首都机场浓雾中的能见度突发性振荡及其演变规律

Obrupt oscillation of visibility and its evolution during dense fog events at Beijing capital international airport

利用2000-2011 年北京首都机场每分钟的自动观测资料,对影响首都机场的52 次浓雾过程进行分析,发现浓雾的形成、发展和消散过程中能见度演变具有突发性和振荡性的特征.浓雾中的能见度振荡可分为前导振荡、中间振荡和后位振荡,三者所占比例分别为86.5%、62.5%和79.2%.冷季浓雾比暖季浓雾具有更明显的温度振荡,在影响首都机场的34 次冷季浓雾中,有61.8%的个例具有温度的振荡.辐射雾中温度振荡超前于能见度振荡,而平流雾来临前有温度振荡,雾发生时温度振荡不明显.根据统计结果本文定义了浓雾振荡指数DFOI,并发现DFOI为±0.2 可以作为首都机场浓雾临近预报的阈值,使用该阈值可以将首都机场2000-2011 年的浓雾预警平均提前1～2 h.根据2012 年1 月的实际预警测试,发现单独使用该指数无法区分浓雾、降雪和霾过程,今后在雾的预警过程中还需要引入其他指数.

Theautomaticobservationdatainoneminuteintervalareusedtoanalyze 52 fogeventsthataffectedthetakeoffandlandingofaircrafts at Beijing Capital International Airport(BCIA) from 2000 to 2011. It was found that the visibility evolution of dense fog in the processes of its formation, development and dissipation is abrupt and oscillatory. These oscillations of dense fog can be classified to the leading oscillation, the middle oscillation and the posterior position oscillation. There were 86.5%, 62.5% and 79.2% cases with the leading oscillation, the middle oscillation and the posterior position oscillation. The temperature oscillation in cold season fog is more distinct than that of warm season fog. In the 34 cold season fog events affecting BCIA, there are 61.8% cases including the temperature oscillation. In radiation fog events,the temperature oscillation is slightly ahead of the visibility oscillation. There is a temperature oscillation in a few hours just before the arrival of each advection fog event in cold season, while the temperature oscillation is not distinct at the time of the advection fog occurrence. Based on the statistical results, a quantitative index of the oscillation in dense fog is defined as DFOI(Dense Fog Oscillation Index). It was found that±0.2 can be used as the criterion of nowcasting prediction of dense fog in BCIA, with which an alarm of dense fog can be issued 1-2 hours earlier for the events during 2000 to 2011. According to the result of actual tests in January 2012, it was found that using this index alone could not distinguish fog from snow or haze,other indices must be introduced in the process of early fog warning.