摘要
利用中国气象局上海台风研究所整编的热带气旋最佳路径资料、向外射出长波辐射(OLR)和NCEP/NCAR再分析风场资料,研究了1991年夏季西北太平洋热带气旋的群发性特征及其与大气季节内振荡的关系。结果表明,1991年6~9月西北太平洋地区的对流活动存在20~60天的准周期振荡,该区域的热带气旋活动也具有这种频率的季节内变化,即热带气旋的活动具有明显的群发性和周期性。进一步分析表明,热带气旋易集中出现在大气季节内振荡的湿位相,这是因为湿位相期间大气低层维持的较大尺度的低频气旋性环流为天气尺度的热带气旋的生成提供了有利的背景环流场。低频气旋中心东南侧的不稳定低空西风急流容易激发出一些小扰动,低空的低频正涡度异常又有利于这些初始小扰动的增长,同时,热带气旋发生势(genesis potential)表现为正距平,说明热带气旋发生发展的垂直风切变条件容易满足,因而导致热带气旋的相继群发。
The NCEP/NCAR reanalysis, outgoing longwave radiation (OLR) and tropical cyclone datasets are employed to investigate the clustering characteristics of tropical cyclone activities over the western North Pacific from June to September in 1991 and their associations with intraseasonal oscillations (ISOs), in which tropical cyclone data refer to the best tracks from the Shanghai Typhoon Institute of China Meteorological Administration. Tropical convective activities are found to exhibit an intraseasonal oscillation with a period of 20 - 60 days during the summerof 1991 over the western North Pacific. Within this region, tropical cyclone occurrences are modulated by a similar period, i.e., tropical cyclone activities show features of periodicity and clustering over there. The tropical cyclones are prone to occurring frequently in the form of a cluster during the wet phase of the ISO, because anomalous cyclonic circulation at the lower levels forms a favorable background circulation for the generation and development of tropical cyclones. The unstable westerly jet on the southeastern side of such an anomalous cyclone in the lower troposphere induces frequently some disturbances, and the amplitudes of these initial disturbances increase due to positive vorticity anomalies. Meanwhile, positive genesis potential anomalies of tropical cyclones during the wet phase of the ISO indicate that the favorable vertical shear conditions are satisfied for the development of tropical cyclones, leading to the clustering of tropical cyclone.
出处
《大气科学》
CSCD
北大核心
2009年第5期950-958,共9页
Chinese Journal of Atmospheric Sciences
基金
国家重点基础研究发展规划项目2006CB403603
国家自然科学基金资助项目40821092
中国科学院大气物理研究所LASG开放课题
浙江省科技厅项目2007C13G1610002
关键词
季节内振荡
热带气旋
群发性
intraseasonal oscillation
tropical cyclone
clustering