热带大气季节内振荡对西北太平洋地区热带气旋路径的影响

IMPACT OF INTRASEASONAL OSCILLATIONS OF TROPICAL ATMOSPHERE ON TC TRACK CHANGE OVER THE WESTERN NORTH PACIFIC

利用NOAA的逐日OLR场资料、ECMWF逐日风场(850 hPa)资料、以及美国联合台风预报中心(JTWC)的热带气旋(TC)数据,参考Wheeler和Hendon提出的MJO指数,通过Combined-EOF方法定义热带20～90 d振荡(ISO)的指数,对西北太平洋(WNP)区域进行ISO不同相位的划分,深入研究西北太平洋地区ISO对于热带气旋(TC)路径变化的影响。研究结果表明,在ISO东风位相中,在ISO反气旋性环流东北侧气流影响下,西太副高南侧偏东气流较弱,生成在副高中的TC在140°E以东转折的比率较大;而在西风位相,副高南侧偏东气流受ISO气旋性环流影响加强,生成在该区域的TC在偏东气流引导下首先向西,当西北移动至近海区域后,在西南季风气流以及副高西侧偏东南气流的共同作用下,容易发生顺时针的北折,因而在140°E以西转折类的TC比率较高。还分析了台风个例中的ISO流场形势,发现当ISO气旋(反气旋)性环流中心与热带气旋中心重合时,热带气旋路径会发生突然的右折。

By using Outgoing Longwave Radiation （OLR） data from NOAA, daily wind （850hPa） data from ECMWF and tropical cyclones （TC） data from Joint Typhoon Warning Center （JTWC）, the impact of Intraseasonal Oscillation （ISO） on tropical cyclone activity over the Western North Pacific （WNP） is studied in this paper. The index of 20- to 90-day oscillation is defined by referring to the MJO index defined by Wheeler and Hendon. During the easterly phase of ISO, the southeast flow of the west Pacific subtropic high is weakened by the anticyclonic circulation of ISO, and TCs prefer to change their tracks to the east of 140°E. During the westerly phase, with the southeast flow of the west Pacific subtropic high strengthened by the cyclonic circulation of ISO, the westward （northwestward） movement of TCs tend to change their tracks to the west of 140 °E. Case studies of some tropical cyclones are discussed in this paper. The result shows that TCs may exhibit sudden poleward track change while their centers coincide with the center of the cyclonic circulation （anticyclonic circulation） of ISO.