2009年夏末秋初广西持续干旱成因分析

An Analysis on the Causes of the Drought in Late Summer and Early Autumn of 2009 in Guangxi

利用1951―2009年广西地面气象观测逐日降水资料和NCEP/NCAR再分析资料,采用一元回归和小波分析方法对历年广西夏末秋初降水气候趋势变化和周期性进行统计分析。结果表明:从历史资料看,广西夏末秋初降水呈显著减少趋势,而且具有2 a、8 a和14 a周期变化特征,2009年处于2 a周期信号偏少期。造成广西夏末秋初高温干旱的主要原因为:8月副热带高压脊线偏北,东亚槽脊平缓不利冷空气南下,广西常处于高压脊控制;9月副高南落,广西部分地区受副高控制;广西低空呈反气旋的环流形势,低层辐散高层辐合,气流以下沉运动为主,而且水平风速很小,大气稳定;2009年6月太平洋出现了厄尔尼诺现象,并在8、9月得到了发展。

With the daily precipitation data and the NCEP/NCAR monthly reanalysis data in 1951-2009,the causes of the drought in late summer and early autumn 2009 in Guangxi are researched.The results show that the August and September precipitation in the region exhibits a decreasing tendency on a long-term basis and displays significant characteristics of periodic oscillations of 2,8 and 14 years,and 2009 was at the drought phase.The subtropical anticyclone in the western Pacific shifted northward in August,and shifted southward and controled the most parts of Guangxi in September.The trough in Asia was weak in August and September,which was favorable to the maintanence of ridge.Meanwhile there was anticyclonic circulation at 850 hPa and the most parts of Guangxi were under the control of downward current,and El Ni？o was strengthened.Moreover the Ni？o3,4 SST are negatively correlated with the precipitation in August and September.Those would be the main causes of the drought in late summer and early autumn in 2009 in Guangxi.