Climatology of Jet Streams in the Middle East

Document Type : Full length article


1 Assistant Professor of Climatology, Faculty of Natural Resources, University of Kurdistan, Sanandaj, Iran

2 Professor of Climatology and Director of Center of Excellence for Spatial Analysis of Environmental Hazard, Kharazmi University, Tehran, Iran

3 MA in Climatology, University of Kurdistan, Sanandaj, Iran


One of the main elements of the general circulation in mid latitudes are the fast and narrow flow maxmia called jet streams whose speed is usually more than 30 meters per second. They are one of the dominant features of upper level weather maps but changing through time, space and layers of atmosphere. The jetstreams cause vertical motion underneath through which produce stability and instability over the earth surface. It should be mentioned that they are much known for their instability production. Jet cores are one of the main components of the general circulation and their location and displacement are controlled by the elements of the circulation such as the Arctic Oscillation. According to the researches, the location of the jet streams is very important in climate events. Therefore, this research tried to identify and present the location and speed of jet streams in Middle East. There was no comprehensive study in this scale so far.
Materials and methods
In order to study the jet streams, the six hourly (00, 06, 12 and 18 GMT) speed of U and V components of the winds at the 700, 600, 500, 400, and 300 hPa levels were obtained for the window of 0 to 120 E and 0 to 80 N during 1965-2014 period. In total, 20 time series were produced from the combination of these hour and level scales for each pixel with the size of 2.5 by 2.5 degrees. In each time series the wind maxima of 30 m/s and higher were extracted. At the final stage, the mean monthly speed and monthly frequency of jet streams of all pixels were mapped for the study area.
Results and discussion
The frequency and speed of jet cores were mapped and are described here in monthly, seasonal and annual scales. According to annual frequency of jet core locations, the highest speed maxima in 300 hPa level are located over the North Africa in 40 percent of times, depicting the main track of the jet cores. Given the fact that jet cores enter the study region only in the cold period of year, this temporal frequency of 40 percent is not a low value. The location of speed maxima is the same in 500 hPa level but in about 20 percent of the time. This low value is reasonable for this level. As we know, the synoptic systems of this level control most of the time the weather and climate of the surface and these surface systems are not very frequent during a normal year. In this level, the bifurcation of westerlies is obvious. The southern branch is very influential in the Middle East. This bifurcation indicates the presence of a blocking high in the region, which most of the times prevent the entering of jet cores and hence an unstable conditions over the region. There are no speed maxima in the region in 700 hpa level. Since in the annual scale only in the 500 and 300 hPa levels showed the jet cores, in the seasonal scale we look only for these levels. The frequency of jet cores in winter is more than the other seasons and show two separate belts. The jet core affecting the climate of Iran is passing over the Persian Gulf which extends from North Africa towards China. Jet cores pass through this belt all of the winter season. However, their frequency decreases toward the north over Iran and from there extends toward the other maxima over the latitude 50 N to 60 N. The jet frequencies have decreased in spring reaching to about 52 percent over the area (Figure 3B). This rate of decrease indicates the sudden and rapid change from winter to the spring conditions over Iran. Its northward shift is also obvious over Iran. In this season, the jet maxima travel in a ridge like track over Iran. It indicates an unstable weather over the west part of Iran while dominating the stable conditions over the east part of the country.
Jet streams are very important instability factors in the atmosphere. Their spatial location and speeds control the tracks of pressure systems and surface climate. For this reason, this study tried to understand their speed and spatial variations in the Middle East. Their speed and frequencies were studied at the pressure levels from 700 hPa to 300 hPa in the monthly, seasonal and annual scales. The result showed that in all levels and scales, two speed maxima tracks were established over the latitude belts of 20N – 30N and 50N – 60N which is confirmed by findings of Li et al (2004); Zhang et al ( 2006); Li and Wettstein( 2012) and Pena-Ortiz et al (2013). The most important findings of the research is the coincidence of speed maxima with frequency maxima of jet cores in these latitude belts. During the warm period, both the frequency and speed of the jet cores decreased over the Middle East. The jet cores were absent at the levels lower than 500 hPa, and in 300 hPa all winds experienced speeds higher than jet threshold which is in accordance with Geer et al (1996). In brief, we can conclude that through the fall season the jet cores move southward to dominate over the Middle East and Iran during winter. Through the spring season, they began backward movement to the northern latitudes so that in May no jet core could be found in the area. This research demonstrated the importance of the wind patterns of 500 hPa on the climate and weather conditions of the Middle East as well as Iran.


