干旱区生态环境知识资源中心(Arid): Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect

Arid

DOI	10.1029/2020JF005913
	Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect
	Gao, Xin; Narteau, Clement; Gadal, Cyril
通讯作者	Gao, X (corresponding author), Chinese Acad Sci, Xinjiang Inst Ecol & Geog, State Key Lab Desert & Oasis Ecol, Urumqi, Xinjiang, Peoples R China. ; Gao, X (corresponding author), Univ Chinese Acad Sci, Beijing, Peoples R China.
来源期刊	JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
ISSN	2169-9003
EISSN	2169-9011
出版年	2021
卷号	126 期号:5
英文摘要	We study the morphodynamics of reversing dunes on the gravel deposits of the alluvial fan of the Molcha river at the border between the Tibetan Plateau and the Taklamakan Desert. Independent sets of wind data show that this area of low sand availability is exposed to two prevailing winds from opposite directions and of different strengths. The predicted resultant transport direction of sand particles is westward. Nevertheless, satellite observations combined with field measurements and ground-penetrating radar surveys reveal that isolated dunes a few meters high migrate eastward. This apparent dune migration paradox is resolved using numerical and analytical models that take into account the speed-up effect and the continuous change in dune shape after each wind reversal. When a newly established wind hits what was before the steeper lee slope of the dune, the sand flux at the crest abruptly increases before relaxing back to a constant value as the crest migrates downwind and as the dune reaches a new steady shape. Integrated over the entire wind cycle, we find that this non-linear behavior causes reversing dunes to migrate against the resultant transport direction. This migration reflects the difference in dune slope seen by irregular storm events blowing to the east and the westward wind of the daily cycle. Thus, we explore the impact of extreme events on dune morphodynamics and examine new aspects of the permanent feedback between dune topography and wind speed. We conclude that transient behaviors associated with crest reversals contribute to the observed diversity of dune patterns, even within the same area for dunes of different sizes. Plain Language Summary The wind accelerates when it is deflected over a dune so that the sand flux at the crest is several times greater than on a flat sand bed far from any topography. This speedup effect varies as the steepness of the dune slopes exposed to the wind. Here we show that, in zones of frequent wind reversals, the speed-up effect can cause the dunes to migrate against the transport direction of windblown sand particles. This apparent dune migration paradox requires specific conditions which are met in the study area, a large (8,000 km2) alluvial fan at the margin between the Tibetan Plateau and the Taklamakan Desert. First, it is an area of low sand availability and the dunes that develop on the gravel deposits of the alluvial fan do not exceed a few meters in height. Second, this area is submitted to two opposite winds with different strengths. Westward winds are weak but occur daily, while eastward winds are associated with storm events. Since the infrequent storm winds always blow over a dune that is regularly smoothed by daily winds from the opposite direction, they produce much greater sand flux at the crest of the so-called reversing dunes, which can then migrate against the sand flow path. This singular behavior governed by the permanent feedback between airflow and dune topography illustrates the critical role of extreme events in sediment transport dynamics.
英文关键词	crest reversals dune migration resultant drift direction reversing dunes speed-up wind reversals
类型	Article
语种	英语
收录类别	SCI-E
WOS记录号	WOS:000655231000011
WOS关键词	AIR-FLOW ; SEDIMENT TRANSPORT ; OBLIQUE DUNES ; WIND ; DYNAMICS ; ORIENTATION ; SALTATION ; STORMS ; MECHANISMS ; MORPHOLOGY
WOS类目	Geosciences, Multidisciplinary
WOS研究方向	Geology
来源机构	中国科学院新疆生态与地理研究所
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/350845
作者单位	[Gao, Xin] Chinese Acad Sci, Xinjiang Inst Ecol & Geog, State Key Lab Desert & Oasis Ecol, Urumqi, Xinjiang, Peoples R China; [Gao, Xin] Univ Chinese Acad Sci, Beijing, Peoples R China; [Narteau, Clement; Gadal, Cyril] Univ Paris, Inst Phys Globe Paris, CNRS, Paris, France
推荐引用方式 GB/T 7714	Gao, Xin,Narteau, Clement,Gadal, Cyril. Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect[J]. 中国科学院新疆生态与地理研究所,2021,126(5).
APA	Gao, Xin,Narteau, Clement,&Gadal, Cyril.(2021).Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect.JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE,126(5).
MLA	Gao, Xin,et al."Migration of Reversing Dunes Against the Sand Flow Path as a Singular Expression of the Speed-Up Effect".JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE 126.5(2021).