腾格里沙漠东南缘格状沙丘表面气流及其地貌学意义

对腾格里沙漠东南缘沙丘形态与区域气流的分析表明,格状沙丘发育在双向低风能环境。沙丘表面气流及沉积过程的观测结果,主梁长期处在横向气流环境,其形态主要受背风坡分离气流控制,并以迎风坡侵蚀、背风坡净堆积形式顺主风向迁移。副梁处在双向-斜向气流环境,背风坡的附体偏向气流控制其形态和动力学过程,而且其强度是原始风入射角余弦的对数函数。在斜向风作用下,副梁迎风坡侵蚀的同时,背风坡中下部也发生沙粒的纵向输移且堆积于主梁背风坡,从而导致副梁沿年合成输沙方向延伸。由此认为,格状沙丘的主梁形成于主风-西北风的作用,而副梁是在主梁基础上并在主风和次风-东北风的交替作用下形成的;其形态动力学类型应属纵向沙丘置于横向沙丘之上一种复杂型沙丘。

Geomorphological Significance of Air Llow over Reticulate Dunes of the Southeastern Tengger Desert

Reticulate dunes are more common in the world desert but less understood.The reticulate dunes in the southeastern Tengger Desert are composed of SW-NE trending main ridges and the secondary ridges nearly perpendicular to the main one.Field measurements were made on the reticulate dunes in order to understand their morphology and dynamics.It is found that the dunes develope in bi-directional low energy wind regime.The morphology of the main ridges is mainly controlled by lee face separated flow and thus the ridges are advanced by erosion on the windward slop and deposition on the slip face in the conditions of transverse flow.The secondary ridges are in the oblique flow conditions,the lee side's attached and deflected secondary flow controls its morphology and dynamic processes.It results in sand transportation and erosion taking place on both windward flank and lee flank,and thus leads to elongation of the secondary ridges.It is also found that the magnitude of deflected flow is in a log function with the incident angle of primary wind.Therefore,the main ridges of reticulate dunes are formed by the dominant northwesterly wind,whereas the secondary are developed on the main ridges by a seasonally alternation of the dominant northwesterly wind and sub-dominant northeasterly wind.As for its dynamic morphology,the reticulate dune in the studied area is a complex that transverse dune is superimposed by longitudinal one.