Main Subjects

حلبیان، ا.‌ح. و حسینعلی پورجزی، ف. (1393). تحلیل فراوانی رودبادهای مرتبط با بارش‏های حدی و فراگیر در کرانه‏های غربی خزر، فصل‌نامة تحقیقات جغرافیایی، 29(۱): شمارة پیاپی، 112: ۲۰۵-220.
عزیزی، ق. و سفرراد، ط. (1391). تحلیل ویژگی‏های رودباد طی فازهای ENSO مطالعة موردی؛ سال‏های 1997، 2008، و 2010، نشریة پژوهش‏های اقلیم‌شناسی، ۳(9): ۶۹-82.
علیجانی، ب. (1381). اقلیم‏شناسی سینوپتیک، تهران: انتشارات سمت.
فرج‌زاده، م.؛ لشکری، ح. و خورانی، ا. (1386). تحلیل موقعیت رودباد در رابطه با سامانه‏های بارشی غرب کشور (استان‌های ایلام و کرمانشاه)، مدرس علوم انسانی، 11(۵۳): ۲۳۹-256.
قائمی، ه.؛ عساکره، ح. و بیرانوند، آ. (1391). تحلیل احتمالاتی رخداد روزانة رودباد جنب حاره بر روی منطقة اقلیمی ایران، اندیشة جغرافیایی،  ۶(۱۲): ۶۹-86.
کاویانی، م.‌ر. و علیجانی، ب. (1379). مبانی آب و هواشناسی، تهران: انتشارات سمت.
محمدی، ب. و مسعودیان، ا. (1389). تحلیل همدید بارش‏های سنگین ایران، مطالعة موردی: آبان‌ماه 1373، جغرافیا و توسعه، 19: ۴۷-70.
مظفری، غ. و شفیعی، ش. (1396). تحلیل فضایی فراوانی رودبادهای مؤثر در بارش‏های فرین غرب ایران، پژوهش‏های جغرافیای طبیعی، 49(۱): ۸۵-100.
Azizi, Gh. and Safarrad, T. (2013). Analysis of Jet streams Characteristics during the ENSO Phases of Case Study; 1997, 2008, and 2010, Journal of Climatological Research, 3 (9): 69-82.
Alijani, B. (2002). Synoptic climatology, SAMT Publications, Tehran, Iran. 112-114.
Cook, K.H. (1999). Generation of the African Easterly Jet and Its Role in Determining West African Precipitation, Journalof Climate, 12: 1165-1184.
Crossley, A. and Parkinson, I. (1967). Distribution of Jet Streams at 200 mb. In the Middle East, Journal of Navigation, 20(4): 397-404.
Degirmendžić, J. and Wibig, J. (2007). Jet stream patterns over Europe in the period 1950–2001 – classification and basic statistical properties, Theoretical and Applied Climatology, 88(3-4): 149-167.
Du, Y.; Zhang, Y. and Xie, Z. (2009). Impacts of the zonal position of the East Asian westerly jet core on precipitation distribution during Meiyuof China, Acta Meteorol. Sin., 23: 506-516.
Farajzadeh, M.; Khorany, A. and Lashkary, H. (2008). The Relation between jet stream location and cyclones over the western Iran, American Journal of Applied Sciences, 5(10): 1308-1312.
Farajzadeh, M.; Lashkary, H. and Khorany, A. (2007). Analysis of jet stream position in relation to precipitation systems in the west of Iran (Ilam and Kermanshah Provinces), Modarres Human Science, 53: 239-256.
Geer, I.W.; Ginger, K.M.; Moran, J.M.; Hopkins, E.J.; Weinbeck, R.S. and Smith, D.R. (eds.) (1996). Glossary of weather and climate.American Meteorological Society, Boston, 272 pp.
Ghaemi, H.; Asakareh, H. and Bayranvand, A. (2012). Analysis of Probability Daily Occurrence Subtropical Jet Stream in Climate Region of Iran, Journal of Geographical Notion, 6(12): 1-44.
Halabian, A. and Hossainali Purjezi, F. (2014). The Frequency of Heavy Precipitation and comprehensive analysis of jet streams in the West Bank Caspian, Geographic Research, 112: 205-220.
Higgins, R.W.; Yao, Y.; Yarosh, E.S.; Janowiak, J.E. and Mo, K.C. (1997). Influence of the Great Plains low-level jet on summertime precipitation and moisture transport over the central United States, J. Climate, 10: 481-507.
Kaviani, M.R. and Alijani, B. (2002). Principles of Climatology, SAMT Press, 582 pp. (In Persian)
Kaviani, M.R. and Alijani, B. (2005). Foundations of climatology, SAMT Publications, Tehran, Iran.
Kumjian, M.; Evans, J.S. and Guyer, J. (2006). The relationship of the Great Plains low level jet to nocturnal MCS development , The 23rd Conference on Severe Local Storms (St. Louis, MO), Monday, 6 November 2006.
Kwon, M.; Jhun, J.-G. and Ha, K.-J. (2007). Decadal change in East Asian summer monsoon circulation in the mid-1990s, Geophys. Res. Lett., 34, L21706, doi: 10.1029/2007GL031977.
Landsberg, H.E. and Ratner, B. (1959). Note on frequency of high winds over the United States, Monthly Weather Review, May 1959 . DOI:;2.
