北京市一次大雾过程边界层结构的模拟研究

NUMERICAL SIMULATION ON THE BOUNDARY LAYER STRUCTURE DURING A HEAVY FOG PROCESS OVER BEIJING METROPOLITAN AREA

利用一个包括土壤 植被 大气相互作用的一维边界层模式 ,对 1999年 11月发生在北京的一次大雾过程的边界层特征进行了数值模拟。通过与相应时段边界层观测资料的对比表明 ,模式能较好地模拟出雾的大气边界层结构特征 ,以及雾的发生、消散时间和持续过程。由于模式中包括了辐射和平流物理过程 ,因此 ,模拟结果进一步证实相应的雾属于平流辐射雾。另外 ,对模式模拟结果的不足之处和可能原因也进行了分析。

A simulation study of a heavy fog process over Beijing metropolitan area in November,1999, was conducted by use of a 1-D boundary layer model considering the soil-plant-atmosphere interaction with high vertical resolution. Comparative analysis between the simulation results and the corresponding field observation data, for the heavy fog lasting from 21:00, November 22 to 09:00, November 23, shows that the characteristics of the boundary layer structure associated with the fog can be reproduced by the model basically, as well as the occurrence, dissipation and sustainable time. The results also reveal some common features for the heavy fog, for example, the temperature is almost the same in vertical in fog, and the inversion is over the top of the fog, where the relative humidity is decreasing very rapid vertically, a relative maximum wind velocity appears whereas the wind speed is small in fog, and there exists the greater gradient for most physical variables. Further more, the results suggest that the fog was caused jointly by advection and radiation processes since those processes were included in the model. It ought to be pointed out that there are some limitations in the fog simulation, since the aerosol effect and the collision between the cloud particles were not considered in the model, as well as the radiation effects of rain droplet, water vapor and CO 2, and the dynamic forcing is unchanged in simulation period, which causes the discrepancies between the simulation results and the observation, especially with the much denser isograms for temperature, relative humidity, and so on, which should be improved in our future research.