荆门市大雾特征分析及预报方法研究

Study on Characteristics and Forecasting Methods of Heavy Fog in Jingmen City

使用荆门站2006-2015年的大雾观测资料,从年际到月际、日际分别给出了该站点大雾发生的频次分布规律,并统计出大雾发生时及之前各气象要素场的特征,结合天气形势建立大雾的综合预报指标。结果发现,荆门市大雾主要为辐射雾,发生次数冬季最多,春季次之,秋季居中,夏季最少;08时(北京时,下同)之后持续出现1~3h的情况居多,超过5h的较少。前一日14时相对湿度≥50%,湿度越大,当日出雾可能性越大;若相对湿度≤40%,可以不考虑雾的发生。前一日02、08、14、20时与预报日当日02时这5个时次的风速均≤3m/s,当日出雾可能性较大。前几日内有降水发生,可增大预报日当日出雾概率;前一日20时天空无低云,对次日出雾有利。荆门市大雾发生时的天气形势可分为3种类型,即持续偏西气流型、弱脊过境型、槽后西北气流型;其中以槽后西北气流型出现最多,前两种类型发生的频率大致相等。

This study analyzed the temporal characteristics of heavy fog and its relations with meteorological elements in Jingmen Station from 2006 to 2015.The results showed that radiation fog was the main type of fogs in the Jinmen Area,which occurred mainly in winter,followed by spring,autumn,and summer in a descending order.The dense fogs generally appeared in the early morning,which lasted from one to three hours.The occurrence of fogs was related to relative humidity,wind, low clouds,and precipitation.The occurrence of fog may not be considered if the relative humidity at 14 BT of the previous day was≤40%.However,the possibility of fogging was greater if the relative humidity was≥50%.If the wind speed was≤3 m/s at 02, 08,14,20 BT of the previous day and 02 BT on the forecast day,the possibility of fogging was large.Precipitation that occurred within a few days before could increase the probability of fogging.At 20 BT on the previous day,there was no low cloud in the sky,which promoted the formation of the sunrise fog.Three types of heavy fogs in the Jinmen Area can be classified:continuous westward airflow type,weak ridge transit type,and the northwest airflow type,with the later one occurring at the highest frequency and the former two occurring at a similar frequency.