Field Observation Evidence for Kink Points in the Vertical Kinetic Energy Flux Profiles of Wind-blown Sand over Gobi and Its Significance
Description
We have performed comprehensive measurements of the vertical profiles of particle counts and kinetic energy for wind-blown sand over gobi. In the three measurement sites, four aeolian transport events were measured, two of which were measured in R1 (20180501R1 and 20180504R1; 39°8.062′N, 88°59.967′E) and one in each of R2 (20190514R2; 42°18.250′N, 94°1.483′E) and R3 (20190523R3; 43°6.983′N, 91°9.533′E). The vertical profiles of the particle count and KE flux were measured by vertical arrays of piezoelectric impact sensors (H11-LIN 10×, Sensit), and the saltation mass flux profiles over gobi were measured by vertical arrays of Big Spring Number Eight (BSNE) traps. In R1, a vertical array of five piezoelectric impact sensors was deployed at heights of 0.05, 0.12, 0.38, 0.80, and 1.38 m (geometric mean) above the ground with a measurement frequency of 1 Hz. Seven sand traps were deployed at mid-inlet heights of 0.025, 0.175, 0.285, 0.585, 1.16, 1.79, and 3.00 m. Wind profiles were observed by four HOBO U21 anemometers at heights of 0.20, 0.80, 2.00, and 3.00 m with a measurement time interval of 1 min, located approximately 20 m east of the saltation observation site. In R2 and R3, seven piezoelectric impact sensors were deployed at multiple heights, and the respective deployment heights were 0.05, 0.17, 0.31, 0.54, 1.00, 1.47, and 2.14 m above the ground in R2 (Figure 1e) and 0.05, 0.22, 0.59, 1.16, 2.47, 4.00, and 6.00 m above the ground in R3. The measurement frequency was 1 Hz. Seven BSNE traps were deployed at heights of 0.025, 0.20, 0.285, 0.31, 0.72, 1.30, 2.09 and 3.30 m in R2, and those in R3 were situated in a wind-blown sand measurement tower with 16 traps at heights of 0.025, 0.125, 0.275, 0.575, 0.875, 1.175, 1.575, 1.975, 2.475, 2.975, 3.475, 3.975, 4.975, 5.975, 6.975, and 8.975 m above the ground (Figure 1f). The wind profiles in R2 were measured by three HOBO U21 anemometers at heights of 0.20, 0.50, and 2.00 m with a measurement time interval of 1 min, located approximately 10 m south of the saltation observation site. In R3, the wind speed and direction were measured by a Gill 2-D sonic Windsonic at a height of 2 m with a time interval of 10 min, located approximately 10 m north of the saltation measurement site. The results show that unlike the exponential decrease in the particle count flux with height, the KE flux profile curve was nonmonotonic and could be well fitted by a Pearson VII function. The height where the maximum KE flux density occurred (kink points) ranged from 0.09 to 0.15 m above the ground. In addition, the nonmonotonic KE flux profiles primarily emerged during periods of strong transport and were mainly caused by large saltating sand particles due to their high KE as they rebounded from the grain-bed collision.