نقش باد و الگوهاي جوي در مكان گزيني و جهت ريگزارهاي دشت كوير

به‎دليل شرايط اقليمي خشك دشت كوير، پهنه هاي ماسه اي عمده اي در قسمت هاي مختلف آن پراكنده شده است. در مكان گزيني و جهت گيري اين پهنه هاي ماسه اي، عوامل مختلفي نقش دارند كه از مهم‎ترين آنها مي توان به توپوگرافي و جهت باد غالب اشاره كرد. از آنجا كه باد يكي از عوامل موثر در توليد تپه هاي ماسه اي و استقرار آنها است، مي توان با استفاده از آمار باد ايستگاه هاي هواشناسي و رسم گل باد، جهت و سرعت باد را تعيين كرد. با توجه به اينكه در محدوده‎ي دشت كوير، به‎دليل شرايط نامساعد طبيعي، ايستگاه هاي هواشناسي محدود است، بنابراين از داده هاي ديناميك جو براي مطالعه‎ي جهت باد در سطح دشت كوير و ريگزارهاي مورد مطالعه استفاده شد. براي اين امر با توجه به ميانگين ارتفاع دشت كوير (درحدود 700 متر)، داده هاي مربوط به سطح فشار 925 هكتوپاسكال، براي تعيين نوع وزش بادهاي فصل تابستان، به‎منزله دوره خشك دشت كوير مورد استفاده واقع شد. بادهاي مداري غالب شرقي ـ غربي و بادهاي نصف‎النهاري شمالي ـ جنوبي در سطح دشت كوير به‎همراه توپوگرافي قسمت‎هاي جنوبي و جنوب غربي، سبب تراكم بيشتر ريگزارها در اين قسمت هاي دشت كوير شده است. با استفاده از داده هاي حاصل از بادهاي مداري و نصف‎النهاري، جهت بادهاي تابستاني در قسمت‏هاي مختلف دشت كوير مشخص شد كه تا حدود زيادي با جهت گل‏بادهاي ايستگاه‏هاي هواشناسي و نوع مورفولوژي عوارض ماسه اي در تصاوير ماهواره‏اي منطبق است. مطالعه جهت بادهاي تابستاني، نشان‎دهنده وجود دو سامانه فشار متفاوت موثر در جهت‌گيري ريگزارهاي واقع در نيمه شرقي و غربي دشت كوير است.

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 32?). 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.