中文摘要：

根据中国气象局上海台风研究所整编的热带气旋最佳路径数据集（CMA-STI）,以及定义的热带气旋（Tropical Cyclone,TC）群发标准,分析了南海—西太平洋地区的低频振荡特征,及其对TC群发活动的影响,研究了TC群发与季风槽的关系。结果表明,孟加拉湾—西太平洋的近赤道地区有两支主要的对流区,分别位于南海—西太平洋地区和孟加拉湾东南部。10~20 d大气准双周振荡（Quasi-Biweekly Oscillation,QBWO）周期是南海—西太平洋地区对流活动的主要周期,大部分年份QBWO占原始序列的方差贡献达20%以上。QBWO的强度具有明显的年际变化,20世纪80年代以前强度变化较大,80年代之后变化较小。根据定义的TC群发标准,发现1990年6—9月西北太平洋地区共有4次TC群发过程,都发生在低频对流活动的湿位相。分析对流活动干位相—湿位相—干位相的演变,发现TC的群发期集中在湿位相,湿位相期间大气低层为低频气旋性环流,较强的正涡度有利于初始涡旋扰动的形成和发展,为TC群发提供了有利的环流背景场。根据定义的季风槽强度指数,发现季风槽强度与TC群发过程有很好的对应关系,由于季风槽的活跃使得对流活动处于湿位相期,同时季风槽区提供了有利的正涡度条件,促使TC群发活动产生。

英文摘要：

Based on the tropical cyclone（ TC） datasets provided by the Shanghai Typhoon Institute of China Meteorological Administration,the characteristics of the low-frequency oscillation over the South China Sea—western North Pacific（ SCS—WNP） and its modulation of the clustering characteristics of TCs are studied.The results showthat there are two convection regions located in the SCS—WNP and southeast Bay of Bengal. The wavelet analysis and power spectrum analysis results showthat the SCS —WNP convective activities exhibit an intraseasonal oscillation with a period of 10—20 days. In most years,the variance contribution of the quasi-biweekly oscillation（ QBWO） accounts for more than 20% of the original sequence,showing that the QBWO in the SCS—WNP plays an important role in atmospheric low-frequency oscillation. The strength of the QBWO has obvious interannual variability,with the strength of change greater before the 1980 s and smaller after the 1980 s.There were two significant oscillation periods in the SCS—WNP from June to September in 1990： 15—30days and 8—14 days. TCs were prone to occur in the wet phase,and when the wet phases of the two convections overlapped,the frequency of TCs was highest. According to predefined standards of TCs clustering,there were four TC clusters from June to September in 1990,and they showed a close relationship with the evolution of the low-frequency circulation. There was a complete wet phase from 24 July to 2 August,during which time the development of TCs was strong. The period 4—9 August was a complete dry phase,and in this time TCs gradually weakened and disappeared. The results showthat TCs are prone to occur and develop in the wet phase. During the wet phase,there is low-frequency cyclonic circulation in the low-level atmosphere,and the strong positive vorticity is conducive to the formation and development of the initial vortex disturbance,which is favorable for TCs clustering. With the westward propagation of the low-frequency oscillation,the