关键词: 塔克拉玛干沙漠, 线形沙丘, 动力学过程

Abstract: Linear dunes in the central Taklimakan Desert are mainly distributed in the interdunes of compound longitudinal sand ridges. With the exploration and exploitation of oil and natural gas, the oil highway and buildings which are located in the interdunes where linear dunes dominate, are being threatened seriously by the sands from linear dunes' elongation. The dynamic process is the crux of understanding the formation and development of linear dunes and can provide the theoretical found of engineering design for the prevention of sand hazards caused by linear dunes. According to field investigation, the linear dunes in central Taklimakan Desert average 400~500 m long, 3~10 m wide and 3~5 m high with the maximum length of mo re than 2 000 m. The average trend of linear dunes is N55°E. Meterological obse rvation shows that the prevailing wind in central Taklimakan Desert is ENE(N67.5°E), when crossing at the southeast side of linear dunes there is an oblique a ngle of 12.5° to the linear dunes. The secondary winds of relatively high frequency are NNE, NE on northwest side of linear dunes and E,ESE on southeast side. The annua l resultant wind direction is N67.7°E, which is almost the same as the directi on of the dominant wind(N67.5°E). But the variability of wind direction is pro minent: RDP/DP=0.58. The annual resultant drift direction(RDD) is 239.8°(N59.8°E), in dicating that the linear dunes in central Taklimakan Desert are typical longitud inal dunes according to their dynamic definition. Tunnel experiments imply that the de flected flow on the leeside almost constantly exists when the wind is oblique to a linear dune. And the deflected flow decreases with the increase of the acute incidence angles.Because of the deviation of air flow after it reaches the top o f linear dunes, lower wind velocity is observed above the upper leeside than that near the attachment. If air flow and resultant drift potential (RDP) are resolved into two sections which are parallel and perpendicular, respectively, to the dune crest, the parallel ones are both much more than the perpendicular ones because of low incidence angles between the wind direction and linear dunes' trend. Such air flow, therefore, causes the grains on both windward and lee sides moving along the crest direction, which will maintain th e longitudinal form of dunes. The RDP, however, gives reason why linear dunes elongate rapidly(about 10 m·a^-1) during the windy season. In contrast, the whole lateral migration of linear dunes in this area is not distinct probably because of the significant variability of wind direction which may has caused reverse lateral migration. But the local lateral migration above the dune base is frequently observed. Wind regime indicates that the formation of linear dunes in central Taklimakan Desert does not agree with the theory of bidirection wind. Several or more crescent dunes in alignment exist at the upwind ends of linear dunes, which may have suggested that the linear dunes in central Taklimakan Desert have closer relationships with barchan dunes in formation.This had been demonstrate d by Bagnold(1954).

Key words: Taklimakan Desert, Linear dunes, Dynamic process