Dust emission generated by wind erosion is a basic process before the transport and deposition of dust particles.Parameterization of dust emission flux is important for accurate simulation and prediction of dust events.Field observation and numerical simulation axe two approaches to understand the complex process of dust emission.Great progress has been made on the characteristics and mechanism of dust emission during dust storm events.This review introduces the major factors influencing dust emission and summarizes the calculation methods of several key parameters of dust emission,including the threshold friction velocity u_(*t),threshold wind speed U_t,streamwise saltation flux Q,and(vertical) dust emission flux F,from perspectives of both observation and parameterization.The paper also discusses the improvement,application,and validation of different dust emission schemes in dust models.Existing problems and future research directions are elaborated as well.
In this study, the effects of soil moisture on sand saltation and dust emission over the Horqin Sandy Land area are investigated, based on observations of three dust events in 2010. The minimum friction velocity initiating the motion of surface particles, namely, the threshold friction velocity, is estimated to be 0.34,0.40, and 0.50 m s-1under the very dry, dry, and wet soil conditions, respectively. In comparison with the observations during the dust events under the very dry and dry soil conditions, the dust emission flux during the wet event is smaller, but the saltation activities of sand particles(d 50 μm) are stronger. The size distributions of airborne dust particles(0.1 d 20 μm) show that concentrations of the finer dust particles(0.1 d 0.3 μm) have a secondary peak under dry soil conditions, while they are absent under wet soil conditions. This suggests that the surface soil particle size distribution can be changed by soil moisture. Under wet soil conditions, the particles appear to have a larger size, and hence more potential saltating particles are available. This explains the occurrence of stronger saltation processes observed under wet soil conditions.
In this paper, turbulent data obtained from the Damxung site during the Secondary Tibetan Plateau Science Experiment (TIPEX) in 1998 are used to study the characteristics of the turbulent spectra, turbulence transport, and the dissipation rates of turbulent kinetic energy, temperature variance, and humidity variance in the middle area of the Tibetan Plateau. The turbulent spectra of wind velocity, potential temperature, and humidity satisfy the-2/3 power law in the high frequency range. Horizontal transportation of heat and water vapor is negligible compared with vertical transportation under strong unstable conditions, and as the stability parameter z/L increases (where z is the observational height, and L is the Monin Obukhov length), horizontal transportation becomes dominant under near-neutral, neutral, and stable conditions. The non-dimensional temperature and humidity variances are 20% less than the temperature and humidity gradient variances. These deficits appear to increase as the absolute stability parameter increases. Moreover, the effects of turbulence transportation and pressure variance exist throughout the entire stability region.
