گردش کلی جو در اطلس و آرام شمالی و ارتباط آن با توسعه و تقویت واچرخندهای جنب‌حاره آزورز و هاوایی

نوع مقاله : پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه جغرافیای طبیعی، دانشکده جغرافیا، دانشگاه تهران، تهران، ایران

2 استاد، گروه جغرافیای طبیعی، دانشکده جغرافیا، دانشگاه تهران، تهران، ایران

3 استادیار، گروه جغرافیای طبیعی، دانشکده جغرافیا، دانشگاه تهران، تهران، ایران

چکیده

در این پژوهش به‌منظور شناخت ارتباط گردش کلی جو با توسعه و تقویت واچرخند‌های جنب‌حاره آزورز وهاوایی، تحلیل همدیدی-دینامیکی از وضعیت اقلیم‌شناختی گردش هادلی و گردش مداری (واکر) در حوزه اطلس و آرام شمالی به‌عمل آمده است. از روش تابع جریان جرم برای کمی‌سازی گردش نصف‌النهاری و مداری بهره گرفته شده است. داده‌های موردنیاز، شامل میانگین ماهانه مؤلفه نصف‌النهاری باد، سرعت قائم در دستگاه فشاری (اُمگا) و واگرایی باد افقی از نسخه ERA5، داده‌های بازتحلیل مرکز پیش‌بینی میان‌مدت وضع هوا (ECMWF) دریافت شده‌اند. الگوی گردش نصف‌النهاری میانگین نشان داد که انتقال جرم در تابستان نیمکره شمالی به‌سمت نیمکره جنوبی صورت می‌گیرد و گردش هادلی نمی‌تواند بیشینه فعالیت واچرخند‌های جنب‌حاره را تفسیر و توجیه کند. در حالی‌که الگو‌ی گردش نصف‌النهاری در سطح مقطع‌های کوچک‌تری در شرق اقیانوس‌ها، نشان داد که گردش هادلی نقش مهمی در انتقال جرم به جنب‌حاره نیمکره شمالی بازی می‌کند. براساس نتایج تحقیق، گردش هادلی در شرق اقیانوس‌ها، گردش مداری (واکر) ناشی از گرمای نهان آزاد شده در غرب اقیانوس‌ها و گردش حاصل از گرمایش بر روی خشکی‌های شرق اقیانوس‌ها نقش مهمی در انتقال جرم به جناح شرقی واچرخندهای جنب‌حاره دارند. فرایندهای مذکور در شکل‌گیری بادهای شدید شمالی در شرق اقیانوس‌ها و بادهای بسامان در منطقه حاره و در نتیجه آن، توسعه و تقویت واچرخندهای جنب‌حاره مؤثر هستند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The general circulation of the atmosphere in the North Atlantic and Pacific and its relationship with development and strengthening the Azores and Hawaiian subtropical anticyclones

نویسندگان [English]

  • Ali Akbar Garmsiri Mahvar 1
  • Ghasem Azizi 2
  • Hosein Mohammadi 2
  • Mostafa Karimi Ahmadabad 3
1 Ph.D. Student, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran
2 Professor, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran
3 Assistant Professor, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran
چکیده [English]

Subtropical anticyclones are among the large-scale atmospheric centers of action in the northern hemisphere in the east of the oceans. Clockwise flow and high surface pressure are two prominent features of these systems. These systems have an annual trend and usually achieve maximum flow and surface pressure in the summer, especially in July. Understanding the factors influencing the development and intensification of these anticyclones has been the favorite of many researchers. One of these factors has been the general circulation of the atmosphere. In this study, a climatological study of the general atmospheric circulation, including the Hadley and Walker circulations, has been performed. Their role in the development and strengthening of subtropical anticyclones has been investigated. The research has been done in three parts; 1- Mean Meridian Circulation, 2- meridional circulation in the North Atlantic and Pacific, and 3- Walker circulation in the North Atlantic and Pacific. In this study, the meridional component of wind, vertical velocity (omega), and horizontal wind divergence have been used. Data at 27 pressure levels with a horizontal resolution of 0.25 × 0.25 ° were extracted from the European Center for Medium Weather Forecasting (ECMWF) and the ERA5 version. The monthly mean of the data used was conducted over 40 years, from 1979 to 2018. The Mass Stream Function (MSF) method has been used to quantify the meridional and walker circulation.
The Mean Meridian Circulation showed that the meridional circulation in the equinox months consists of a pair of Hadley cells in which air rises in the tropics and subsides in the subtropics. Also, a solstitial cell is found with the ascent in the outer tropics of the summer hemisphere and subsidence in the outer tropics of the winter hemisphere. Although the Mean Meridional Circulation showed that mass transfer takes place in the summer of the Northern Hemisphere to the Southern Hemisphere and the Hadley circulation could not explain and justify the maximum activity of the subtropical anticyclones, but the meridional circulation at smaller cross-sections in the East Atlantic and Pacific showed that the Hadley cells play a vital role in mass transfer to the subtropics and mid-latitudes. The mean walker circulation (20-40 ° N) showed that the source of this circulation is only the latent heat released over the waters and the lands of the western oceans that have no role in mass transfer to the east. Westerly and southwesterly winds also form mass transfer in the Walker circulation to the northeast of the oceans. Heating in northwestern Africa and North America is another phenomenon that plays a role in subsidence in the North Atlantic and Pacific. The subsidence induced from heating on African lands is much more severe than that in North America. This may depend on the climate and extent of these areas. Therefore, as a result of this research, it can be said that three processes: Hadley circulation, Walker circulation, and heating on the lands adjacent to the eastern oceans, are effective in mass transfer and subsidence in the east Atlantic and Pacific. These conditions form strong northerly winds in the eastern oceans and trade winds in the tropics and effectively develop and strengthen subtropical anticyclones.

کلیدواژه‌ها [English]

  • General Circulation
  • Hadley Cell
  • Mass Stream Function
  • Subtropical Anticyclone
  • Walker circulation
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