الگوهای همدید تعیین کننده مسیر حرکت سامانه‌های بارشی با منشاء سودانی

سامانه سودانی مهمترین سامانه تامین کننده بارش مناطق جنوبی ایران است. این سامانه در شرایط همدیدی مختلف، از مبادی ورودی و مسیرهای متفاوتی از ایران عبور می کند. هدف اصلی این تحقیق شناسایی و معرفی الگوهای همدیدی و سامانه های اصلی تاثیرگذار در تعیین مسیر حرکت سامانه سودانی می باشد. برای دستیابی به این مهم نیمه جنوبی ایران به سه منطقه جنوب غرب، جنوب میانی و جنوب شرق تقسیم گردید. با اعمال معیارهای لازم 142سامانه بارشی شناسایی شد. پس از استخراج منشا آنها هسته مرکزی، پهنه اولین منحنی بسته و محور اصلی زبانه کم فشارسودانی به تفکیک هر گروه استخراج شد. نتایج نشان می دهد موقعیت استقرار هسته و الگوی گسترش اولین منحنی بسته کم فشار در ماه های مختلف بارشی و سامانه های مسیرهای سه گانه، از لحاظ موقعیت مکانی تفاوت چندانی ندارد. بلکه مهمترین سامانه موثر در تعیین مسیر حرکت سامانه های سودانی واچرخندعربستان و الگوی گسترش ناوه شرق مدیترانه می باشد. در الگوی همدیدی سامانه های جنوب غرب، واچرخندعربستان در نیمه شرقی عربستان استقرار می یابد. محور ناوه ها دراین حالت عموما گسترش شمالیجنوبی دارند. درنتیجه پهنه و شدت بارش سامانه هایی که از جنوب غرب وارد ایران می شوند بیشتر از دو مسیر دیگر است. تمرکز محور ناوه های این مسیر بین طول های 30 تا 40 درجه شرقی (مدیترانه شرقی) می باشد. در سامانه های جنوب میانی واچرخندعربستان قدری جنوب سو شده و محوری شمال شرقیجنوب غربی پیداکرده است. در این الگو ناوه های مدیترانه ای عموما محوری شمال شرقیجنوب غربی دارند. در سامانه های جنوب شرق واچرخندعربستان با جابجایی شرق سوی نامتعارف برروی هند مستقر می شود. گسترش و امتداد محور ناوه ها و زبانه کم فشارسودانی مسیر جنوب شرق، دارای انضباط و هماهنگی ساختاری نمی باشد. این عدم تقارن را باید در توپوگرافی عمومی فلات تبت و الگوی گردشی مترتب در اثر حضور واچرخندتبت برآن جستجو کرد.

Synoptic Patterns that Determine the Trajectory of Precipitation Systems of Sudanese Origin

Synoptic Patterns that Determine the Trajectory of Precipitation Systems of Sudanese Originntroduction IntroductionPrecipitation as an important climatic element has many irregularities and fluctuations. Iran, especially its southern half, has significant precipitation fluctuations. Several atmospheric systems are involved in the formation of precipitation in this region from of Iran. Sudanese system is one of the most important precipitation systems in Iran. This system, in different synoptic conditions, enters Iran from different input sources and passes through Iran in different ways.The important and influential role of Sudanchr('39')s low pressure on precipitation in Iran, especially in the southern part of the country, has been repeatedly demonstrated in numerous studies. But the formation and its expansion have received little attention. These reasons have led to the consideration of the position of Sudanchr('39')s lowpressure synoptic expansion as an influential factor in the southern half of Iran precipitation. Therefore, the position of the expansion of this important climatic system has been investigated separately in the precipitation of the three regions south west, south middle and south east. Materials and MethodsTwo categories of data were used for this study. These data include daily precipitation data from the Iranian Meteorological Organization and the ERA interim gridded data include Sea Level Pressure (SLP) and the Geopotential Height of the 700 HP atmospheric level of the ECMWF. Second category data with horizontal resolution of 0.5 × 0.5 ° degrees during 19972017 statistical period were prepared.To achieve the purpose of the study, the southern half of Iran was first divided into three regions: SouthWest, SouthMid and SouthEast. After extracting daily precipitation of the selected stations in all three geographic regions, a total of 142 precipitation systems was identified by applying the required criteria. From this number of precipitation systems, respectively, were obtained in the south west 107, south middle 19 and southeast 16, respectively. Then, the source of precipitation systems was extracted using the atmospheric lower level maps. Subsequently, the central core and zone of the first closed curve around the Sudanese low pressure were extracted separately for each group. The main axis of the Sudanese lowpressure trough are also drawn on all rainy day. Finally, the model or pattern of atmospheric circulation in the precipitation systems of the regions is presented separately. Results and DiscussionThe purpose of this study was to determine the position of the central core and the pattern of expansion of the first closed curve around the Sudanese system and the Sudanese system trough in precipitation in each of the three regions of the southern half of Iran. Since the arrangement of precipitation systems may vary in different months of the year, depending on the general atmosphere of the atmosphere, the position of the core, the pattern of expansion of the lowpressure trough and the trough of 700hPa atmospheric level is analyzed separately each month.In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwestnortheast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally northsouth. As a result, the rainfall intensity and intensity of precipitation systems, entering the south west of Iran are higher than the other two routes. The focal point of troughs this route is between 30 to 40 ° east (Eastern Mediterranean). In systems with SouthMid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeastsouthwest axis. In this pattern, the Mediterranean troughs are generally northeastsouthwest. This pattern causes precipitation in the eastern half of the Iran. Or at least no precipitation in the northwest and west of the Iran.The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The troughs of this path showed two completely opposite patterns. In some systems, the troughs in the southwestnortheast direction with the orbital inclination, covers the whole of Saudi Arabia and southern Iran. On the contrary, in some systems the troughs stretch quite opposite to the first group, the northwestsoutheast direction.This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone. Basically Mediterranean troughs are disrupted in their usual eastward displacement after a longitude of 60 degrees. As you can see, the Sudanese lowpressure troughs for the SouthEast Route lack structural discipline and coordination. ConclusionThe results of this study show that the location and pattern of expansion of the first closed curve around low pressure in different precipitation months and systems of the three zones do not differ significantly in location. Rather, it is the most important system in determining the direction of Sudanese systems, the Arabian Subtropical High Pressure and the pattern of expansion of the eastern Mediterranean trough. In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwestnortheast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally northsouth. In systems with SouthMid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeastsouthwest axis. In this pattern, the Mediterranean troughs are generally northeastsouthwest. The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The Sudanese lowpressure troughs for the SouthEast Route lack structural discipline and coordination. This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone. Keywords: Synoptic Patterns, Sudanese Low Pressure system, Eastern Mediterranean Trough, Southern Half of Iran, Arabian Subtropical High Pressure.