Based on the conventional observation data, an objective analysis is made for causes of the continuous heavy fog occurred on November 26 to 28, 2011, at Taoxian airport. Results show that the heavy fog weather has the characteristics of mixed nature, with alternate occurrence of frontal fog, radiation fog and convection fog. Among all the causes, the ‘pocket’-shape terrain of the airport with surface wind in winter is conductive to the formation and maintenance of the fog. And weak positive divergence zone between 850 to 700hpa promotes the maintenance of inversion layer between upward motion and downward motion. The subsequent 925hpa low turbulence plays a key role on the fog dissipation.%利用常规观测资料，对2011年11月26-28日沈阳桃仙机场出现持续大雾天气进行客观分析与应急服务总结。结果表明：此次大雾的天气过程具有混合型的特点，雾的性质随着时空变化而转变，由锋面雾、辐射雾和平流雾交替转换。其中，冬季桃仙机场“口袋型”地势与地面风配合有利于大雾的形成与维持；850-700 hPa之间弱的正散度区，促进了上升运动区与下沉运动区的界面中的逆温层的维持；后续925 hPa低空湍流的发展对大雾消散起到了关键作用。
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