نقش باد و الگوهای جوی در مکان¬گزینی و جهت ریگزارهای دشت کویر

نوع مقاله: مقاله علمی پژوهشی

نویسندگان

1 دانشیار دانشکدۀ جغرافیا

2 استادیار دانشکدۀ جغرافیا

3 استادیار ژئومورفولوژی، دانشگاه یزد

چکیده

به‎دلیل شرایط اقلیمی خشک دشت کویر، پهنه­های ماسه­ای عمده­ای در قسمت­های مختلف آن پراکنده شده است. در مکان­گزینی و جهت­گیری این پهنه­های ماسه­ای، عوامل مختلفی نقش دارند که از مهم‎ترین آنها می­توان به توپوگرافی و جهت باد غالب اشاره کرد. از آنجا که باد یکی از عوامل مؤثر در تولید تپه­های ماسه­ای و استقرار آنها است، می­توان با استفاده از آمار باد ایستگاه­های هواشناسی و رسم گل­باد، جهت و سرعت باد را تعیین کرد. با توجه به اینکه در محدوده‎ی دشت کویر، به‎دلیل شرایط نامساعد طبیعی، ایستگاه­های هواشناسی محدود است، بنابراین از داده­های دینامیک جو برای مطالعه‎ی جهت باد در سطح دشت کویر و ریگزارهای مورد مطالعه استفاده شد. برای این امر با توجه به میانگین ارتفاع دشت کویر (درحدود 700 متر)، داده­های مربوط به سطح فشار 925 هکتوپاسکال، برای تعیین نوع وزش بادهای فصل تابستان، به‎منزلۀ دورۀ خشک دشت کویر مورد استفاده واقع شد. بادهای مداری غالب شرقی ـ غربی و بادهای نصف‎النهاری شمالی ـ جنوبی در سطح دشت کویر به‎همراه توپوگرافی قسمت‎های جنوبی و جنوب غربی، سبب تراکم بیشتر ریگزارها در این قسمت­های دشت کویر شده است. با استفاده از داده­های حاصل از بادهای مداری و نصف‎النهاری، جهت بادهای تابستانی در قسمت‏های مختلف دشت کویر مشخص شد که تا حدود زیادی با جهت گل‏بادهای ایستگاه‏های هواشناسی و نوع مورفولوژی عوارض ماسه­ای در تصاویر ماهواره‏ای منطبق است. مطالعۀ جهت بادهای تابستانی، نشان‎دهندۀ وجود دو سامانۀ فشار متفاوت مؤثر در جهت‌گیری ریگزارهای واقع در نیمۀ شرقی و غربی دشت کویر است.

کلیدواژه‌ها


عنوان مقاله [English]

Impact of Wind and Atmospheric Patterns in Location and Direction of Dasht-e Kavir Ergs

نویسندگان [English]

  • Mehran Maghsoudi 1
  • Mojtaba Yamani 1
  • Faramarz Khoshakhlagh 2
  • Ali Shahriar 3
1 Associate Prof., Faculty of Geography, University of Tehran
2 Assistant Prof., Faculty of Geography, University of Tehran
3 Assistant Prof. of Geomorphology, Yazd University
چکیده [English]

Introduction
In climate, Iran is a part of the Afro-Asian belt of deserts. This climate is almost rainless and has very arid climatic condition. The desert soils are mainly covered with sand and pebbles. These materials are largely carried by the wind. Dasht-e Kavir is a large desert lying in the middle of the Iranian plateau (at longitudes from 58 ̊ to 53 and Latitudes from 36 ̊ to 32́). As the desert is surrounded by Alborz and Zagros Mountains, the moisture cannot penetrate into the desert area. In summer, Establishment of the Azores high pressure account for the dry conditions in the Dasht-eKavir. These conditions reduce the total amount of rainfall and the lack of sufficient vegetation in the Desert. Therefore, Wind has a high potential for Erosion, Transport and accumulation of Sediment. As a result, the conditions for the formation of Ergs and Sand sheets are provided in the desert. Furthermore, Dasht-e Kavir was surrounded by various high lands so that they are the most effective factor in the deposition of sand and switching in location of Ergs. The temperature difference in Desert mountain ranges is always a generator for different daily local wind. The local winds can play important role in morphological changes of the Desert Surface.
Methodology
Formation of dune areas is determined by the production of sediment by a range of suitable particle sizes, the availability of the sediment for transport by wind, and the transport capacity of the wind. In this Study, satellite images were first obtained to reconnaissance the location of the study area. Thus, the location of highlands and the scattering of Khartouran, Chah Jam, Sargardan And Jen Ergs around the dasht-e Kavir was examined by observation DEM, ETM+ ,MSS and Google Earth Images through ArcGIS Software. By this, the role of highlands of the concentration and accumulation of Sand is observed.
Second, Ergs morphology is detected on the satellite images. Prevailing wind direction was determined based on Ergs Landforms. Prevailing winds around the desert, Wind Rose, was identified via Wind data from meteorological stations by WRPLOT Software. In addition, U-wind and V-wind in Dasht-e Kavir was examined by wind dynamics data from 925 HP leveland PANOPLY Software.
Third, the vorticity of summer in Dasht-e Kavir has been Examined in relationship to Ergs morphology by dynamics data 925 HP level via PANOPLY Software.
 
Results and Discussion
The results of morphological effects on satellite images and their relationship with local wind regime have illustrated that Wind regime in the Dasht-e Kavir was coincident with Ergs Morphology so that Wind direction and Ergs Morphological, follows from a process of convergence. Sand roses for summer around Dasht-e Kavir have been shown to be in east to west in the half Northing, while in the southern part of the Desert they have been west to eastern winds. Desert U- winds are more oriented to the East-west while the most of V- winds in the desert have a North - South.
Vorticity of the desert in summer also represents a trend in the direction of rotation. The Vorticity of the desert in summer also represents a trend in the direction of rotation in Anti- clockwise.
 
Conclusion
Ergs Morphology is corroborated in common systematic morphogenesis in the Dasht-e Kavir. This common Systematic morphogenesis around the desert represents a spatial route, Sothat the morphology of the north- east of Dasht-e Kavir, sand Khartouran, is North East - South West. This trend is changing with the movement to the west so that vary to North – South direction in Chah Jam Erg. These winds continue to Northern Rig-e Jen and in the southern parts of the Rig-e Jen divert towards North West- South East and West – East direction in Choupanan Town.
Concurrent review Vorticity and Erg morphology around the Dasht-e Kavir, represents the interaction between Ergs morphology and weather patterns so that Ergs Morphology and Patterns of weather have a convergent path. Thermal low pressure system is generated in Dasht-e Kavir in Summer so that direction of rotation in thermal low coincides with the Erg Morphology around Dasht-e Kavir. Therefore, the topography has influenced the situation of Ergs, Vorticity and Wind direction has been effective in Ergs morphology.

کلیدواژه‌ها [English]

  • Dasht-e Kavir
  • Erg
  • Weather Patterns
  • U-wind
  • V-Wind