近年广西典型“回南天”现象成因分析

Causal Analysis of Typical''High-Humidity Weather"Events in Guangxi in Recent Years

利用NCEP/NCAR的2.5°×2.5°格点再分析资料以及南宁站气温、露点、能见度、气压等常规观测资料与河池、北海站探空资料,采用统计分析和典型个例分析相结合的方法,分析了2005—2013年广西＂回南天＂过程的天气形势和气象要素特征。结果发现：1不同影响程度＂回南天＂发生前均受到较长时间的冷空气影响;2＂回南天＂发生时,地面有暖低压或倒槽发展,中高纬度没有明显的冷空气南下,850hPa和925hPa上南风强盛,锋区逆温接近近地层,温度骤升,气压剧降,湿度加大,当日14：00露点温度高于当日最低气温;3＂回南天＂结束方式有两种：冷性结束和暖性结束;4＂回南天＂预报依据：如果广西冬春季在较长时间的冷空气影响之后,925hPa温度和湿度突增,同时预测到未来1~2天,14：00露点温度将高于当天最低温度。

Combining statistic analysis with typical case analysis method,by use of the NCEP/NCAR grid reanalysis data（2.5°×2.5°）,and routine observation data such as temperature,dew-point temperature,visibility,pressure in Nanning,and radiosonde data in Hechi and Beihai,the circulation pattern and meteorological element features of several typical＇＇High-Humidity weather＂in Guangxi from 2005 to 2013are analyzed.The results show that：（1）＇＇High-Humidity weather＂ events of different degree are influenced by the stronger cold air before it;（2）＇＇High-Humidity weather＂occurs when the dew-point temperature at 14：00is higher than the lowest temperature of that day and the temperature,and humidity increase suddenly,with the development of warm low or inverted trough and no obvious southward cold air in mid-high latitude,as well as the strong south wind prevails at 850 hPa and 925 hPa,and the front inversion layer is on the ground;（3）＇＇High-Humidity weather＂usually disappears in two ways：cold ending and warm ending;（4）if Guangxi is affected by longer cold air in the winter and spring,and the temperature and humidity suddenly increases at 850 hPa and 925 hPa,and the dew-point temperature at14：00is higher than the lowest temperature of that day in the further one or two days,＇＇High-Humidity weather＂can be forecasted.