Micrometeorological Characteristics during Severe Dust Storms in Spring of the Beijing Area in 2010

Based on the PM10 concentration observations from Peking University and the profiles of meteorological parameters and turbulence measurements from the 325-m meteorological tower operated by the Institute of Atmospheric Physics, Chinese Academy of Sciences, the variations in micrometeorological and dust parameters and the characteristics of turbulent transfer were analyzed during two severe dust storms occurring during 20-22 March 2010, which can provide references to studies of dust transport discipline and micrometeorological characteristics during severe dust storms in the Beijing area. The results indicated that temperature at different levels increased at first and then decreased during the severe dust storms, however, air pressure and relative humidity oppositely evolved. As the severe dust storms broke out, wind speed at higher levels increased earlier than that at lower levels, and wind shear became intense. The maximum values of PM10 concentration almost coincided with those of wind speed. Considerable increases were shown in downward turbulent momentum fluxes, upward turbulent sensible heat fluxes, and turbulent kinetic energy at different levels. Comparing with the clear day on 21 March, turbulent momentum fluxes enhanced and helped with dust transport. Because of the cold front system accompanying with dust storms, horizontal sensible heat fluxes apparently became larger, and vertical sensible heat fluxes increased at night due to the breakdown of inversion layer, but dropped at daytime owing to the minished temperature vertical gradient. Horizontal turbulent kinetic energy accounted for the largest proportion of turbulent kinetic energy, and vertical turbulent kinetic energy took up only 10%-25% of horizontal turbulent kinetic energy.