تحليل همديدي و ديناميكي پديده گرد و غبار و شبيه سازي آن در جنوب غرب ايران در تابستان 1384

Synoptic-dynamic analysis of dust storm and its simulation in southwest of Iran in summer 2005

يكي از مشكلات زيست محيطي كشور ما وقوع رخداد توفانهاي گرد و غبار به ويژه در استانهاي غربي و جنوب غرب كشور است. در اين مطالعه، به بررسي توفان شديد و فراگير مرداد ماه 1384 مي پردازيم كه در آن بخش وسيعي از كشور تحت تأثير اين توفان قرار گرفت. ملاك انتخاب روزهاي گرد و غباري شاخص، گزارش گرد و غبار در اكثر ايستگاهها، حداقل ديد و حداكثر تداوم مي­باشد. ابتدا جدول حداقل ديد افقي روزانه با كمك داده هاي سازمان هواشناسي در 5 شهر غربي كشور ارائه مي‌شود. سپس نقشه‌هاي همديدي مربوط به اين پديده از وبگاه NOAA استخراج مي‌شود و تفسير همديدي و ديناميكي آنها انجام مي شود. سپس تصاوير سنجده MODIS ماهواره Aqua و ميانگين غلظت جرمي ذرات گردوغبار اين سنجنده در پديده مورد نظر مورد بررسي قرار مي‌گيرد. سپس با كمك مدل لاگرانژي HYSPLIT مسير ذرات گردوغبار رديابي مي‌شوند. پس از مسيريابي پس گرد ذرات گردوغبار، مناطق بياباني كشور سوريه بعنوان كانون شكل گيري گردوغبار شناسايي شدند. در آخر، خروجي‌هاي غلظت گردوغبار مدل WRF-Chem مورد بررسي قرار مي‌گيرد. به منظور صحت سنجي، خروجيهاي مدل در شهر تبريز اين خروجيها با داده‌هاي غلظت سازمان محيط زيست و داده‌هاي ديد افقي سازمان هواشناسي كشور مقايسه مي‌شود. نتايج خروجيهاي مدل به خوبي روند افزايش گردوغبار و روز حداكثر گردوغبار را نشان مي‌دهد، اما اين خروجيهاي غلظت گردوغبار تفاوت چشمگيري با مقادير واقعي دارد.

Dust particles consist of important aerosols and resulting in blowing strong winds on the surface of desert areas. These particles enter the atmosphere under the influence of different factors including: weather condition (wind, precipitation and temperature), land surface (topography, humidity level, roughness and vegetation), soil features (texture, density, composition and land use (agriculture). 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 part. The location of Iran on the desert belt is accompanied by frequent increasing of sand and dust storm. 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 play an important role in achieving to this goal. In this research, we investigate severe dust storm in August 2005 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 output of the WRE-CHEM model. This model was run to simulate dust storms in 7-10 August and 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 storm 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. Dust loading and friction velocity of outputs of the model has been drawn in dusty days. The time series of dust concentration of output models for Tabriz are compared with the concentration data of Environmental Organization of visibility data. Result 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. Friction velocity related to the model outputs show that the velocity of wind is high in dusty days in Iraq and Syria. So conditions are suitable for dust raining. 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 MP10 concentration of the model output with and Environment Organization data of Tabriz city show that WRF/CHEM model forecast daily changes well. But model underestimate significantly in quantity of concentration. This error may be 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.