Abstract: Based on the Tropical Storm and Hurricane WX products ( WX-TROPL) , 596 tropical disturbances generated over the Northwestern Pacific during 2000-2008 are analyzed, 456 of which occur in summer half year (May to October). The frequency peaks in August ( 11. 6 per year in average) . There are 369 disturbances generated in the monsoon trough. The average development rate of disturbances is 43. 8% , while the peak value 54. 8% appears in August, and the neap value 20% appears in February. The ENSO3. 4 index at the end of year has a high negative correlation with the frequency of disturbances in the next summer half year, and the coefficient reaches 76. 1% . The stronger peak value of La Nina's signal appears, and the longer it lasts, the higher frequency of disturbances in the next summer half year turns up. Over the Northwestern Pacific, most disturbances generate in the South of 15°N in winter half year, and scatter between 0°-35°N in summer half year. Using data derived from satellites, it is implied that the tropical disturbances over the Northwestern Pacific all generate in the high value areas of lower level vorticity and latent heat release.

Key words: tropical disturbances, frequency, monsoon trough, vorticity at lower level, the latent heat release

摘要： 利用热带气旋预警资料( WX-TROPL) , 统计了2000?2008 年西北太平洋热带扰动的频数和时空分布, 发现2000?2008 年西北太平洋共生成热带扰动 596 个, 有456 个集中在夏半年( 5?10 月) , 并在 8 月份达到峰值( 年均11. 6 个) 。全年热带扰动生成于季风槽内的有 369 个。热带扰动的平均发展率为 43. 8% , 其中在 8 月最高, 达54.8% ; 2 月最低, 仅为20% 。年末 ENSO3. 4 指数与下一年夏半年的扰动频数负相关可达 76. 1% , 拉尼娜效应信号的峰值越强(弱)和持续时间越长(短)的年份, 下一年夏半年西北太平洋热带扰动生成频数越多(少)。就整个西北太平洋而言, 冬半年扰动主要集中在 15°N 以南, 夏半年则分散在 0°?35°N 的广大区域内。进一步利用卫星资料对冬夏半年的低层相对涡度和水汽潜热释放等条件的分析表明西北太平洋热带扰动生成在低层涡度和潜热释放的高值区。

关键词: 热带扰动, 频数, 季风槽, 低层涡度, 潜热释放