中文摘要：

利用近58年（1950～2007年）热带气旋资料,研究了南海（5°N～25°N,110°E～120°E）和西北太平洋（5°N～25°N,120°E～180°）两个区域热带气旋生成频数的年际变化和季节变化特征,结果表明西北太平洋热带气旋生成频数明显多于南海,且两区域的热带气旋活动表现出明显的区域性差异。在年际变化上,两者之间相关系数仅为-0.09,即南海和西北太平洋热带气旋生成频数在变化上相对独立。在季节变化上,西北太平洋热带气旋生成频数主要决定了整个西北太平洋明显的季节变化特征,而南海热带气旋生成频数在活跃期5～11月内季节差异不够明显,8～9月为相对盛期;特别地,从热带气旋频数相对于整个西北太平洋所占比率来看,5～6月南海区域由前期的寂静期骤然上升至31.7%～33.8%,使得5～6月成为全年比率中最突出的2个月份。对上述热带气旋活动区域性差异的可能原因进行了分析,初步显示在年际变化上ENSO对南海热带气旋生成频数的影响是显著的;在季节变化上,5～6月南海出现了较之西北太平洋更加有利于热带气旋生成的动力条件（季风槽）和热力条件（高海温）,这可能是南海热带气旋生成频数相对于整个西北太平洋所占比率在5～6月成为全年最突出的两个月份的主要原因。

英文摘要：

The interannual and seasonal variation features of the tropical cyclone（TC） frequency are analyzed over the South China Sea （SCS）（ 5°N-25° N,110°-120°E） and the western North Pacific （WNP）（ 5°N-25°N,120°E-180°） ,using the 58-year （1950-2007） TC dataset from the China Meteorological Administration. The results indicate that the TC frequency over the WNP is higher than that over the SCS,and the TC activities over the two regions show significant regional differences. For the interannual variation,the correlation coefficient is -0.09 between the two regions,which means that the TC frequencies over the SCS and the WNP change almost independently. For seasonal variation,the TC frequency over the WNP shows a clear seasonal variation similar to the well known seasonal variation in the whole WNP（the WNP and the SCS）,while in the SCS,the active period of tropical cyclone activity is from May to November,with small intra-seasonal variation showing peak phase from August to September. In particular,from the view of the rate of tropical cyclone frequency to that in the whole WNP,the rate rises sharply to 31.7%-33.8% during May-June from the inactive period from January to April in the SCS,making May-June being the most prominent period with the biggest rate. Further study shows that ENSO influences TC frequency over the SCS significantly in inter-annual variation,and its role doesn＇t play through the underlying surface ocean but maybe through other means such as the atmospheric circulation. For the seasonal variation,during May-June,the dynamic conditions （monsoon trough） and thermal conditions （high sea surface temperature） in the SCS are more favorable for TC genesis than those in the WNP,this may be the possible reasons for the rate of TC frequency in the SCS to that of the whole WNP becoming the biggest from May to June.