中文摘要：

利用西北太平洋编号台风资料、NCEP/NCAR再分析资料和NOAA向外长波辐射（outgoing longwave radiation,OLR）资料等,选取西北太平洋热带气旋频数异常偏少的2010年和1998年,诊断分析ENSO事件及其东亚夏季风环流异常与热带气旋频数异常的关系,给出东亚夏季风系统部分成员影响热带气旋频数的天气学图像：由春入夏,赤道东太平洋海温异常偏暖,赤道哈得来环流偏强,沃克环流偏弱;西太平洋副热带高压异常强大,位置偏西;季风槽位置偏南,东西向不发展;南海、西太平洋越赤道气流偏弱;异常热源和水汽汇偏南,南海和菲律宾以东地区对流活动受到抑制,热带对流活跃区位于赤道以南;热带气旋生成个数明显偏少,位置偏西。

英文摘要：

The tropical cyclone frequencies in the northwestern Pacific in 2010 and 1998 are far less than the normal frequency,so the diagnostic analyses are performed on relationships between ENSO events,East Asian summer monsoon circulation anomalies and the tropical cyclone frequency anomalies based on the data of serially numbered typhoons in the northwestern Pacific,the data derived from NCEP / NCAR reanalysis dataset and the interpolated outgoing longwave radiation（ OLR） data provided by NOAA. The synoptic images of the main memberships of East Asian summer monsoon system influencing the tropical cyclone frequency are given： From spring to summer,the sea surface temperature in the equatorial eastern Pacific is warmer,Hadley circulation is stronger,and Walker circulation is weaker; the West Pacific subtropical high is intensified and moves westward; the monsoon trough extends southward without eastward and westward spread; the cross-equatorial flow in South China Sea and the western Pacific is weaker; the abnormal apparent heat source and apparent moist sink extends southward,and the tropical convective activity is not active in South China Sea and the Philippines,but it is active in south of the equator; thereforethe tropical cyclone frequency is significantly less than the normal and the tropical cyclone moves westward.