华北平原一次大雾天气过程的数值模拟

Numerical Simulation of a Dense Fog over North China Plain

应用非静力平衡中尺度模式MM5V3,模拟分析了2005年11月19—21日发生在华北平原的一次大雾天气过程。结果表明,本次大雾是发生在相对稳定的大气环流背景下的辐射雾。模拟的天气形势与实况基本一致,模拟雾在范围、强度、生消时间等方面基本反映了实际大雾的生消变化规律。近地层逆温的维持和充沛的水汽条件对雾层长时间维持起着重要作用。诊断分析表明,大雾维持期间,雾区近地面层处在弱的水汽辐合区;900 hPa以上为辐散区和负涡度区,整层大气中下沉运动占主导,大规模的下沉辐散运动有利于中低层大气增温,与近地层的辐射降温相配合,有助于边界层内形成逆温;冷暖平流的作用也有助于逆温形成;地面和大气的长波辐射冷却,是最主要的降温因子;太阳短波辐射是导致大雾减轻及日变化的主要原因。

Based on T213 data and conventional observation data,a dense fog occurring in North China plain between 19th-21st, November,2005 was simulated by using mesoscale model MM5. Results show that the heavy fog is a radiation fog occurring in stable synoptic situation. The location, intensity, formation and dissipation of the simulated fog are in accordance with the real situation. The inversion layer and abundant moisture play an important role in the maintenance of the fog. Diagnostic analysis indicate that：the fog area locates in weak vapour convergence area;the descending movement accaused by the divergence and negative vorticity above 900 hPa contributes to the formation of the inversion layer ; the cold advection is also favourable for the formation of the inversion layer; the long wave radiation cooling is a predominant factor for tempereture decresing ; and the short wave radiation plays an important role in the fog dissipation and diurnal variations of the fog.