2007年1月初河北省连续大雾的成因分析

对发生在2007年元旦期间河北省大部地区的连续大雾天气从高低空环流形势、物理量场及气象要素场变化等方面进行了分析。发现这次大雾天气发生在500hPa中纬度平直偏西气流、中低层西北气流或弱高压环流以及地面高压前部弱气压场控制的大气环流形势下。大雾前期出现了明显降雪，雪后融化使近地面层湿度迅速增加；大雾期间，夜间辐射明显，近地层大气有逆温层结建立。水汽聚集在近地层通过地面蒸发和辐射冷却而达到饱和。充足的水汽和近地面明显的水汽饱和是河北大部分地区出现连续大雾的重要原因之一。而且这次大雾天气过程近地面层呈弱稳定状态，中高层为稳定状态。

Cause Analysis of a Consecutive Heavy Fog Process in Hebei Province

The consecutive heavy fog occurred in most areas of Hebei Province from December 31,2006 to January 5,2007,was analyzed based on upper and low level circulation patterns,physical quantities and meteorological element fields,etc.The results show that the heavy fog occurred under the atmospheric circulation pattern controlled by the straight westerly air flow at 500 hPa middle latitudes,northwesterly air flow or weak high pressure circulation at middle and low levels,and weak pressure in front of the surface high.Visible snow occurred before the heavy fog,and snow melting rapidly increased the humidity near the surface.During the fog,significant night radiation caused the temperature inversion near the surface.Water vapor accumulated near the surface and was saturated due to surface evaporation and radiation cooling.Ample water vapor and obvious saturation near the surface were the important causes of the consecutive heavy fog.A weak stability near the surface and stability in middle and upper levels presented during this fog event.