影响北京的两次沙尘过程传输特征对比分析

2017年5月4-5日和2015年3月28-30日两次影响北京的沙尘天气均包含外来输送及沙尘回流过程。采用常规气象观测资料、大气成分资料、CALIPSO卫星监测及风廓线雷达数据等，对两次过程中的气象要素变化、传输轨迹、天气学条件、边界层特征等进行分析。结果表明：两次过程均由蒙古气旋引起，远距离传输过程中经沙源地传输的沙尘气溶胶可被抬升至700 hPa以上高度，主要传输层位于对流层中低层；高空急流强度、入口区位置及次级环流的结构对沙尘传输及影响区域有重要指示意义；沙尘回流主要受大气中低层偏南风输送带的影响，主要传输高度为1 km以下的低层大气，北京与回流上游城市PM₁₀浓度变化的时间滞后性与前期沙尘天气是否得到彻底清除有关。

Comparative Analysis of Transport Characteristics of Two Dust Events Affecting Beijing

The two dust events affecting Beijing on 4-5, May, 2017 and 28-30, March, 2015 included both long range transport and dust backflow. The variation of meteorological elements, transmission trajectories, weather conditions and boundary layer characteristics of the two events were analyzed by using conventional meteorological observation data, atmospheric composition data, CALIPSO satellite monitoring and wind profile radar data. It was found that both events were caused by Mongolian cyclone. The dust aerosol transported through sand source during long range transport can be raised to a height above 700 hPa, and the main transport layer was located in the middle and lower troposphere. High-altitude jet stream intensity, inlet zone location and the structure of the secondary circulation showed important indications for the dust transport. The dust backflow was mainly affected by the low-level southerly wind belt, and boundary layer below 1 km was the main transport layer. The time lag of PM₁₀ concentration variation between Beijing and upstream cities was determined by whether the dust weather had been completely removed previously.