Trend Analysis of the Recent Seasonal Changes in Subtropical Jet Stream in Climateof Iran

Document Type : Full length article

Authors

1 Associate Professor of Climatology, Department of Geography, University of Zanjan, Zanjan, Iran

2 Professor Meteorology, Faculty of Climatology Research, Tehran, Iran

3 MA Student of Synoptic Climatology, University of Zanjan, Zanjan, Iran

Abstract

Introduction
According to the definition of World Meteorology Organization (WMO), as the speed of the air mass is more than 30 meters per second, the jetstream will arise. The core of the jetstream is with baroclinic atmosphere due to the large difference in temperature and wind speed. There are two west jetstreams in the northern hemisphere. The northern jet stream is called polar front jetstream and the southern is called subtropical jetstream. Polar Front Jet Stream produce intense temperature gradient by polar air mass and tropical Polar Front Jet Stream is produced by strong temperature gradient of polar and subtropical air. The subtropical jetstream is produced by temperature gradient in tropopause as limited to the upper troposphere. Subtropical jetstream situation is able to show a seasonal shift, this seasonal displacement of subtropical jet stream can cause the tropical and extra tropical alternative regimes on climate of Iran. The seasonal movement of extra tropical jetstream causes intermittent exposure regimes in tropical and extra tropical. When the jetstream is located over the south of Iran in the cold period of the year, extra tropical climatic factors enter into Iran such as westerliesand cyclones. While jet stream is in northern part of Iran in the warm period of the year, tropical climatic factors will enter Iran. Therefore, recognition of position of this phenomenon is necessary for detecting temporal changes of the other spatial atmospheric phenomena affecting the climate of Iran. On the other hand, possible behaviors in different situations can be recognized by accessing to the jet stream event.
Studies have indicated that the mean latitude of the sub-tropical jet stream in both hemispheres have shifted toward the poles over the last few decades; while, the little changes in the jet stream position has huge effects on the distribution of temperature, precipitation and weather patterns. Therefore, it seems necessary to analysize the climate phenomenon, more than ever.
 
Materials and Methods
In this present research, the related data to the zonal (U) and meridional (V) wind components of for a 60 years period (from 20-80 north degree and -10/-120 east degree and in 200 hap) has been derived from National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) in order to investigate the subtropical jet stream’s seasonal trends. To perform seasonal analysis, the data have been separated in seasonal scale by MATLAB. According to the placement of maximum speed in all of the seasons in 200 hap high level, the computation of related process is centralized on these high level data. The computation has been accomplished by liner regression and by the use of Least Square Error (LSE) method. Their result of spatial distribution has been drawn by SURFER software.
 
Results and Discussion
The results of descriptive analysis in this research show that the maximum speed has been occured in winter and the minimum speed in the summer. The altitudinal range of this phenomenon in the winter is more than the summer. The results of review processing in 4 seasons have been exposed in the study area and the significant trend is 10, 2.9, 11, and 10 % for spring, summer, fall and winter, respectively. The interesting point in this result represents the maximum occurrence of significant equinox seasons. However, the researches were mainly conducted on winter season and there isn’t any research about equinox seasons.
 
Conclusion
The results of this study have revealed that subtropical jet stream’s intensity is likely to be reduced in fall and spring in the future century. The results are in a confidence level of 95%. On the other hand, investigation about the zonal and meridional wind component trends of jet stream has displayed in the seasonal changes. The maximum percentage of Eastward changes has occurred in winter than any other season of the year. This has surrounded 7.4 percent of the area. These are occurred in conformity of the jet stream axis in east of Iran, Afghanistan, Pakistan, and India. Northward changes have represented the highest rate in the spring and fall with 10.6, 8.4 percents in the core of jet stream. In summer the trend is significant only in 2.5 percent of the study area. The major changes have occurred in the input and output of jet stream core, and eastward changes has occurred only in this season in winter, northward changes has occurred in 0.7 percent of the area and the eastward changes has occurred in 7.4 percent of the area.

