust to high levels of atmosphere. In 700 hpa relative vorticity maps show one day before dust storms reach to Iran a Positive voriticity is located in Iraq and Syria. So dust comes up to higher levels of the atmosphere and in dusty days in our country. There is a negative voriticity located in our country and because of downside movement of the air, dust storm happen in Iran. The time series of dust concentration of output models for Ahvaz are compared with the concentration data of Environmental Organization and visibility data. Results show that a low pressure system is located over the Oman sea that its blaze has been extended to the northwest of Iran. On the other hand a high pressure center is located in the Europe that extended to the east of Mediterranean. So strong pressure gradient were in Iraq and Syria and they caused the creation of strong winds in their deserts which caused dust emission. Satellite images showed that WRF/CHEM model is simulated very well in emission, source, diffusion and the extent of the areas covered with dust. Comparing PM10 concentration of the model outputs with Environment Organization data, show that WRF/CHEM model forecast daily changes well. But model underestimate significantly in quantity of concentration. These errors may be are due to a model considering only dust quantity but other pollutants affected on visibility. In general it can be said that in this event, dust concentration has been underestimated by WRF/CHEM model especially in maximum amount of PM10 concentration.