The Mechanism of Dust Entrainment under Strong Wind with Gustiness

In East Asia the large range dust storm almost occur after cold front passage in spring. Here, we try to find the mechanism of dust entrainment by the gust wind by analyzing observation data and numerical simulation result. First, the ultra-sonic anemometer-thermometer data during the dust storm periods in 2000-2004 have been analyzed. It is revealed that the air motion during dust storm can be divided into three parts, the turbulent small eddies, the gust wind, and large scale basic flow. In the lower part of atmospheric boundary layer, the descending component of basic flow suppresses the dust particles keeping them within the bottom layers. But the gust wind has coherent structure, and due to the gust wind not turbulence, the dust can entrain from lower to upper levels. Second, we use Lagrangian Stochastic Model to simulate the particle trajectory during dust storm period. The wind condition comes from the observation wind profiles. It includes basic flow profile, gust wind profile and turbulent intensity. When there are only turbulent fluctuations, particles have random trajectories and can reach 250m height. Once adding gust wind, particles are carried in the air stream and have the potential to be transported to great heights (higher than 500m) and over great distances. But if no gust wind and adding descending component of basic flow, particles are only accumulated in the bottom of layer. The simulation result shows that the mechanism of dust entrainment during strong wind is mainly due to the gust wind.