北京两次重污染沙尘天气成因及动力传输特征的对比研究

Comparison of Causes and Dynamic Transport Characteristics of Two Heavy Pollution and Sand-Dust Weathers in Beijing

应用气象、空气质量和ERA-Interim再分析资料,结合HYSPLIT后向轨迹模型和地理信息,对比分析了2018年北京两次重污染沙尘天气的成因、传输特征及影响要素等。结果表明:两次过程的沙尘源地均为蒙古国,但3月28日沙尘天气由蒙古气旋引发,传输出现折向,以东北和偏东两条路径输送入京,5月28日沙尘受低涡和发展的低压冷锋影响,为典型的西北传输路径;高空的引导气流与低层冷空气的强度以及地形是导致沙尘传输出现显著差异的主要影响因素;高空为偏西气流,低层冷平流较弱,受到山脉的阻挡,沙尘气团东移至地势较低的区域后,在气压梯度力的驱动下传输方向发生转折,以偏东路径绕流进入北京;高空的偏北气流和低层冷平流较强,沙尘气团可直接翻越山脉从西北路径入京,沙尘粒子的运移高度相对较高。

Causes,transport characteristics and influencing factors of two heavy pollution and sand-dust weathers in Beijing in 2018 were compared and analyzed by using the meteorology data,air quality data and ERA-Interim reanalysis data,combining with the HYSPLIT backward trajectory model and local geographic information.The results show that sand-dust sources areas of the two events both are located in Mongolia.The Mongolia Cyclone initiated the sand-dust weather on March 28.Sand-dust transportation deflected and invaded Beijing from northeast and east.The event on May 28 was initiated by a vortex and developing cold front,with a typical northwest transportation path.Steering airflow at high level,cold air intensity at low level and topography are major factors inducing significant difference among sand-dust transportation characteristics.Affected by the high-level westerly airflow,low-level weak cold advection and mountain barriers,sand-dust air mass moved eastward to lower regions.Driven by air pressure gradient force,its transportation direction turned and then approached Beijing from eastern path.While the high-level northerly airflow and the low level cold advection were stronger,sand-dust air masses could directly climb over the mountains and invade Beijing from northwest path,with a higher moving level of sand-dust particles.