超强台风“威马逊”近海加强与低频水汽输送的关系及前期信号

利用NCEP/NCAR再分析资料以及中国气象局上海台风研究所（简称上海台风所）整编的《热带气旋年鉴》，分析了超强台风“威马逊”在南海加强过程中水汽输送的变化特征，着重探讨台风强度变化与10~30 d低频水汽输送的关系，并从低频场出发寻找台风强度变化的前期信号。研究结果表明:（1）“威马逊”有两条主要的水汽通道，分别为孟加拉湾通道和南海通道，孟加拉湾通道的水汽输送强度大于南海通道；（2）“威马逊”近海加强与10~30 d低频水汽输送有紧密的联系。在热带低频系统作用下，孟加拉湾通道的低频偏西水汽和南海通道的低频偏南水汽在南海汇聚，为“威马逊”的增强提供了有利条件；（3）对于在海南岛东部登陆的台风，其登陆强度与超前5~7 d孟加拉湾通道的低频偏西水汽输送呈现显著的负相关，与南海通道的低频偏南水汽输送有较弱的负相关。若前期从两个通道截面流入的低频水汽输送通量位于低频振荡的谷值时，则有利于其后5~7 d台风在南海加强，反之减弱。 

The Relationship Between the Offshore Intensification of Super Typhoon Rammasun and Low-Frequency Vapor Transportation and Its Precedent Signal

Using NCEP/NCAR reanalysis data and tropical cyclone yearbooks compiled by Shanghai Typhoon Institute of CMA, we analyzed the variation characteristics of vapor transportation when the super typhoon Rammasun intensified in the South China Sea (SCS), mainly discussed the effect of 10~30 d low-frequency vapor transportation on Rammasun intensification, and identified the precedent low-frequency signal of typhoon variation from low-frequency circulation field:(1) Rammasun has two main vapor transportation channels, one in the Bay of Bengal (BOB) and the other in the SCS, and the intensity of the BOB channel is greater than that of the SCS channel; (2) The offshore intensification of Rammasun has close relationship with 10~30 d low-frequency vapor transportation. Under the effect of tropical low-frequency system, low-frequency west vapor transported from the BOB channel and southward transported vapor from the SCS channel converge over the SCS, providing favorable conditions for the intensification of Rammasun; (3) For the typhoons landing on the east of Hainan Island, their landing intensity has significantly negative correlation with low-frequency vapor transportation from the BOB channel, and relatively weak negative correlation with the vapor transportation from the SCS channel 5~7 d in advance. If the low-frequency vapor transportation flux inflowing from the cross sections of the two channel is at the low-value phase of the low-frequency oscillation, it is good for the typhoon to intensify over the SCS 5~7 d later, otherwise weakening.