تحلیل سینوپتیکی بارش¬های حوضه¬های اترک وگرگان¬رود (39 بارش فراگیر) دکتر محمد باعقیده ، دکتر علیرضا انتظاری ، فاطمه علیمردانی

نوع مقاله: مقاله پژوهشی

10.22111/gdij.2012.433

چکیده

به منظور تحلیل سینوپتیکی بارش­های حوضه­های اترک و گرگانرود در شمال شرق ایران، 39روز با بارش فراگیر بیش از 7 میلیمتر طیّ دوره­ی آماری 6 ساله (2002-1997) انتخاب شد. سپس داده­های شبکه­بندی شده­ی فشارسطح دریا مربوط به  (65-10 عرض جغرافیایی و 80- 5 طول جغرافیایی) با تفکیک مکانی (2.5×2.5) درجه مربوط به روزهای منتخب بارشی از پایگاه داده (NCEP/NCAR) استخراج گردید.
بر روی این داده­ها تحلیل عاملی و سپس تحلیل خوشه­بندی سلسله مرتبی با روش ادغام ward انجام گرفت بر اساس این تحلیل 6 الگوی سینوپتیکی در سطح زمین تشخیص داده شد که بر این اساس الگوهای مربوط به سطح 500 نیز استخراج گردید. نتایج نشان می­دهد در الگوهای  سطح زمین تقابل یک مرکز پر­فشار نسبتاً قوی در سمت غرب یا شمال­غرب و مرکز کم­فشاری در مرزهای شرقی ایران کاملاً مشهود است. علاوه برآن الگوهای استخراج شده برای ارتفاع ژئوپتانسیل در سطح 500 نیز همواره حضور یک فرود را بر روی ایران نشان می­دهد.

کلیدواژه‌ها


عنوان مقاله [English]

Synoptic Analysis of Rainfall in Atrak and Gorganroud Basins (39 Pervasive Rainfall) Dr. Mohammad Baaghideh Assistant Professor of Natural Geography University of Tarbiat Moallem Sabzevar Dr.Alireza Entezari Assistant Professor of Natural Geography University of Tarbiat Moallem Sabzevar Fateme Alimardani M.S of Climatology University of Tarbiat Moallem Sabzevar

چکیده [English]

Introduction
Synoptic climatology term was used for the first time in U.S.A Air force at 1940s decade. Their goal of this field is  to  analyze  the  previous  frequencies  of  climatic  components  and forecast  the  atmospheric condition  based  on  the  computations. Synoptic climatology provides useful tools for the researchers in the fields of atmosphere, environment and geography sciences and at the present it is the most rapid way to recognize the relationship between environmental processes   and atmospheric cycles. today, the study of relevant different phenomenon of the climate including  draughts,  severe  rainfalls,  pollution  and  storms  and . . .by the use of synoptic methods  presents  a more  acceptable  results and  more  reliable predictions.  Aatrak and Gorganrood are the most important rivers in northeastern part of Iran and Caspian Sea catchment area. Wide farmlands and numerous cities and towns with considerable population and also different water structures including bridges and dams are located in this area and being affected by the discharge fluctuations.
Since  the  type  and  rate of  rainfalls  has  an  important and determinant role   on the  catchment area reactions  , knowing  the  dominant  Synoptic  patterns  may  be  efficient  to  forecast  pervasive  rainfalls  or heavy rain falls flood discharge  and can be considered and used in different economical  activities and planning  particularly agriculture, transportation , tourism and ...
 
Research Methodology
This research from objective view is of applied research and is of descriptive-analytical method. The main data were obtained from National Centre of Environmental predictions (NCEP/NCAR) data base.. In  this  research, Environment  to  Circulation  technique  is  used  as  the  initial  principle .It means that circulatory patterns shall provide the criteria which are determined based on the environmental variables. In  Synoptic  analyses, a  combination  of  qualitative  and  quantitative  methods  (using  maps  and  numerical  data together) have been used.





 
Synoptic Analysis of Rainfall in Atrak and Gorganroud Basins …
 
 
 
 





The  processes  of  classifying  and  arranging  data  are  performed  by  the  Excel  software and  also  the  data  analysis process  by the use of descriptive  and  inferential  statistic  methods, like  the  factor  analysis  and  clustering  have been performed  by SPSS  software.
 
Discussion and Results
In this research, environment to circulation synoptic method has been used in the main initial principle. Among  the  available  stations, Five  Synoptic  stations  were  selected  with  suitable  dispersion through  analyzing  the  rainfall  data,  39  days  with  more  than  7mm            of  rainfall which were common in  all the stations have been selected as pervasive rainy days . This research has been performed by using daily data of sea level pressure (SLP) which were obtained at the area of 12.5◦ up to 60◦ north latitude degree and 5◦ up to 80◦ of east longitude degree with spatial resolution of 2.5 arch degrees were obtained from National Centre of Environmental Predictions (NCEP/NCAR). For each day a 21* 30   matrix was formed and the data of  each  matrix  ( each day one matrix) is reformed  by  the  Excel  software  in to a  row, from  left  to  right  and  39  rows  together  formed  a  new  matrix  with dimension   630*  39.
The  pressure  data  for  the  rainy  days  was  summarized  by    factor  analysis  technique. After deriving the main factors, factor scores were used in clustering as the main data. The  clustering technique classifies all the observations based on their distance, so the similar observations are combined together and more similar observation   are combined in the next step. In this research, applied hierarchical cluster analysis by using Ward linkage method in SPSS soft ware was applied on factor scores. Finally the main groups have been formed regarding Environment to circulation curves and based on dendrograms curve of earth surface data, 6 synoptic patterns were derived.
 
Conclusion
The obtained results from analyzing the derived patterns related to earth surface and upper levels of atmosphere are summarized as follows:
Regarding to the derived patterns of sea level maps, the existence of a relatively high pressure center in  the west or northwest parts of Iran and a low pressure center was identified in east of Iran for the rainy days. The contact of the centers together (which are considered as the transitive systems based on the type) may be efficient to provide the area rainfall mechanisms beside to increase the pressure gradient.
The role of the Siberian high pressure decreasing the temperature and increasing the pressure gradient is absolutely obvious for two sea level patterns. Also the north eastern mountains of Iran were efficient to improve the high pressure locally on earth but generally the existence of a low pressure in eastern part  of Iran or being located between two low pressure and high pressure center as the under study area was the most  important earth surface pattern for rainfalls.
The under study  area was located in front  of or under a trough based on the derived patterns in 500hp level maps  in most rainy days  which it makes instable conditions and it also provides ascent factor. Furthermore, the existence of a trough on north of Iran was observed in 500 hp level patterns and the main differences are more correlated with the trough axis deviation and also related to its depth.
 
Keywords: Factor Analysis, Synoptic Patterns, Clustering, Atrak and Gorganroud Basins.     
 
 
 
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کلیدواژه‌ها [English]

  • Factor Analysis
  • Synoptic patterns
  • Clustering
  • Atrak and Gorganroud Basins