Influences of Vorticity and Atmospheric Boundary Layer upon Duststorm Generation and its Transportation

Duststorm, one of severe meteorological phenomena under strong winds blowing a great amount of sand was investigated from March 19 through 31, 2001. Previous research results have not given us the detail information on the evolution process of the duststorm and its vertical dispersion and the driving mechanism of the high pollutant concentration in the local area, regarding atmospheric boundary layer. Firstly, the relationship of baroclinic potential vorticity to the generation of duststom and its transportation, using three-dimensional nonhydrostatic model-MM5 and secondary, the reason of the sudden high concentration of aerosol in the local area were investigated, considering the meteorological influences upon the atmospheric boundary layer.

Near the area of the maximum negative geopotential height tendency at the 500 mb level, the area of maximum negative vorticity which induces the strong upward motion of air coincides the area of the duststorm generation in the inner Mongolia under the 30% relative humidity and wind speed over 7 m/s and the dust transportation always follows the negative vorticty area in the downwind side. The region of duststorm generation (maximum negative vorticity area) is the same region of the unstable atmospheric layer (negative potential vorticity (PV) value) near the ground surface in the vertical distribution of baroclinic PV, with a function of daibatic heating and frictional terms with respect to time. Air parcels (dust) for day are uplifted to about 700 mb level (about 3 km), where potential temperature gradient with pressure is zero and above 700 mb level, there is stable upper atmosphere influenced by the stratosphere. Convective boundary layer (CBL; negative PV value-PVU < 0) exists in less or more than 1 km and initially dust particle floats from the ground surface to the mixed layer (ML) of about 1.5 km above the CBL and it remains inside the ML. Westerly wind drives the particles to the downwind side.

At night, a shallow stable boundary layer (or surface inversion layer; big positive PV value) is developed near the ground surface and the particles inside the stable layer merge to the ground surface and move downwind side. The dust particles in the ML still move downwind side by wind and their dry deposition near the top of stable layer into the surface may occur. Stable layer near surface also forms for day and the dust particles merge into this stable layer, resulting in its high concentration in the local area.