南岭山地高速公路雾区恶劣能见度研究

A Study on Bad Visibility over Foggy Section of Freeway in Nanling Mountainous Region

使用2003年10月—2005年3月南岭山地京珠高速公路粤北段云岩雾区路段5套能见度仪的每分钟能见度资料和3套自动气象站的每分钟温度、湿度、风向、风速等气象要素资料,分析研究了南岭山地高速公路雾区浓雾的能见度特征。结果表明,南岭山地高速公路雾区各月雾日频率以1月最多,近一半的天数都有雾;3月次之,7月最少。11月到次年5月雾日占全年雾日的80%以上,形成明显的“雾季”。南岭山地高速公路雾区浓雾存在日变化,雾的频率在一天内凌晨最高,午后最低,明显比辐射雾的日变化小,说明夜间辐射降温虽然不是南岭山地高速公路雾区起雾的主要原因,但还是起到了一定的加强作用。虽然南岭山地雾区大气中含有丰富的凝结核,南岭山地形成浓雾还是需要较高的相对湿度,相对湿度至少要达到91%以上才能形成雾。在雾区出现5.2 m/s的大风时仍然有雾,有雾时90%以上的风速在3 m/s以下,有几乎一半的浓雾出现时风速在2 m/s左右,这与辐射雾形成时大都是静小风的情况形成了鲜明对照。南岭山地高速公路雾区浓雾受地形影响比较大,迎风坡出现雾的频率比背风坡高。

Using the data from October 2003 to March 2005,such as minutely visibility,temperature,humidity,wind direction and wind speed from five visibility meters and three automatic meteorological stations located at Yunyan foggy section over Nanling mountainous region in north of Guangdong Province of freeway which is from Beijing to Zhuhai,the visibility character of the foggy section is studied.The results show the frequency of fog in January is the highest in whole year,the day numbers over half of January can occur fog,next is March,the lowest is in July.The fog days from the November to May next year occupy over 80% of all year round,forming obvious foggy season.The diurnal variation of heavy fog exist over foggy section of freeway in Nanling mountainous region,the frequency of the fog is the highest in the morning in a day,the lowest in the afternoon,but the range of the diurnal variation is obvious smaller compared to that of radiation fog,revealing temperature drop resulting from radiation cooling is not the main cause for the fog forming over foggy section of freeway in Nanling mountainous region,although the radiation cooling has the enhancing effect on fog forming in some extent.There are plenty of coagulate nuclei in the foggy section,but the forming of heavy fog need condition of relative higher humidity,at least reaching over 91% in Nanling mountainous region.In foggy area when the wind speed is as high as 5.2 m·s^-1,the fog still can occur.Over 90% occurrence of fog is under condition of the wind speed less 3 m·s^-1,and almost half about 2 m·s^-1.It is obvious different from the light wind condition of the forming of radiation fog.The topography has big influence on the forming of the heavy fog,the occurring frequency of fog in the windward side is higher than that in the leeward side.