沙质草地碟形风蚀坑形态气流相互作用

 呼伦贝尔沙质草地碟形风蚀坑长轴走向呈WNW-ESE。野外观测结果表明,风向与碟形风蚀坑长轴走向关系决定了风蚀坑内部的气流模式,右斜交与垂直气流促使风蚀坑横向扩展与深挖,平行与左斜交气流有利于侵蚀区内部沙物质的向外输送并导致风蚀坑沿长轴向延伸。右斜交及垂向气流在碟形坑南缘产生顺时针向的垂直轴涡流,而平行与左斜交向气流在西北缘产生逆时针向的垂直轴涡流。沿长轴向,气流进入风蚀坑边缘发生分离减速,在风蚀坑底部重新附着,沿出风段坡面开始加速上升至坑后沙丘顶部,在坑后沙丘背风坡气流发生扩散减速。在横断面或弧形断面气流以单增或单减的形式存在。观测期间风蚀坑总体上以堆积作用为主,区域风能大小决定了蚀积作用强弱,而输沙方向与风蚀坑长轴向夹角决定蚀积空间分布格局。

Interaction between Airflow and Shape of Saucer Blowout in Sandy Grassland

The long axis direction of saucer blowouts is WNW-ESE in Hulun Buir sandy grassland. According to the angle between wind direction and the blowout's long axis direction, airflows could be classified as perpendicular flow, left oblique flow, right oblique flow and axis-parallel flow. Field observations show that right oblique flow and perpendicular flow result in blowout's lateral expansion and deepening; left oblique flow and axis-parallel flow lead to sand outward transportation and blowout extending longitudinally. Right oblique flow and perpendicular flow can form clockwise perpendicular whirl in south margin of the saucer blowout; axis-parallel flow and left oblique flow can form anticlockwise perpendicular whirl in its northwest margin. Along the long axis direction of the saucer blowout, air flow separates and decelerates when it approaches the blowout's margin, then re-attaches at the bottom of the blowout, and then accelerates and climbs along the outlet slope till the top of the dune, lastly diffuses and decelerates in the leeward of the dune behind the saucer blowout. In cross section or arc section of the saucer blowout, airflow monotonicly increases or reduces. Deposition process principally dominated the blowout during observation period. The intensity of erosion and deposition is determined by resultant sand-transporting potential, while the angle between resultant sand-transporting potential direction and the long axis direction determines the spatial distribution pattern of erosion and deposition.