2004年西北太平洋热带气旋的活动特点与成因研究

STUDY ON THE CHARACTERISTICS OF TROPICAL CYCLONES ACTIVITY OVER THE WESTERN NORTH PACIFIC IN 2004 AND THE CAUSE OF FORMATION

对2004年台风汛期西北太平洋热带气旋的活动特点进行研究总结,进而对其成因做了分析。结果指出：2004年西北太平洋热带气旋主要特点是生成总数较常年略偏多,热带气旋生命史普遍较长、生成时间相对集中、生成源地偏东,转向路径偏多,登陆气旋数多于常年平均值,登陆地段集中且偏北,集中在华东到日本一带。其成因在于：(1)副高面积偏大、强度偏强、位置偏北且西伸脊偏西,同时副高分布形态多呈块状,使得2004年台风的高频活动区向北偏移,直接对华东到日本一带造成威胁,乃至正面登陆影响；(2)澳大利亚高压强大,越赤道气流强,赤道辐合带辐合偏强、位置偏东,造成台风活动比较活跃且源地偏东；(3)西风带环流经向度较常年偏大而且副高多呈块状分布,东西两环副高之间形成的鞍型场有利于台风过此通道北上转向,导致转向台风偏多。

In this paper, we concluded the characteristics of tropical cyclones （TC） activity over the western north Pacific in 2004 and analyzed the cause of formation. Compared with the ordinary year, the annual frequency of TC in 2004 is slightly higher, tropical cyclones in 2004 had a longer life span and occurred in a concentrated period, the source of TC were situated easterly; in all tracks of TC, the recurvature tracks took up larger proportion, the landfall region of TC were located northerly, which concentrated from East China to Japan. The primary causes were as follows. Firstly, the intensity and area of the western north Pacific subtropical high was stronger and greater than usual, its ridge was frequently in the form of cells and stretched north-westerly. Secondly, the convergence of ITCZ was reinforced and the convergence area moved more easterly than usual. Thirdly, the meridionality of the westerlies was bigger than average and the cell-shaped ridge formed a. saddle region.