近40年西江流域前汛期致洪暴雨期间降水的低频振荡特征分析

ANALYSES OF INTRASEASONAL OSCILLATION CHARACTERISTICS OF FLOOD-CAUSING RAINSTORMS IN XIJIANG RIVER VALLEY DURING ANNUALLY FIRST RAINING SEASON IN THE PAST YEARS

利用西江流域9个代表站的降水资料和NCEP/NCAR再分析资料,运用小波分析和带通滤波等方法,对1968、1994、1998、2002和2005年西江流域汛期致洪暴雨过程低频特征进行了分析。这5年西江流域前汛期致洪暴雨期间存在较明显的准双周振荡,西江流域前汛期致洪暴雨是南北冷暖低频系统交汇后发展的结果,来自低纬海洋的低频暖湿气流和来自高纬的低频干冷气流在西江流域附近相遇是造成西江流域前汛期致洪暴雨的主要原因之一,西江流域前汛期致洪暴雨发生期间都有低频正涡旋系统控制或传入,有利于低层水汽的辐合,这对致洪暴雨过程的发生起着重要作用。

Based on the dally precipitation data of nine stations representing the Xijiang River valley and the NCEP/NCAR reanalysis data, the wavelet analysis and band-pass filter methods were used to investigate the atmospheric intraseasonal oscillation characteristics of flood-causing rainstorms in the valley during the annually fh-st raining seasons in 1968, 1994, 1998, 2002 and 2005. The results show that the daily precipitation there exhibits significant quasi-two-week （10~20 d） oscillations. The flood-causing rainstorms in the valley were mainly associated with the confluence of low-frequency warm and humid airflow in the lower latitudes and cold and dry airflow in the higher latitudes. The low-frequency vortexes were propagating or in control when this type of rainstorms took place over the Xijiang River valley, being favorable for the convergence of moisture at lower levels and thus vital for the formation of the rainstorms.