Lewis, J.M. (2003). Ooishi's observation: viewed in the context of jet stream discovery, DOI:
Li, C. and Wettstein, J.J. (2012). Thermally driven and eddy-driven jet variability in reanalysis, J. Clim., 25: 1587-1596.
Li, C.; Wang, J.-T.; Lin, S.-Z. and Cho, H.–R. (2004). The relationship between East Asian summer monsoon activity and northward jump of theupper westerly jet location, Chin. J. Atmos. Sci., 28: 641-658.
Magata, M. (1950). On the Structure of the Jet Stream, Papers in Meteorology and Geophysics, 1(2-4): 175-187. DOI: 10.2467/mripapers1950.1.2-4_175.
Mohammadi, B. and Massoudian, A. (2010). Synoptic analysis of heavy rainfall events in Iran. Cause study November 1994, Geography and Development, 19: 70-47.
Mozafari, G. and Shafiee, S. (2017). Spatial Analysis of the Frequency of Jet Streams Influencing the Extreme Precipitation in Western Iran, Physical Geography Research Quarterly, 49(1): 85-100.
Pena-Ortiz, C.; Gallego, D.; Ribera, P.; Ordonez, P. and Alvarez-Castro, M.D.C. (2013). Observed trends in the global jet stream characteristicsduring the second half of the 20th century, J. Geophys. Res. Atmos., 118: 2702-2713, doi:10.1002/jgrd.50305.
Ren, X.; Yang, X.; Zhou, T. and Fang, J. (2011). Diagnostic comparison of winter time East Asian subtropical jet and polar-front jet: Large-scalecharacteristics and transient eddy activities, Acta Meteorol. Sin, 25: 21-33.
Riehl, H. (1948). Jet stream in upper troposphere and cyclone formation, Trans. Amer. Geophys.,Union, 29: 175-186.
Riehl, H.; Alaka, M.A.; Jordan, C.L. and Renard, R.J. (1954). The Jet Stream, Meteorological Monographs, Vol. 2, No. 7, American Meteorological Society, Boston, 1954, 100 pp.
Rossby, C.G. (1947). On the distribution of angular velocityin gaseous envelopes under the influence oflarge-scale horizontal mixing processes, Bull. Amer.Meteor. Soc., 28: 53-68.
Seilkopf, H. (1939). Maritime Meteorologie, Vol. 2, Handbuch der Fliegerwetterkunde, R. Habermehl, Ed., Radetzke, 150 pp.
Staff Members (1947). On the circulation of the atmosphere in middle latitudes, Bull. Amer. Meteor. Soc., 28: 255-280.
Strong, C. and Davis, R.E. (2008). Variability in the Position and Strength of Winter Jet Stream Cores Related to Northern Hemisphere Teleconnections, Journalof Climate, 21: 584-592.
Takahashi, K.; Uchida, E. and Nitta, T. (1987). A hundred years of meteorology (in Japanese), Shuppan News, 230 pp.
Tenenbaum, T. (1996). Jet Stream Winds: Comparisons of Aircraft Observations with Analyses, Weather and Forecasting, 11: 188-197.
Uccellini, L.W. and Johnson, D.R. (1979). The coupling of upper and lower tropospheric jet streaks and implications for the development of severe convective storms, Mon. Wea. Rev., 107: 682-703.
Walters, C.K. and Winkler, J.A. (2001b). Airflow configurations of warm season southerly low-level wind maxima in the Great Plains. Part II: The synoptic and subsynoptic-scale environment, Wea. Forecasting, 16: 531-551.
Walters, C.K. and Winkler, J.A. (2001a). Airflow configurations of warm season southerly low-level wind maxima in the Great Plains. Part I: Spatial and temporal characteristics and relationship to convection, Wea. Forecasting, 16: 513-530.
Xiao, C.; Zhang, Y.; Lofgren, B.M. and Nie, Yu. (2016). The concurrent variability of East Asian subtropical and polarfront jets and its implication for the winter climate anomaly in China, Journal of Geophysical Research: Atmospheres, doi/10.1002/2016JD025038.
Zhang, Y.; Kuang; X.; Guo, W. and Zhou, T. (2006). Seasonal evolution of the upper-tropospheric westerly jet core over East Asia, Geophys. Res.Lett., 33, L11708, doi: 10.1029/2006GL026377.
Hoflich, 0. (1961). Convection fronts and development of pressure pattern in the jet stream. Hamburger Geophysik. Einzelschr., 4: 91-186.
Scherhag, R. (1948). Neue Methoden der Wetteranalyse und Wetterprognose. Springer, Berlin·-Gottingen-Heidelberg, 424 S.
Plumley, W., 1994: Winds over Japan. Bull. Amer. Meteor. Soc., 75, 63–68.