تحقیقات کاربردی علوم جغرافیایی

تحقیقات کاربردی علوم جغرافیایی

بازتحلیل همدیدی سامانه های فشاری تابستانه موثر بر جو ایران

نویسنده
مهدی خزایی
دکتری اقلیم شناسی، دانشکده جغرافیا، دانشگاه تهران
10.52547/jgs.21.63.153
چکیده
بررسی‌های مربوط به سامانه‌های فشاری تابستانه موثر بر جو ایران، از دیرباز دچار چالش‌ها و بعضا تناقضاتی نسبت به یکدیگر بوده است. هدف این پژوهش، شناسایی نوع و فراوانی این سامانه ها از فشار تراز دریا تا فشار تراز 500 هکتوپاسکال می‌باشد. بدین منظور در سه ماهه فصل گرم سال(ژوئن، ژوئیه و اوت) از داده‌های میانگین فشار تراز دریا و ارتفاع ژئوپتانسیل فشار تراز 850 هکتوپاسکال مرکز پیش‌بینی میان مدت جوی اروپاییECMWF)) در دوره آماری 38 ساله(2016 ـ 1979) و از داده‌های ساعتی ارتفاع ژئوپتانسیل فشار تراز 500 هکتوپاسکال در ساعت UTC 12 مرکز ملی پیش‌بینی محیطی و مرکز ملی پژوهش‌های جوی ایالات متحدهNCEP/NCAR)) در دوره آماری 38 ساله( 2012 ـ 1975) استفاده شده است. نتایج پژوهش حاضر نشان می‌دهد که در فشار تراز دریا و فشار تراز 850 هکتوپاسکال، دو سامانه اصلی واچرخند آزور و مرکز کم‌فشار جنوب و جنوب غرب آسیا در منطقه جنب‌حاره قابل مشاهده است. جو کشور ایران در فشار تراز دریا و 850 هکتوپاسکال، تحت تاثیر زبانه‌های غرب‌سوی سامانه کم‌فشار موسمی بوده و شرق دریای مدیترانه، محل جدایش زبانه‌های غرب سوی سامانه کم‌فشار موسمی و زبانه‌های شرق‌سوی واچرخند آزور می‌باشد. در فشار تراز 500 هکتوپاسکال، 3 الگوی واچرخندی مستقل به نام‌های واچرخند آزور، عربستان و شمال غرب آفریقا و 4 الگوی واچرخندی ترکیبی منتج از سه الگوی فوق الذکر قابل تشخیص است. از میان واچرخندهای مستقل، واچرخند عربستان بیشترین و واچرخند آزور، کم‌ترین فراوانی را در جو تراز 500 هکتوپاسکال ایران تجربه می‌کند. در مقابل از میان واچرخندهای ترکیبی، واچرخند آزورـ شمال غرب آفریقاـ عربستان، بیشترین و واچرخند آزورـ عربستان، کمترین اثر را بر جو فشار تراز 500 هکتوپاسکال ایران دارد.
کلیدواژه‌ها
واچرخندهای جنب حاره‌ای
کم فشار جنوب آسیا
الگوهای فشاری
فصل تابستان
ایران

عنوان مقاله English

Reanalysis of summer pressure systems affecting Iran's atmosphere

نویسنده English

mahdi khazaei
PhD in climatology, university of Tehran
چکیده English

This study investigates the subtropical anticyclones and summer monsoons of the north hemisphere in the 500 hPa level, effective on Iran in a 38-year period (1975-2012). For this purpose, the data of geopotential heights of 500 hPa at 12 UTC with a spatial resolution of 2 by 2 degrees of the (NCEP/NCAR) were used. Results show that three independent patterns (Azores anticyclone, Saudi anticyclone and North West Africa anticyclone) and four combinatory patterns derived from the independent patterns have controlled the atmosphere of 500 hPa level of Iran. In most cases, the maximum in geopotential heights in above-mentioned anticyclone centers reach to more than 5920 geopotential meters, but often the tongue of these anticyclones control the atmosphere of 500 hPa levels of Iran with the geopotential height of 5880 to 5900 meters. In contrast, at this pressure level, the large-scale monsoon system is very weak and the maximum geopotential height of this system is about 5840 meters. The extent and intensity of the monsoon system has been reduced so that its tongues do not affect the 500 hPa level of Iran at any time. Given that the main factor in the development of large-scale monsoon system is the surface heating (bottom-up formation) and the main factor in the development of subtropical anticyclone is descending of atmospheric dynamics, the main reason for the development of summertime subtropical dynamic anticyclone should be a very strong and unit agent, something other than the summer monsoons.

کلیدواژه‌ها English

subtropical anticyclones
South Asia Low pressure
Pressure patterns
summer season
Iran
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