Study On Optimization Of The Dust Model System And Quantitative Classification Of Dust Events In East Asia

Dust events, especially severe dust storm not only are disastrous weather with extreme harm in arid, semiarid region and its surrounding area, but also become an environmental problem which causes harm to the human being health and affects economic development. In this paper, on the basis of the physical mechanisms of sand and dust emissions by wind erosion the influences of different factors on sand and dust emissions have been studied by using the dust model system. The empirical relationship between visibility and PM₁₀ concentration is established by regression analysis of visibility and PM₁₀ concentration that were taken every 5 minutes at sixteen dust event's observation stations of northern China in springs. The prediction capability of numerical dust model is improved by optimizing dust concentration of initial field and estimating the surface soil moisture for dust model system. The difference in dust events classification in different countries in East Asia is analyzed. On the basis of TSP, PM₁₀ concentration and wind speed, a quantitative classification for dust events is proposed for East Asia. Consequently, a corresponding relation is established between results of dust model with observations. It is helpful for forecaster to using model results. The following is some conclusions:(1) The simulated results of the four schemes of sand and dust emissions of Shao(2001), Marticorena and Bergametti(1995), Shao(1996) , Lu and Shao(1999) are compared. It is found that the simulated results of Marticorena and Bergametti(1995), Shao(1996) are over the range of actual dust events observation, those of Lu and Shao(1999) are less than the range of observation, that of Shao(2001) is consistent with the range of observation. So the dust model system of Shao(2001) is preferably used to predict the dust events in China.(2) By analyzing the surface soil moisture and the initial field of dust concentration in previous dust model system, it can be seen that those variables is very different from the fact. Therefore, the surface soil moisture influencing wind erosion is estimated by precipitation, cloud, air temperature and wind speed. The dust and PM₁₀ concentration are estimated from visibility. After these corrections, 24-hour and 48-hour simulated results of dust events in intensity and spatial distributions are all improved, especially for 24-hour simulated results. When the dust events occurred in larger area, the prediction capability of improved dust model system is greatlypromoted by optimizing initial field of dust concentration.(3) More dust storms were reported in North Korea in contrast with itsneighboring regions of China and South Korea in springs. This shows that the represented intensity of the same dust events is different in different countries. In China and Japan, the TSP and PMio concentrations for severe dust storm and dust storm are higher than that in other countries, while the PMio and TSP concentrations for blowing dust and floating dust over the Indian Subcontinent are highest. The minimum of TSP concentration range for severe dust storm is in North Korea. The minimum of TSP concentration range for dust storm is in South Korea. The TSP concentration range of blowing dust in south of the Korea Peninsula and parts of the Tibet Plateau are lowest. The PMio concentration ranges of severe dust storm and dust storm in Korea Peninsula and Mongolia are lowest.(4) The proposed classification standards for dust events in East Asia have been put forward for the first time by comprehensive analysis and research, severe dust storm Ptsp> 6000ug m°, Ppmio> 5000ug m"3, v > 10m s"1;dust storm: 3000ug m"3< Ptsp < 6000|ig m3, 3000ug m"3 < pPMio < 5000ug m"3, 10m s"1 < v < 15m s"1;blowing dust: 900ug m"3 < pTsp < 3000ug m"3, 200uï¿¡ m"3 < pPMio< 2000p.g m"3, 5m s"1 < v < 10m s"1;and floating dust: 750ug m"3< pTsp< 1200ug m"3, 200ug m"3< pPMio< 600ug m'3, 2m s"1 < v < 5m s"1.(5) The sand and dust emissions by wind erosion under the La Nina phenomena and El Nino phenomena are analyzed by using the dust model system. The results are as follows: If the La Nina phenomena appears in equatorial eastern Pacific Ocean, the dust emission flux in Chinese mainland will obviously increase;if the El Nino phenomena appears in equatorial eastern Pacific Ocean, the opposite result will occure;variation range of the dust emission flux during the La Nina is exceeded that of El Nino. This is consistent with the statistical results.