偏西风作用下敦煌月牙泉金字塔沙山顶部风沙流初步观测研究

金字塔沙山丘体高大，形态复杂，坡面风沙动力过程实地观测困难，至今尚无坡面风沙流野外观测数据。通过新研制自动集沙仪，对偏西风作用下敦煌月牙泉北侧金字塔沙山顶部风沙流进行了实时观测，共观测8组近地表51.4 cm高度内输沙数据，各观测时段中2 m高度平均风速7.46～14.15 m·s^-1，各组观测时长18~95 min。结果表明：偏西风纵向气流作用下金字塔沙山风沙流结构与平坦地表一致，即输沙量随高度增加呈单一的指数规律递减，且风沙流主要在近地表30 cm高度内输移。风沙流结构特征值λ以大于1为主，且随风速增大而增大，表明金字塔沙山坡面过程主要表现为风蚀过程。偏西风作用下金字塔沙山风沙流中沙粒以细沙为主，平均粒径随高度增加而减小；沙山迎风坡沙粒从坡脚到沙脊线逐渐粗化，风蚀作用增强，细沙从而随风沙流搬运至沙山顶，对金字塔沙山多以细沙为主的格局形成起重要作用。

Aeolian Sediment Flux and Grain Size over the Top Area of A Star Dune near the Crescent Moon Spring of Dunhuang under Westerly Winds

The large volume and complex morphology of star dunes lead to difficulties in field observations of aeolian processes over their dune sides, and thus few studies of wind-blown sand over the star dune has been conducted. This paper focused on characteristics of aeolian sand flux profiles over the windward slopes of a star dune in north of the Crescent Moon Spring during westerly winds through a newly-developed sand trap, including 8 runs with duration 18-95 min and average wind speeds of 7.46-14.15 m.s^-1 at height of 2 m. Results revealed that sand flux profiles over the windward slopes of the star dune were similar to those over the flat sandy surface in the same area, that is, sand transport rates decreased exponentially with the increase of height. Sand transport over the star dune slopes was concentrated on the height of 20-30 cm. The characteristic values of the sand flux profile (λ) was mainly larger than 1,and increased with the average wind speed at the height of 2 m, so star slopes were eroded. The transported sands in the wind-blown sand were mainly composed of fine sands, and fine sands were transported to the area near the dune top, where deposited sands were mainly composed of fine sands.