固定沙丘风蚀坑风沙动力学观测研究

风蚀坑是固定沙丘活化的标志,也是沙漠化的首要环节。本文利用三杯风速仪、风向标及阶梯式集沙仪,对浑善达克沙地南缘固定沙丘风蚀坑的气流及输沙进行了观测。结果表明,气流进入风蚀坑后,经历了扩散减速—辐合加速—分离减速—逐渐恢复的过程。入风方向的微小变化、地形及植被导致风蚀坑气流结构、强度及输沙模式趋于复杂。与轴线平行（< 10°）的纵向气流使侵蚀坑内减速区西移,风速及输沙率由坑底向两侧壁及积沙区增加;与轴线斜交（≥ 10°）的气流使减速区东移,气流沿两侧壁向东加速及输沙。积沙区顶部的气流汇集与植被的作用使其加积增高。气流—形态相互作用使风蚀坑加深和纵向延伸并伴随侧向扩展。

Aeolian dynamical process of blowout on the fixed dune

Blowouts are the precursors to dune reactivation, which is the primary manifestation of desertification. Masts of three-cup anemometers, wind vanes, and sand traps were used to measure wind flows and sediment transport rates through a blowout developed on the fixed dune, which is located on the southern fringe of the Otingdag Sandy Land. Results demonstrate that after entering the blowout, airflow expanded and decelerated, reattached and accelerated, separated and suddenly decelerated, and gradually accelerated. The angle of incidence between the approaching wind and the blowout long-axis, local topography and vegetation significantly affected the airflow patterns and sediment transport rates. When winds approached from directions within 10° of the blowout axis, the deceleration zone moved westwards, airflow accelerated from the bottom of the blowout to the erosional walls and the depositional lobe; when the approach angles became oblique and equal or greater than 10° of the axis, the deceleration zone expanded eastwards, airflow accelerated and transported sediments to the east. Airflow reattachment and highly dense vegetation on the top of the depositional lobe captured and deposited considerable sediments, contributing to the increment of the height of the depositional lobe. The flow-form interactions within the study site gave rise to the deepening, elongating and widening of the blowout.