VERTICAL DISTRIBUTION OF GRAIN-SIZE PARAMETERS OF DRIFTING PARTICLES DURING SAND STORMS IN THE TAKLAMAKAN DESERT,CENTRAL ASIA

The vertical distributions of grain-size parameters of drifting sand flux during sand storms in the Taklamakan Desert, Central Asia, were investigated through field observation and laboratory wind-tunnel tests. The results show that grain-size parameters of the drifting sands near the ground surface are similar to those of the source deposits. Fine and very fine sands in the flux layer near the ground surface (from zero to 20 cm high) comprise more than 85% of the sample's weight, with a mean diameter of 0.09 mm. The distributions of transported particles are mainly negatively skewed, with good sorting. The creep population consists of poorly sorted coarser particles. In the saltation layer, particle size becomes finer as a power function of height from 4 to 14 cm. Sorting in the saltation layer is good and improves as a logarithmic function of height. The higher the transport layer, the more negatively skewed the particle distribution becomes as a logarithmic function of height. It becomes more leptokurtic as a power function of height in the transport layer from zero to 12 cm high. Grain-size parameters change irregularly at heights above 14 cm. Regional differences in the vertical distribution of grain-size compositions are affected by source deposits, wind speeds, and transport rates, but source has more influence on the sorting of the drifting material than wind velocity.