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《Meteorological Science and Technology》 2017-04
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Meteorological Causes of a Regional Persistent Fog and Haze Event in Liaoning

Hou Yahong;Xu Fangshu;Zhang Rui;Zhao Miao;Ming Huiqing;Liaoning Meteorological Service Center;Meteorological Service in Dongling District of Shenyang;  
Foggy and hazy weather occurred frequently and worsened air quality dramatically during recent years.Investigating the causes and improving the prediction for fog and haze are essential to guide the public and protect public health.This paper utilizes the observational data from 62 national-level automatic weather stations in Liaoning and the reanalysis data from NCEP to analyze the general-circulation background,forming conditions and persistency causes for the fog and haze process occurred from 7 to 14 November 2015 in Liaoning.Results indicate:(1)The general circulation,including an upper-level westsouthwest flow,a low-level warm ridge,a reversed surface trough,and a weakened surface pressure,provided favorable synoptic conditions for the fog and haze event.(2)Temperature inversion was the critical cause for this persistent fog and haze event.The inversion had different structures for foggy and hazy stages,with a lower top and thinner layer for intense fog but a higher top,a thicker layer and even multiple simultaneous inversion layers for haze.(3)Water vapor content was the key factor for the conversion between fog and haze.A 95% relative humidity near the surface favors fog genesis,while a 60% to 70% is optimal for haze.The specific humidity increased when fog turns into haze,whilst it decreased with a reversed conversion.(4)The weak rising motion near the surface and the weak sinking at middle-upper layers dynamically intensified this fog-haze event.(5)The characteristics of meteorological elements differ substantially before and after the fog and haze,which provides references for predicting fog and haze.
【Key Words】: fog and haze general-circulation background temperature inversion stable stratification humidity dynamical condition
【Fund】: 辽宁省科技厅基金项目(辽宁省大气灰霾的污染形成机制及预报预警技术研究2013229031)资助
【CateGory Index】: X513
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