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 are 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 Ut, 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.
[1]Dust emission generated by wind erosion is the largest source of tropospheric aerosols.The Gobi Desert in n...
Xiaolan Li and Hongsheng Zhang 1 Laboratory for Climate and Ocean-Atmosphere Studies,Department of Atmospheric and Oceanic Sciences,School of Physics,Peking University, Beijing,China. 2 Key Laboratory for Semi-Arid Climate Change of the Ministry of Education,Lanzhou University,Lanzhou,China.
In this study, the eff ects 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？1 under 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 fl ux 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 fi ner 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.
The measuring principle and development process of self-developed fast-response visibility meter was introduced,and the comparative test with FD12 visibility meter was carried out.Meanwhile,by using the observational data from automatic weather station from October 2004 to March 2005,the evolution characteristics of visibility and its relationship with relative humidity,wind speed and temperature in autumn and winter in northern Beijing were discussed.The results showed that self-developed visibility meter could reflect the variation trend of visibility,with good comparison results,and could be used to measure visibility,while its frequency response was over 1 Hz,meeting the fast-response requirement of atmospheric visibility measurement and relevant detection.In northern Beijing,atmospheric visibility was significantly negatively correlated with relative humidity but significantly positively correlated with wind speed,while temperature could affect visibility indirectly by changing relative humidity and atmospheric stability.Gale and heavy fog had important effects on visibility.
[Objective] The research aimed to review the analysis and research on the physicochemical characteristic observation aspect of fog. [Method] To understand the roles of fog microphysical characteristic and chemical reaction on the formation, dissipation, development of fog, the interaction between the microphysical structure, chemical characteristic of fog and the aerosol in the environment, the analysis and research on the micro-physicochemical observation aspect of fog were mainly introduced here. We also put forward that the field still needed the deep research content. [Result] The observation and research on the micro-physicochemical characteristics of fog could reveal the mechanisms of fog formation, dissipation, development from the microphysical components and the reaction of chemical composition. The previous researches focused on the concentration of micro-fog droplet, the particle size of fog droplet, the liquid water content in the fog, the particle concentration, size, chemical component and reaction of aerosol. It included the evolution and interaction between the microscopic quantities in the fog, the relationship between the microscopic quantity and the visibility. As the improvements of observation experiment instruments and sampling method, it recognized that the fog in the polluted environment condition and the clean air had the obvious difference whether in the microphysical characteristic or the chemical component. The particle concentration, chemical component and liquid water content of fog were all depended on the fog particle size. The interaction between the radiation, turbulent flux and the micro-physical characteristics of fog, the vertical structure of microphysics in the fog, the interaction between the chemical components, the relationship between the microphysical quantity and the macro-physical quantity (such as the visibility), the precision of experimental instrument, etc. needed the further research. [Conclusion] The research provided the comprehensive knowledge for the characte
