腾格里沙漠东南缘沙丘表面气流与坡面形态的关系

Near surface Airflow and Slop Morphology of Dunes in Southeastern Tengger Desert

对腾格里沙漠东南缘格状沙丘主、副梁和新月形沙丘断面风速的野外观测结果表明，迎风坡风速放大率、背风坡气流的方向和强度随区域气流、坡面形态而不同。迎风坡风速放大率对沙丘形态的作用在于增加丘顶区域的输沙率和活动性；背风坡气流不仅影响沙丘形态而且控制沙丘动力学过程。在横向气流条件下，风速放大率使沙丘迎风坡随区域气流强度的增加变长变缓，背风坡受分离流控制使沙丘迁移；在双向－斜向气流条件下，沙丘丘顶处于侵蚀亚环境而两坡变陡变短，背风坡受附着偏向流控制使沙丘纵向延伸。

Field measurement of airflow associated with slop morphology was made on the crescentic dunes and network dunes in southeastern Tenggr Desert in order to understand the general dynamics and morphology of sand dunes. It was found that there existed close relationship between dune morphology and wind flow. Wind velocity increased up the stoss slops and decreased down the lee slops and the changes varied with the primary wind direction and magnitude, and slop morphology. The amplification of wind velocity on windward slops ranged between 1.06￣1.95, and changed with both the primary wind direction and the slop morphology. In addition, when the primary wind direction was perpendicular to dunes there existed significant influences of the wind velocity at windward slops foot and dune height on velocity amplification. The main effect of the velocity amplification up windward slop was to increase the transport rate and the activity of sand at dunes crest zone. Therefore, the development of windward slop tends to be gentle and long with regional wind velocity increasing under transverse flow condition. Both sides of a dune become short and steep under bidirection-oblique flow condition. The lee side airflow was more complex than that on the windward side. The wind speed at leeward side is a log function of the cosine value of incidence angle. Lower leeward airflow speed (20%￣40% of crest speed) always occurred on steeper slops due to the flow separation in transverse flow condition, while higher speed wind flow (up to 92% of crest speed) essentially occurred on the gentle slops because of flow reattachment and(or) deflection in oblique flow condition. The lee side airflow not only controlled dune morphology but also influenced dune dynamics. Consequently, the dunes were advanced by erosion on the windward slop and deposition on the slip face in transverse flow condition. Sand transport and erosion took place on both windward and lee flank, and lead to dune elongation along their axis in oblique flow condition.