西北太平洋热带气旋快速增强阶段的风速分布特征

WIND SPEED DISTRIBUTION FEATURES OF RAPIDLY INTENSIFYING TROPICAL CYCLONES IN NORTHWEST PACIFIC

利用联合台风预警中心的最优路径(best-track)资料,筛选出西北太平洋地区快速增强和非快速增强两类热带气旋样本。利用美国国家海洋与大气管理局(NOAA)的多平台热带气旋表面风分析资料,对比分析了两类样本的风速和涡度的分布特征。结果显示,快速增强的热带气旋样本通常结构更紧凑,最大风速较大,最大风速半径较小,台风内区的风速较大。在涡度上表现为快速增强热带气旋样本内区的涡度和涡度梯度较大。对两类样本进行t检验,结果显示两类样本内区的切向风差异明显,说明热带气旋的内区风速分布与其发展之间存在密切联系。其物理机制可能是:当存在较大的内区涡度梯度时,涡度隔离机制有利于对流单体向涡旋中心汇聚,此外较大的涡度意味着较大的惯性稳定度,有利于非绝热加热向热带气旋动能的转换,二者共同作用有利于热带气旋的快速发展。

Two categories of tropical cyclone（TC） cases, rapidly intensifying（RI） and non-rapidly intensifying （non-RI） TC cases, are selected according to best-track data from Joint Typhoon Warning Center. Then by using Multiplatform Tropical Cyclone Surface Wind Analysis （MTCSWA） data, different wind speed distribution features and vorticity structure features between RI and non-RI TC cases in the northwest Pacific are analyzed. It is found that there exist significant differences in the TC inner-core structure, Thelarger the compact of TC is, the faster the intensification rate will be. Specifically, the TCs with stronger inner-core vorticity and larger vorticity gradient are more likely to develop rapidly. It is speculated that the larger vorticity gradient of RI cases accelerates convective bursts near the TC to merge through vorticity segregation processes. Meanwhile, greater vorticity implies greater inertial stability, which is helpful for diabatic heating to convert to kinetic energy of TCs. Both of these two factors are conducive to TC development.