一次持续稳定的平流雾天气

A Constantly Maintained Advection Fog

对１９９７年１２月１７～１９日出现在北京地区的平流雾进行了天气学分析，认为此次平流雾是在较为稳定的华北地形槽弱辐合的大尺度条件下，罕见的逆温顶盖（γ＝５．８４℃／１００ｍ）牢牢地置饱和湿空气于２３９．４ｍ以下北京这种特殊的地形中；地面中尺度辐合线和时空剖面图上风的脉动所产生的２００ｍ以下的小尺度辐合线引起的辐合抬升，有利于饱和湿空气不断在山前平原和谷地得以补充和聚集。

The reasons of the constant maintenance of the advection fog in Beijing area from December 17 to 19 in 1997,was synopolically analyzed.It is suggested that under the macroscale condition of the weak convergence which is formed by the relatively stable topographic trough in north China,saturated air is firm in a special terrain Beijing gulf which is below 239 4 m,due to the scarce inversion lid( r =5 84℃/100m);and that the surface mesoscale convergence line and the miniscale convergence line below 200m produced by the fluctuation of the wind on the time height section diagram result in the convergence lift.Thus helped the saturated air constantly being supplied and gathering in plains and valleys.