Wind erosion has played the major role in shaping Mu Us landscape. Although Mu Us Sand land is a hot spot, of research, the detail of wind erosion in Mu Us has been poorly understood. On the basis of observations in Mu Us Desert, we determine the threshold of wind velocity and present sand transport equations on bare and vegetated land. Furthermore, we discuss the quantitative relationship between vegetation cover and sand transport. We get a quite good understanding of the effect of vegetation on wind erosion.
Tropospheric column ozone data during 1979 to 1992 over the Tibetan Plateau and Solar flux F10. 7 index data at the same period, are used to evaluate the relationship between tropospheric ozone variation and solar flux change. It is shown that there exists a solar cycle changing trend in the tropospheric ozone at this region. The estimated changes in tropospheric and stratospheric and column total ozone over a solar cycle are representively 1. 31, 4. 97 and 6.628 Dobson Units (DU), or 4. 07%, 2. 04% and 2. 28% from solar minimum to solar maximum. This is quite different from that trend over tropic Pacific region discovered by Chandra et al. 1999. In the tropic Pacific region, a negative changing trend was found. There are at least two aspects should be put consideration in explain the difference. One is the different component of NO_x and water vapor in the background atmosphere over those two regions. The other is the continually stratosphere-troposphere exchange in the Tibetan Plateau may resulting in some ozone is sent to troposphere from stratosphere.
The protective role of vegetation in soil erosion by wind has been recognized by agriculturalists for some time. In practice, trees, shrubs and post-harvest residues have been widely used to stabilize sand against transport by wind erosion. However, little attention has been paid to some crucial aspects of vegetation protection against wind erosion in China, such as the quantitative relationship between vegetation cover and sand transport. In the past ten to twenty years, scientists have made great progress in this field. In this paper, relevant research articles associated with the protection of vegetation against soil erosion by wind are reviewed and present knowledge in this field is introduced. The progress of research on vegetation protection is classified into three aspects, theoretical basis, experimental observation and quantitative modeling. In the last part, research needs in China are discussed. In the first part, three theoretical avenues are discussed, including roughness concentration as a vegetation-describing variable instead of vegetation coverage, ineitial sublayer wind profile and shear stress partitioning on a vegetation covered surface. Vegetation coverage has long been used as a variable describing vegetation cover in research on soil erosion by wind. However, the roughness concentration based on the upwind projected area of vegetation cover is a much more suitable and convenient variable, which summarizes the geometry and spacing of roughness elements in a dimensionless manner. When the ground is covered by vegetation, wind velocity above the ground may be described using the logarithmic profile with a displacement height d and a new roughness length different from that of the bare ground. When the wind blows over a surface covered by vegetation, the total shear stress of the wind is then partitioned between the vegetation and the surface. The second part introduced the progress in experimental observation research. Some experiments suggest that aerodynamic roughness might be related to the height and roughness concentration of the vegetation cover. Other experiments measure the shear stress partitioning between the vegetation and the surface. In the third part, recent research on the quantitative models of vegetation protection on soil erosion by wind is introduced. Some researches have made great progress on the quantitative models simulating the relationship between vegetation cover and sand transport by wind. In the last part, situation of research on vegetation protection on soil erosion by wind in China is discussed, and some urgent research needs are outlined, including a complete study of the influence of vegetation on soil surface in wind erosion, choosing the suitable vegetation cover type in vegetation constructing projects, determing the effective vegetation coverage against soil erosion by wind, and the principles of vegetation construction. The aim of the present paper is to summarize the main progress of research on vegetation protection against soil erosion by wind and outline those aspects that urgently needed more attention and study according to the Chinese research situation and protective practices agaist soil erosion.