Keywords


امیدوار، ک. (1389). آب‌و‌هواشناسی همدیدی، یزد: انتشارات دانشگاه یزد.
ترابی، ع.‌ا. (1355). جتاستریم روی ایران، پایان‌نامة کارشناسی ارشد هواشناسی، تهران: دانشگاه تهران.
خورانی، ا. (1384). تعیین موقعیت جت در رابطه با سامانههای بارشی غرب کشور در دورة زمانی 1999-1990، پایان‎نامة کارشناسی ارشد اقلیم‎شناسی و برنامه‎ریزی محیطی، به‌راهنمایی منوچهر فرج‌زاده‌اصل و حسن لشکری، تهران: دانشگاه تربیت مدرس، گروه جغرافیا.
زرین، آ. و مفیدی، ع. (1384). وردشپذیریفعالیتخورشیدیواثرآنبراقلیمزمین (مطالعةموردی:اقلیمخاورمیانهوایران)، فصل‎نامة جغرافیایی سرزمین، سال 2، شمارة 8 ،ص. 83-104.
عابدینی، ی.؛ ذوالفقاری نیک‌انجام، س. و بیرانوند، آذر. (1391). تحلیل آلودگی هوای شهر زنجان با استفاده از مدل‌های هواشناسی و رابطة آن با جت‌استریم جنب حاره(مطالعة موردی: طوفان گردوغبار 04/12/1388)، اولین همایش ملی حفاظت و برنامه‌ریزی محیط زیست، 13 اسفند 1391، همدان.
عزیزی، ق. و سفرراد، ط. (1391). تحلیل ویژگی‌های رودباد طی فازهای ENSO (مطالعة موردی: سال‌های 1997، 2008، 2010)، نشریة پژوهش‌های اقلیم‌شناسی، سال 3، شمارة 9،ص. 69-82.
عساکره، ح. (1390). مبانی اقلیم‌شناسی آماری، زنجان: انتشارات دانشگاه زنجان.
علیجانی، ب. و هوشیار، م. (1387). شناسایی الگوهای سینوپتیکی سرماهای شدید شمال غرب ایران، مجلة پژوهش‎های جغرافیای طبیعی، شمارة 65، ص. 1-16.
علیجانی، ب. (1374). آب‌و‌هوای ایران، تهران: انتشارات دانشگاه پیام‌نور.
فرج‌زاده‌اصل، م.؛ لشکری، ح. و خورانی، ا. (1386). تحلیل موقعیت رودباد در رابطه با سامانه‌های بارشی غرب کشور ( استان‌های ایلام و کرمانشاه)، مجلة مدرس، دورة 11،شمارة 53، ص. 239-256.
کاظم‎پور، ع.ر. (1357). بررسی حالات خاص رودبادها روی ایران، پایان‎نامة کارشناسی‎ ارشد هواشناسی، تهران: دانشگاه تهران.
کاویانی، م.ر. و علیجانی، ب. (1385). مبانی آب‌و‌هواشناسی، تهران: سازمان مطالعه و تدوین کتب علوم انسانی دانشگاه‎ها.
مرادی، م. (1390). مقدمه‌ای بر هواشناسی دینامیکی 1، انتشارات سید‌باقر حسینی.
مسعودیان، ا. (1390). آب و هوای ایران، انتشارات شریعه توس، اصفهان، 1390.
معصومی، ا. (1391). مطالعة پارامترهای فیزیکی هواویزهای جو زنجان با استفاده از اندازه‌گیری‌های شیدسنج خورشیدی، داده‌های ماهواره‌ای و مدل‌های هواشناسی HYSPLIT و NCAP/NCAR، پایان‌نامة دکتری فیزیک، به‌راهنمایی محمدرضا خالصی فرد، زنجان: دانشگاه تحصیلات تکمیلی علوم پایه (گاوازنگ-زنجان).
مفیدی، ع. و زرین، آ. (1384). بررسیسینوپتیکیتأثیرسامانه‌هایکم‌فشارسودانی دروقوعبارشهایسیل‌زادرایران، مجلة تحقیقات جغرافیایی، شمارة 88، ص. 113-139.
Abedini Y.A., Zolfaghari S. and Beyranvand A., 2013, The Analysis of Air Pollution at Zanjan City With Use from Meteorology Models and Relationship with Subtropical Jetstream, The 1rd National Symposium Environmental Planning, Hamedan.  
Alijani B., 1995, Climate of Iran, Tehran: Piam Nour University.
Alijani B., Houshyar M., 2008, Identify Synoptic Patterns of Drastic Colds in North-Weast of Iran, Journal of Research of Natural Geography, No. 65, pp. 1-16.
Archer, C.L. and Caldeira, K., 2008, Historical trends in the jet Streams, Geophys. Res. Lett., 35, L08803.
Asakereh. H, 2011, Fundamentals of Statistical Climatology, Zanjan: Zanjan University [In Persian].
Azizi GH. and Safarrad T., 2013, Analysis of Jet Stream’s  traits in phases of ENSO, Research of Climatology, No 9, pp. 69-82. 
Baldi, M., Dalu, G., Maracchi, G., Pasqui, M. and Cesarone, F., 2006, Heat Waves in the Mediterranean: A Local Feature or a Larger-Scale Effect? , International Journal of Climatology, Int.J.Climatol.26, 1477-1487.
Eicher, T. and Higgins, W., 2005, Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity. Journal of Climate, No. 19, pp. 2076-2093.
Farajzadehasl M., Lashkari H. and Khorani, A., 2005, Analysis of Jet Stream Position in Relation to rainfall Systems in West Iran (provinces of Ilam and Kermanshah Stations), Journal of Modares,No. 53, pp. 239-256.
