中文摘要：

气流结构是控制沙堆形态发育及演变的重要因子．用EC9．1型风杯风速计及风向标观测分析库布齐沙漠平坦薄层覆沙地上单个独立灌丛沙堆周围0．3m高处气流的水平变化及4m高度内的风速廓线，总结出单个独立油蒿灌丛沙堆的气流结构具有如下特征：在0．3m高度上，气流流速自积沙体迎风坡脚向两侧及背风侧呈先减后增的水平变化特征，背风坡脚的风速降至最低；在沙堆顺风向中轴线上，沙堆迎、背风侧附近的风速廓线分为二层，2H（灌丛沙堆总高度）以下为偏离对数分布的下凹型曲线，自下而上风速呈先减后增趋势，不透风积沙体与具疏透性的灌丛过渡高度处的风速最小，可能因过渡区存在反射流和涡流所致，2H以上符合对数分布规律，说明油蒿灌丛沙堆对气流的最大干扰高度不超过其总高度的2倍．全通透性型灌丛因积沙过程逐步转变为下密上疏型结构的灌丛沙堆，使得灌丛背风侧气流减速区长度迅速缩短，是拖着长尾的风影沙堆向椭圆形或近圆形灌丛沙堆演变的关键．

英文摘要：

Airflow profile is a key factor to control morphological development and evolution of nebkha dunes. EC9-1 cup anemometers and wind direction vanes were used to measure the wind speed and direction at 0.3m height and to measure velocity profiles at 4m height above thesurface. At 0.3m height, the velocity decreased along windward rim, two sides and leeward rim of the nebkha dune and the lowest velocity exsits at leeward rim. On axis of the nebkha dune, velocity profiles were divided into two layers. One layer was below the height of 2H（ H indicates the nebkha height） ,and in this layer the velocity profile was down concave curve with a non- logarithm distribution and velocity decreased first and turned to increase away from the surface. The lowest velocity existed at the transition zone between the nonporous dune and the porous nebkha as a result of contrajet and vortex. The other layer was between 2H to 4m,in which the velocity profile showed a logarithm distribution. This indicated that the maximum disturbed height was not beyond the double height of the nebkha dune. The porous nebkha shrub gradually shrub of important dune. changed to the nebkha dune composed with nonporous dune of lower part and porous upper part. As a result, the length of the to control evolution of a shadow dune with deceleration zone shortens fast, which is a long tail to ellipse or roundness nebkha