Measurement of saltation process over gobi and sand dunes in the Taklimakan desert, China, with newly developed sand particle counter

Abstract

The Japan‐Sino joint project, Aeolian Dust Experiment on Climate impact (ADEC), was initiated in April 2000 in order to understand the aeolian dust impact on climate via radiative forcing. As a part of the ADEC project, we have conducted field research in a sand dune and a gobi (i.e., a desert in which the soil surface consists of sand and pebbles with flat surfaces) in the south of the Taklimakan desert, China. The purpose of this study is to understand the wind erosion process and its relation to the meteorological and soil physical parameters. For this purpose, we measured the vertical profiles of wind speed, air temperature, and humidity as well as the other meteorological elements using an automatic weather station. A new sand particle counter (SPC) was newly developed to measure the saltation process. The SPC detects a signal change when a saltation particle passes through the slit between the laser beam transmitter and receiver. From this signal change, we can measure saltation particles from 30 to 667 μm diameter with 32 bin classes and particle numbers of each bin class every second. We have operated this SPC in the field, and it proved to be useful for the saltation process study when data corrections and calibration were properly made. During the observation period (1–21 April 2002), a total of eight dust events occurred; we analyzed two events: 5 April and 14 April cases. The results can be summarized as follows: (1) Total saltation fluxes in the 5 April case from 1223 to 1430 UT were 37.93 kg m−2 at 30 cm height and 43.71 kg m−2 at 20 cm height for the gobi site and 2.61 kg m−2 at 30 cm height for the dune site. (2) In the 14 April case, from 0327 to 0830 UT, the total saltation flux was 8.95 kg m−2 at 30 cm height for the gobi site. (3) Saltation flux at the gobi site in the 5 April case was more than 10 times larger than that of the sand dune, though the distance between the sites is 4 km. This is because the number of the parent soil particles around 80 μm at the gobi site was more than 10 times greater than that of the dune site. (4) Height dependency of saltation particle size and number was found in the gobi site; that is, the particle size distributions at the gobi sites in the 5 April case indicated that the number size distribution of the coarse particles, 117 to 554 μm, at 20 cm height was greater than that at 30 cm height. This size‐height dependency was reasonable from a physical point of view. However, present theory cannot explain this well.