2007年12月南京大雾频发的多尺度特征研究

MULTI-SCALE FEATURES OF FOG IN DECEMBER 2007 IN NANJING

2007年12月南京的雾日是近30年来出现最多的月份。以此为研究对象,从气候尺度诊断分析发现:AO(北极涛动)的正异常有利于南京地区大气稳定度增加。从天气尺度分析发现:中国沿海20°N地区提前2天的水汽增加,为南京大雾提供了水汽源,西南气旋为水汽输送提供输送途径。通过对东亚地表温度和大气可降水量做双变量经验正交分解(EOF)发现:第一模态可以反映出初冬到深冬的季节变化,有利于大尺度的地表温度下降,第二模态反映了一次大范围的暖湿气流北上的过程,并伴随副高的增强,使南京地区出现连续多湿天气,造成大雾频发。

Abstract： December 2007 became the month in the past 30 years that recorded the most fog days in Nanjing, It is diagnostically studied on the climate scale with the findings as follows. Positive anomalies of Arctic Oscillation （AO） were favorable to the increase of the atmospheric stability. Two days in advance, water vapor increased over the 20 ＂N area on the coast of China to act as a source of water vapor for the heavy fog. A Southwest-China cyclone transferred the water vapor. Running dual-variable Empirical Orthogonal Function （EOF） for the surface temperature and atmospheric precipitable amount in East Asia shows that the first EOF mode reflects seasonal change from early winter to prime-time winter, which is conducive to reduced surface temperature on the large scale, and the second mode reveals the northward advancement of large-scale warm and humid airflow. With the enhancement of the subtropical high, sustained humid weather occurred in Nanjing to cause frequent appearance of fog.