مدل‌سازی عددی خواص فیزیکی، جریان‌ها و پیچک‌های دریای خزر جنوبی

نوع مقاله : مقاله پژوهشی‌

نویسندگان

1 دانش‌آموخته کارشناسی ارشد، موسسه ژئوفیزیک دانشگاه تهران، تهران، ایران

2 دانش آموخته دکتری، مرکز علوم جوی و اقیانوسی سازمان هواشناسی، تهران، ایران

چکیده

پژوهش حاضر به مطالعه تغییرات فصلی فرایندهای فیزیکی خزر جنوبی با استفاده از مدل اقیانوسی ROMS می‌پردازد. این مدل عددی برای هفت سال اجرا شد و خروجی‌های آن در سال آخر (2018) برای این پژوهش به‌کاررفت. در این شبیه‌سازی از داده‌های سه‌ساعته ECMWF (ERA Interim) برای واداشت‌های جوّی استفاده شده است. با توجه به قرار گرفتن دو رودخانه مهم کورا و سپیدرود در منطقه مورد مطالعه، ورودی این دو رود به مدل اِعمال شده است. نتایج مدل با داده‌های مشاهداتی و مدل‌سازی قبلی در دریای خزر اعتبارسنجی شده‌اند. بررسی‌ها نشان داد این مدل با مشاهدات میدانی و مدل‌های عددی اجراشده درگذشته همخوانی خوبی دارد. نتایج نشان می‌دهد تغییرات فصلی دما نسبت به شوری در این حوزه چشمگیرتر است. متوسط دمایی که مدل برای این حوزه برآورد کرده است، حدود 16 تا 18 درجه سانتی‌گراد است و مقدار میانگین برای شوری حدود 5/13 واحد شوری است. در بیشتر فصول، الگوهای جریان در این حوزه به‌صورت پادساعت‌گرد هستند. این الگوها که ناشی از وجود بادهای غالبی هستند که به‌صورت شمالی- جنوبی به سمت سواحل ایران می‌وزند، به شکل سواحل خزر جنوبی نیز وابسته‌اند. این جریانات سطحی که به‌ دلیل باد شکل می‌گیرند، با توپوگرافی خزر جنوبی کنترل می‌شوند و در بیشتر فصول، پیچک‌هایی را تشکیل می‌دهند که برخی از آنها دوقطبی هستند. مهم‌ترین نتیجه این تحقیق می‌تواند نوسانات حدود 5 تا 10 سانتی‌متری تراز سطحی خزر به دلیل وجود این پیچک‌ها باشد که بسته به چرخندی و واچرخندی بودن، می‌توانند تراز آب را افزایش یا کاهش دهند. بر اساس نتایج، هنگامی که پیچک‌ها چرخندی هستند، مرکز آب سرد تشکیل می‌دهند. این توده آب حدود نیم تا یک درجه سردتر از آب اطراف خود است. در پیچک‌های واچرخندی که مرکز گرم دارند، تراز آب‌های سطحی بیشتر از آب‌های اطراف است؛ ازاین‌رو این پیچک‌ها دو اثر مهم بر جای می‌گذارند که شامل تغییرات توزیع دمای سطحی و نوسانات سطح خزر است. البته نقش این پیچک‌ها را در پخش آلودگی‌های نفتی نمی‌توان نادیده گرفت.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical modeling of physical properties, currents and eddies in the Southern Caspian Sea

نویسندگان [English]

  • Javad Babagoli 1
  • Behzad Layeghi 2
1 M.Sc. Gradute, Oceanic and Atmospheric Science Centre (OASC), Tehran, Iran
2 Ph.D. Gradute, Oceanic and Atmospheric Science Centre (OASC), Tehran, Ira
چکیده [English]

The Caspian Sea is the greatest lake in the world. This basin plays a significant role in the climate of the countries located in the vicinity of it. This water body is divided into three basins, including the northern, middle, and southern parts. The Iranian coasts are located in the southern part. This paper uses the ROMS model to investigate the seasonal changes in physical oceanography phenomena in the Southern Caspian Sea. To deal with this, the model was run for seven years. The GEBCO data are utilized to make the grid file with the resolution of 30 seconds. Three-hourly ECMWF (ERA Interim) data was applied to the model. Furthermore, the Kura and the Sepidrud rivers were considered for simulation. The climatology and initial conditions data were extracted from World Ocean Atlas 2013 and ICOADS, respectively. In this research, the horizontal resolution of 2.5 km and 16 layers in vertical grids were applied to the model. The model outputs are validated with observation data and other simulations in this basin. The results show that the ROMS can be an appropriate model for simulation in this region, particularly in the southern part, as the outputs are compatible with the observation data. Moreover, the results indicate that the seasonal changes of temperature are remarkable compared to salinity.
    While the model has recorded the mean value of 16°-18° C for temperature, this value for salinity is 13.5 PSU. The typical surface currents are counter-clockwise as the dominant winds are from the north to the south towards the Iranian coasts. The topography of the southern part controls these currents because most eddies are formed in the vicinity of the deep part of the south part. Some eddies are dipoles that can be observable in most seasons. The strongest eddies are formed in this basin in the fall, particularly in December. The most important finding of this research can be the fluctuation of the surface water, which varies from 5 to 10 cm, due to these cyclonic and anticyclonic eddies. When eddies are cyclonic, they form the center of cold water. This water mass can be 0.5°-1° C colder than the surrounded water. Herein, we conclude that these eddies can have two considerable effects on sea surface temperature distributions and sea surface height. Thus, this model shows the behaviors of eddies correctly. It should be noted that eddies can play a significant role in the propagation of oil spills in the southern parts, which is discussed in this paper.
 

کلیدواژه‌ها [English]

  • Southern Caspian Sea
  • numerical modeling
  • currents and eddies
  • warm and cold core
  • changes in sea surface height
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