濮阳一次持续性雾霾天气的阶段性特征和维持机制

Stage Characteristics and Maintenance Mechanism of a Persistent Fog-Haze Process in Puyang

2018年11月23日至12月3日,华北平原出现了一次较长时间的雾霾天气。利用常规气象观测资料、NCEP/NCAR再分析资料和污染物浓度资料,以河南省濮阳市为例,对此过程的大尺度环流背景场、边界层内气象要素特征、动力因素和污染状况等进行综合分析,分3个阶段探讨此过程形成的原因和维持机制。结果表明:(1)雾霾发生在高空纬向环流背景下,华北处于高压脊前西北气流中,频繁受下滑短波槽影响。(2)冷空气活动偏弱,中低层维持暖脊控制,使边界层内出现较强逆温,制约低层水汽和污染物的垂直扩散。(3)地面处于均压场或锋后弱冷高压控制,弱风条件不利于污染物的水平扩散。(4)前期大雾形成时,强逆温层在900 hPa以下的贴地高度,能见度很低,污染严重;中期霾严重时,较强逆温层上移至900—850 hPa,并出现双层逆温,能见度虽较好,污染仍然严重;后期的雾霾主要由高湿度环境中污染物聚集吸湿增长造成。(5)中低空弱的下沉气流及近地面辐合风场是雾霾天气得以发展维持的动力因子。

A long period of heavy fog and haze event took place in North China Plain from November 23 to December 3 in 2018.Using the conventional meteorological observations,NCEP/NCAR reanalysis data and contaminant concentration data,this paper,taking Puyang of Henan Province as an example,analyzes the large-scale circulation background,characteristics of weather conditions and dynamics in boundary layer and pollution status in order to reveal the causes and maintenance mechanism of this pollution process in three stages.The results show that:(1)This fog-haze pollution occurred in the background of high-level zonal circulation,North China was under the control of the northwest airflow in front of the high ridge,frequently affected by the downsliding short wave trough.(2)The activity of cold air was weak.The middle and lower layers was controlled by warm ridge,which caused strong inversion in the boundary layer and restricted the vertical diffusion of water vapor and pollutants in the lower layers.(3)The ground surface was controlled by equipotential field or weak cold high pressure behind the front,not conducive to the horizontal diffusion of pollutants.(4)When thick fog was formed in the early stage,the strong inversion layer was close to the ground below 900 hPa,with low visibility and serious pollution.When haze was severe in middle stage,the stronger inversion layer moved up to 900—850 hPa,and double-layer inversion appeared.Although visibility was good at that time,pollution was still very serious.The heavy fog and haze in the later stage were mainly caused by the accumulation and hygroscopic growth of pollutants in high humidity environment.(5)The weak downdraft and convergence wind field near the ground are the dynamic factors for the development and maintenance of this fog and haze weather.