呼伦贝尔沙质草原碟形风蚀坑表面气流及其意义

Geomorphological Significance of Air Flow over Saucer Blowout of the Hulun Buir Sandy Grassland

呼伦贝尔沙质草原风蚀坑发育于宽单峰中能风况环境,是该区主要风沙地貌类型。对碟形坑表面气流的观测结果显示,气流进入风蚀坑后,在入风口扩散,风速开始降低至坑底达到最低;在坑后缘出风口汇集形成急流,风速剧增至坑后积沙顶部风速达到最高值。风蚀坑后缘在风沙流的磨蚀作用下后退,风蚀坑顺风向扩展,同时此处较大的剪切风速和输沙率使大量来自坑内的沙物质沉积到坑后草地上呈扇状蔓延。呼伦贝尔沙质草原风蚀坑在来自西北、西和西南方向风的交替作用下,向东南、东和东北方向扩展而生成。随着风蚀坑深度和水平尺度的增加,最终可能沿强风能方向或合成输沙方向扩展成为大型的槽形坑。

Blowouts in the Hunlun Buir sandy grassland develop in a medium wind energy environment, and is the main type of Aeolian landscapes in this area. Saucer blowout is a specific phase in blowout development. The surface airflow dynamics and its relation with the geomorphological development of saucer blowouts are measured and analyzed in the paper. Measurements show that airflows diffuse in the wind entrance of blowouts, the wind speed gradually weaken to be the smallest at the bottom of blowouts; airflows converge into torrent at rear of blowouts, the wind speed increase sharply to be the highest at the top of accumulated sands. The back rim of blowouts retreat under airflow ablation, afterwards blowouts expand along the wind direction, simultaneously, a lot of sands are transported from blowouts to deposit on grassland behind depression, appearing fan shape. Being driven alternatively by winds from northwest, west and south- west, blowouts in the Hunlun Buir sandy grassland expand towards southeast, east and northeast directions respectively. Finally, blowouts develop into large trough ones along strong wind energy direction and resultant sand transporting direction.