تحليل روند جابجايي رودباد و پرفشار جنب حاره برفراز خاورميانه و رابطه آن با اقليم ايران

The Analysis of Transport Trend of Subtropical Jet Stream and High Pressure on Middle East and its Relationship with Iran Climate

در پژوهش حاضر از داده هاي مربوط به ارتفاع ژئوپتانسيل، مؤلفه مداري و نصف النهاري باد در ترازهاي 200تا700 هكتوپاسكال، در محدوده عرض جغرافيايي °0 تا ° 80 شمالي و طول جغرافيايي °10 درجه غربي تا ° 120 درجه شرقي بهره گرفته شده است. بازه زماني مورد استفاده شامل فروردين 1330 تا اسفند 1389 بوده است. داده هاي مورد استفاده از مركز ملي پيش بيني محيطي و مركز ملي پژوهش هاي جوي ايالات متحده آمريكا اخذ گرديده است. نتايج حاصل از بررسي روند فراواني سالانه رودباد بيانگر افزايش تداوم رودباد جنب حاره در مناطق جنوب پاكستان و شمال هند و كاهش تداوم آن در جنوب مديترانه مي باشد. در درياي سرخ، عربستان، خليج فارس، درياي عمان و كشورهاي عربي جنوب خليج فارس و همچنين ورودي چپ رودباد و درياي مديترانه تغييرات نصف النهاري در طي زمان، انحراف محور رودباد به شمال‌ را ممكن ساخته است. از طرفي بررسي روند پشته پرفشار جنب حاره نشان داد كه تداوم پشته مزبور بر روي منطقه از ابتداي دوره تا كنون روند افزايشي و معني دار داشته است. با در نظرگيري اينكه الگوهاي بزرگ مقياس جوي ارتباط تنگاتنگي با آب و هواي سطح زمين دارند، تغييرات زماني-مكاني آن ‌ها مي تواند سبب تغيير اقليم گردد.

Introduction In this study, temporal and spatial changes at subtropical jet stream and subtropical high pressure by climate change approach was considered. The position of northern edge of subtropical high pressure for a period of 52 years (1340 to 1391) were analyzed. Detection of northern edge of subtropical high pressure over Iran show that at the 400 hpa level and higher levels and at the 850 hpa level and upper levels cannot saw it. On this Based the three levels where the ridge was revealed and certain data were available, levels of 500, 600 and 700 hpa. Studies show that maximum speeds jet stream over Iran in winter and autumn, and a minimum of two months of July and August, respectively. Subtropical jet stream over Iran have caused maximum wind speed in the cold months. Impact of the jet stream northward motion in warm months (with the weakening of the polar vortex) have provided reduction of speed due to lack of thermal gradient in northern hemisphere. The results of the annual frequency jet stream indicate a continuing increase subtropical jet stream in southern Pakistan and northern India and reduce its continuation in the south of the Mediterranean. Also check the subtropical high pressure ridge height showed a continuation of mentioned ridge on Iran since the beginning of study time has had a significant and increasing. In view of the large-scale atmospheric patterns associated with climate of the Earth's surface, temporal and spatial changes can cause the climate changes. Materials and Methods In this present research, the related data to the geopotential height, zonal (U) and meridional (V) wind components of subtropical high presser ridge and wind for 42 (1340-1391) and 60 (1330-1389) years on confine of 20-80 north degree and (-10)- 120 east degree and in different levels has been taken from National Center for Eiwironmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) in order to investigate the position of subtropical high presser ridge and subtropical jet stream's seasonal trend. Then for investigation temporal spatial manners of subtropical high presser ridge and assessment its trend, the mean of north edge of geopotential height as an indicator of subtropical high presser ridge over Iran by used of four proviso computed. As well as to investigate the pattern of subtropical high pressure changes on Iran at three levels studied (700, 600 and 500 hp}, annual trend for data geopotential height (hgt) by use programming features the pre-application environment Grads was extracted was calculated. To calculate the linear regression was used. As well as to investigate the pattern of subtropical high pressure changes on Iran at three levels studied {700, 600 and 500 hp), annual trend for data geopotential height (hgt) calculated. To calculate the linear regression was used. In order to create changes pattern in annual time series, analysis of trend of jet stream has been paid. In line with investigation of trend in the jet stream passed two processes; after calculating the trend of speed in a separate process with the aim of achieving the trend of axis at jet stream, zonal and meridional components of the jet stream were examined. Discussion and Conclusion The occurrence of subtropical jet stream and its result the subtropical high pressure ridge, in particular latitude like border that represent two types of air water is in the north and south. The results of investigation of subtropical high presser ridge in this ' study show that ridge intensity and activity on Iran, particularly in the West and North-west is increased. Changes in the speed and axis of subtropical jet stream indicates climate change at the area in the near future. As well as Increase subtropical jet stream shifts to the north has been caused greater extent of IRAN· affected by this system. On the one hand occurrence of changes in the meridional jet stream and the subtropical high pressure in the spring can strengthen the important phenomena such as heavy precipitation and severe dust in parts of West and North West of the country. Moreover, the subtropical jet stream core route in a way that is able to transfer moisture (from the Mediterranean Sea and the Red Sea) and dust (dust sources in North Africa, Saudi Arabia and Iraq) respectively.