Taking two tropical cyclones that landed southern China and caused great damage in summer of 2001 and 2006 as examples,using the dataset of CMA-STI Tropical Cyclone Optimal Tracks,the NCEP/NCAR reanalysis data and the intensive surface observations,this paper compares the large scale circulation features of maintenance over land and enhanced rainstorm from Durian（0103） in 2001 and Bilis（0604） in 2006.The conclusions are as follows：（1）After landing,Durian interacts with the mid-latitude westerly trough,forming a pattern of ＂North trough and South vortex＂.After landing,Bilis is blocked by the western Pacific subtropical high（WPSH）,the northern high-pressure dam,and the extending southwest high pressure ridge of WPSH in the south side,allowing its cyclonic circulation to be maintained.（2）During the period of Durian and Bilis over land,the cross-equatorial flow increases significantly.The cross-equatorial flow nearby 100°E is remarkable in 2001,but the cross-equatorial flow nearby 80°E has outstanding performance in 2006.The cross-equatorial flows strengthen the southwest monsoon,which keep providing plentiful water vapor for the declining Durian and Bilis,leading to their long time maintenance over land instead of quick decaying.（3）East Asian monsoon manifest significant low-frequency oscillation,with main periods of 10—20 d in 2001 and 30—60 d in 2006.Low-latitude monsoon surge,characterized by different atmospheric low-frequency oscillations,experience remarkably northward propagation.In an extremely active stage of the low-frequency oscillation of low latitude summer monsoon,the monsoon surge is the strongest and intrudes into the circulations of Durian or Bilis,corresponding to the enhanced rainstorm.In addition,the convergence of low-frequency airflows and transport of low-frequency water vapor aslo play important roles in the enhanced rainstorm from Durian and Bilis.%以2001和2006年盛夏登陆中国南方并造成巨大灾害的两次热带气旋过程为例,利用＂CMA-STI热带气旋最佳路径数据集＂、NCEP/NCAR再分析资料及地面加密观测资料,对2001年0103号＂榴莲＂和2006年0604号＂碧利斯＂热带气旋陆上维持和暴雨增幅的大尺度环境场及成因进行了对比分析。结果表明：1）＂榴莲＂登陆后与中纬度西风槽发生相互作用,构成了典型的＂北槽南涡＂天气形势,＂碧利斯＂登陆后受西太平洋副高、北方大陆高压坝和南侧副高向西南方向延伸的高压脊所包围,有利于其环流维持。2）＂榴莲＂和＂碧利斯＂陆上维持期间越赤道气流明显增强,但是在＂榴莲＂活动期间,100°E附近越赤道气流表现突出,而在＂碧利斯＂陆上活动期间,80°E附近越赤道气流尤为显著,它们都增强了当时的西南季风,把大量来自热带海洋的水汽注入登陆后减弱的＂榴莲＂和＂碧利斯＂环流,使其非但没有很快减弱消亡,反而能在登陆后长时间维持不消。3）2001和2006年东亚夏季风存在明显低频振荡,2001年低纬夏季风10～20d低频振荡显著,而2006年则以30～60d低频振荡为主,由不同低频振荡周期表示的低纬季风涌均存在明显的北传特征。当低频振荡处于极端活跃位相时,季风涌最为强盛并侵入＂榴莲＂和＂碧利斯＂环流系统,正好对应着当时的台风暴雨剧烈增幅。此外,低频气流的辐合和低频水汽输送也是＂榴莲＂和＂碧利斯＂暴雨增幅的重要原因。
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