简单横向沙丘表面物质组成、气流分布及其在动力学过程中的意义

Airflow and Particle-Size Distributions and Their Significance on the Dynamic Process of a Simple Transverse Dune

对简单横向沙丘的形态特征、气流、表面以及被输移的沙物质组成的观测和分析表明 ,沙丘形态特征和表面物质组成的分异是导致沙物质在迎风坡坡脚不能沉积并向下风向输送的主要原因。对沙丘背风坡气流观测表明 ,在沙丘背风坡贴近地面的一定高度气流仍能保持一定的强度 ,其输沙方向与沙丘走向近似于垂直 ,并有相当强的输沙能力 ,但其作用被限制在背风坡范围内 ,这对保持沙丘形态有重要的作用。在野外风沙观测中气流的湍流和波动被忽略 ,平均风速并不能完全反映野外气流的性质。在低 -中强度风沙活动过程中 ,被输送的沙物质的粒度组成与下垫面物质有明显的差异 ,被输送沙物质的平均粒径小于下垫面沙平均粒径 ,输沙过程是一典型的随机过程。特定区域内 ,一定粒径范围内的沙物质不断被堆积而形成沙丘 ,经过一系列的动力学过程 。

Measurements of dune morphology,airflow and grain size of sands on a simple transverse dune showed that the variations of grain size and dune morphology were the main cause for the sands being transported from the upwind towards lee side of dune.At the lee side of dune,near the dune surface the stress of airflow did not decrease much with a direction vertical to dune trend,which have a great significance on the development of the dune.The mean velocity could not indicate the characteristics of airflow despite that the turbulent and fluctuation of airflow were ignored in field measurement.There were some variations on grain size of sands of dune surface and that being transported,which the mean grain size of being transported is smaller than that at the surface along the stoss side of dune.Within some scope the particles were accumulated to form the dune.After a series of dynamic process,the sketch map o the dunes were developed in the region.