北京城市浓雾特征及其与交通预报服务的关系

The urban thick fog features and its relationships to traffic weather services in Beijing

使用2007—2010年北京地区18个道面自动气象站能见度在1000 m以下时的气象资料及同期北京管界内高速公路交通资料,对北京城市浓雾特征及其与交通预报服务的关系进行了探讨。结果表明:1)北京管界内高速公路封闭90%以上因浓雾引起。2)浓雾具有明显的日变化和年变化,高发、低发时段分别在05—09时和12—18时,浓雾主要集中在9—12月,6、7月最少。3)空间分布上,浓雾频次东南高,城区低,80%以上的浓雾出现在大兴和通州两区。4)浓雾变化具有突发性和"象鼻形"先期振荡特征。5)浓雾期间能见度变化与气象要素关系密切,近地面偏南风和偏东风最有利浓雾生成发展,西北风最有利浓雾消散;风速减小,气温下降,湿度增大,能见度降低,有利浓雾生成和发展;风速增大,气温升高,湿度减小,能见度上升,有利浓雾减弱消散;湿度减小滞后于能见度上升;浓雾维持阶段,各要素变化很小。

Based on the observation data of the visibility below 1000 m from 18 automatic weather stations on expressway surface and traffic data in Beijing area from 2007 to 2010, the urban thick fog features and its relationships to traffic weather services in Beijing was investigated. The main conclusions are as follows： （1） more than 90% of expressway closed cases in Beijing owes to the thick fog. （2） Tile thick fog whose visibility is below 200 m happens mostly between 05 a.m. and 09 a.m. and the less between 12 a.m. and 18 p.m. in a day, while in a year, it happens mostly from September to December and less in June and July. （3） About 80% of the thick fog cases with visibility below 200 m hap- pen in the Daxing and Tongzhou districts in the southeast parts of Beijing, while the few cases happen in urban area.（4） The thick fog has fea- tures like suddenness and ＂trunk-like＂ fluctuation before the formation of thick fog. （5） During the period of thick fog the visibility changes with the meteorological elements such as wind, temperature and relative humidity. The southerly wind and easterly wind near the ground are advantageous to the formation and development of thick fogs, while the northwest wind is advantageous to the dissipation of thick fogs. It is beneficial to the formation and development of thick fog that the wind speed becomes low, the relative humidity is increased, temperature drops down, and the visibility is reduced. The wind speed, relative humidity, temperature, and the visibility are all changed a little bit as thick fog maintains. During the period of thick fog dissipation, the wind speed becomes high, the relative humidity is reduced, temperature rises, and the visibility becomes better. But the reduction of relative humidity is later than the rise of the visibility.