北京地区一次持续性大雾的宏观物理特征

The Macro-physical Characteristics of a Durative Fog Event in Beijing

通过分析北京地区2004年11月30日和12月2日出现的两场大雾生成的天气背景,大雾生成阶段和消散阶段的温度、湿度、气压和风场特征,探讨北京地区大雾的宏观物理特征。所用数据资料是通过系留气球探测所得,分析了气象要素的廓线和时间剖面图特征,从而得到了北京地区有雾生成时的天气背景特征;辐射雾与平流雾的能见度变化区别,雾生成时、持续阶段及雾消散前温度场、湿度场的变化特征;逆温层在辐射雾和平流雾中的形成原因和作用都不同;比湿值增大是判断有暖湿平流带来水汽的重要指标;气压变化平稳、缓慢,使强对流没有发生,逆温层不能被冲破,雾能长时间维持。

The macro - physical characteristics of fog in Beijing area are discussed in this paper by case studies of fog events on 30th November and 2nd December, 2004. The weather background for fog formation as well as the temperature, humidity, pressure and wind field characteristics during fog formation and dissipation is investigated. The data used in this paper were obtained by sounding the fog using Tethered Balloon. The characteristics of sounding profiles and time - height cross sections of meteorological elements are analyzed to gain the results as followed： weather background characteristics for fog formation in Bei- jing; differences in visibility change between radiation and advection fog; the changing characteristics of temperature and humidi- ty field during the fog formation, duration and dissipation; differences between radiation and advection fog in the impact of inver- sion layer on fog formation; the increaes of specific humidity being an important index for vapor increase brought by warm and moist advection; duration of fog due to smoothly changing pressure with no significant convection to break the inversion.