Hudson, R.D., 2012, Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010, Atmos. Chem. Phys, No. 12, pp. 7797–7808.
Johnson, D.H. and Daniels, S. M., 1954, Rainfall in relation to the jet stream, Quartery Journal of The Royal Meteorological Society, No. 80, pp. 212-217.
Kavyani M. and Alijani B., 2006, The Foundations of Climatology, 12st edition Tehran: SAMT. Organization, [In Persian]. 
Kazempour A., 1979, Jet Stream Over Iran, Thesis Submitted For The Award of M. S Degree In Meteorology, Supervisors: Prof. P. Koteswaram, Ph. D Khirandish, Ph. D. A. Zand. Tehran: University Geophysics College.
Khorani, A., 2005, Jet Stream Positioning associated with the rainfall Systems West of Country in the period 1990-1999, Thesis Submitted For the Degree of M. S Degree in Climatology, Supervisors: Ph. D M. Farajzadehasl, Ph. D. H. Lashkari, Tehran: Tarbeyat Modares University. 
Lewis, J. M., 2003, Ooishi's Observation: Viewed in the Context of Jet Stream Discovery. Bull.American Meteorological Society, No. 84, pp. 357–369.
 Masoodian A., 2008, Identification of synoptic conditions associated with rainfall Extreme in Iran, 3rd Conference Management Water Sores Iran, 23 till 25 October 2008, Tabriz: University of Tabriz.  
Masoumi A., 2012, Investigation of Physical Parameters of Aerosols in Atmosphere Measurements, Satellite Data, HYSPLIT and NCEP/NCAR Models, Ph.D Thesis, Supervisor: Dr. Hamid Reza Khalesifard.
Mofidi A., Zarin A., 2005, Review Synoptic Effect SUDAN’S Low Presser Systems at Occurrence Rainfall in Iran, Journal of Geography Research’s, No. 88. pp. 113-139.
Mohler, S.R., Bobby, H.J and Post, W., 1971, His Winnie Mae, and the World's First Pressure Suit, Smithsonian Institution Press, City of Washington.
Moradi M., 2011, An Introduction to Dynamic Meteorology 1, Educational Center of Applied Science and Technology For Meteorological and Atmospheric Science of Tehran, Sayed Bagher Hossain.
Omidvar, K., 2010, Synoptic Climatology, Yazd: University of Yazd.
Prezerakos, N.G., Flocas, H.A. and Brikas, D., 2006, the role of the subtropical jet in a case of depression rejuvenation over the Eastern Mediterranean interaction between polar; Meteorology Atmospheric Physics 92, pp. 139–151.
Rodionov. Sergei and Assel, R., 2001, A New Look at the Pacific/North American Index, Geophysical Reserch Letters; No. 28, pp. 1519-1522.
Seager, R., Harnik, N., Robinson, W.A., Kushnir, Y., Ting, M., Huang, H.P. and Velez, J., 2005, Mechanisms of ENSO-forcing of Hemispherically Symmetric Precipitation Variability, Q. J. R. Meteorol. Soc. No.131, pp.1501–1527.
Strong, C. and Davis, R. E., 2007, Variability in the Position and Strength of Winter Jet Stream Cores Related to Northern Hemisphere Teleconnections, Journal Of Climate, No. 21.
Torabi. A. L., 1976, Jet Stream over Iran, Thesis Submitted For the Degree of M. S Degree in Meteorology, Tehran: Tehran University Geophysics College.
Woollngs, T. and Blackburn; M., 2012, the North Atlantic Jet Stream under Climate Change and Its Relation to the NAO and EA Patterns; Journal of Climate, No. 25, pp. 886-902.
Xuejuan, R., Xiuqun, Y., Tianjun, Z. and Jiabei, F., 2010, Diagnostic Comparison of Wintertime East Asian Subtropical Jet and Polar-Front Jet: Large-Scale Characteristics and Transient Eddy Activities.
Zarin A., Mofidi A., 2005, Variation of solar activity and its effects on Earth's climate (Case Study: Climate in the Middle East and Iran), Geography of Land, No. 8, pp. 83-104.
http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanaly.