藏北一次局地爆发性浓雾特征与成因分析

利用那曲市色尼区常规气象观测资料，结合NCEP（1°×1°）、Era5（0.25°×0.25°）再分析资料，从天气学角度对2019年4月10日藏北一次浓雾天气的形成机制、物理结构特征以及局地性爆发的成因进行诊断分析。结果表明：此次浓雾具有局地爆发性特征；前期积雪融化的水汽蒸发配合风场辐合作用，为此次大雾的形成提供了水汽条件；500 hPa环流背景及边界层内上层暖平流与下层冷平流配置，为大雾的形成提供了弱风与稳定层结条件，从而雾得以发展且维持；夜间少云，地表净辐射加强，降温冷却作用导致水汽达到饱和状态，利于水汽凝结形成无数悬浮于空气里的小雾滴；近地层风速小、逆温及下沉运动使水汽不易向高空扩散，在相对有限的空间内水汽大量汇聚，导致大雾爆发性发展；大雾的局地性与特殊地形关系密切。

Characteristics and cause analysis of a local explosive fog in north Tibet

Based on the conventional meteorological observation data in Seni district of Nagqu, combined with the NCEP (National Center for Environmental Prediction, 1°×1°) and Era5 (0.25°×0.25°) reanalysis data, the formation mechanism, physical structure characteristics, and the cause of local occurrence of thick fog in north Tibet on April 10, 2019, were diagnosed and analyzed from the perspective of synopology. The results show that the fog is characterized by local outbreaks. The evaporation of water vapor from the melting snow in the early stage cooperated with the wind field is helpful to the formation of the fog. The 500 hPa circulation background configured with warm advection on the upper layer and cold advection on the lower layer in the boundary layer are involved in the formation of the fog so that the fog can be developed and maintained. There are fewer clouds at night, and the net radiation on the surface is strengthened. Strong net radiation on the ground, and a cooling effect leading to the saturation of water vapor, which is conducive to condense water vapor and form countless small droplets suspended in the air. The low wind speed, inverse temperature, and sinking motion in near formation make water vapor difficult to diffuse into the upper air, so large number of water vapor converges in a relatively limited space, leading to the explosive development of fog. The locality of fog is closely related to the special terrain.