中山市一次大雾天气过程的成因诊断

利用Micaps资料、NCEP再分析资料和中山市紫马岭观测站的逐时整点能见度、气温、相对湿度、风等资料，对2012年2月29日—3月3日发生在中山市的一次平流雾天气过程进行分析，结果为：（1）该次大雾过程是在下垫面温度较低、温度露点差在1℃以下，相对湿度在90％～95％，风速较小等气象条件下形成的；（2）近地面层弱辐合、中低层弱辐散的散度场配置，低层暖湿平流的增湿作用，以及逆温层的存在均为大雾的形成和维持提供了有利条件；（3）冷空气势力减弱，地面开始增温导致逆温层破坏、水汽不饱和使能见度迅速回升，大雾天气结束。

Analysis of a heavy fog event in Zhongshan

Based on the MICAPS,NCEP reanalysis data and the observational data from a Zhongshan observation station, this paper studies a heavy advection fog event dated from February 29 to March 3, 2012, and the results are showed as follows：（ 1 ） Low temperature on the underlying surface, smaller -than -1℃ temperature/dew point contrast,large relative humidity and small wind speed are the main factors of formation of the heavy fog event; （2） The allocation of weak convergence at the near - surface level versus weak divergence at the mid - and lower - level, the moistening effect of a low - level warm and humid ad- vection and the presence of temperature inversion are all favorable for the formation and maintenance of the heavy fog;（3 ）When the cold air becomes weaker, the inversion layer is destroyed because of the rising of the surface temperature, and the water vapor in the air turns to be unsaturated, the heavy fog comes to an end.