广西春旱的时空分布特征及成因分析

利用广西具有气候代表性的32个站点1961-2007年逐日降水量资料,引入季节无雨日作为划分干旱的标准,采用EOF分析等方法,分析了广西春旱的时空分布特征;并用NCEP再分析资料、NOAA海温资料、国家气候中心的74项环流特征量资料等,对广西春旱的成因进行了分析。结果表明:从时间变化看,广西春旱的趋势变化不明显,主要以年际、年代际变化为主,从空间分布看,广西春旱以全区一致性型为主要空间分布型;在春旱年,广西上空对流层低层出现偏南-西南气流距平强辐散异常,伴随有明显的水汽通量辐散异常,同时东亚大槽偏弱,阿留申低压明显减弱,中纬度大陆高压减弱,中高纬环流平直,不利于冷空气南下华南;广西春旱年前冬阿留申低压明显增强,大陆高压也增强,冷空气活动频繁,当前冬印缅槽偏弱时,广西春季发生干旱的可能性较大。

Temporal and Spatial Distribution and Causes of Spring Drought Events in Guangxi

Based on the daily precipitation data from 1961 to 2007 in Guangxi and the seasonal non-rainy days as an index for spring drought events,the spatial and temporal characteristics of droughts in Guangxi are analyzed by the EOF method.The mechanisms of spring droughts in Guangxi are further discussed based on the NCEP reanalysis data,NOAA sea surface temperature data,the National Climate Center of the 74 circulation indices.The results show that,in the terms of time changes,the trend change of drought events in spring of Guangxi is not significant,but mainly on inter-annual and inter-decadal time scales.The dominant anomalous patterns of spring droughts show an in-phase distribution of anomalies in the whole area of Guangxi.In the spring drought cases,there exists divergent southwesterly anomalies in the lower troposphere over Guangxi,accompanied by divergent moisture flux over there,while the East Asian trough is weakened,the Aleutian low pressure significantly increase,and the high pressure over mid-latitudes of Euro-Asian continent becomes weakened which leads to a more flat zonal flow in mid-and high latitudes and is not favorable to intensive cold air southward to South China.In pre-winter of spring droughts in Guangxi,Aleutian low pressure is markedly deepened while continental high pressure leads to cold air activities in East Asia.The weaker trough in southern Tibetan Plateau in winter means a possible drought event in the followed spring in Guangxi.