Abstract: Using Hilbert transform and NCEP/NCAR reanalysis data, the authors analyze the structures and nature of the long life-cycle baroclinic wave packets in the Southern Hemisphere. The average phase velocity of the carrier wave of wave packets is about 11.2°/d and the average group velocity of wave packets is about 25.4°/d. The vertical structures of wave packets are different at the stages of growth, mature, and decay. During the growing stage, the phase tilting of wave packets westward in the lower troposphere, almost vertical in the middle troposphere, and westward in the upper troposphere. During the mature stage, the phase tilting is westward in the lower troposphere, and the same as that in the growing stage, however, it becomes almost vertical at higher levels. During the decaying stage, the phase of wave packets is vertical at all levels. The time-evolution of wave packet energy is different from one case to another during their life cycles. Some of wave packets experience only one "growth-mature-decay" cycle, but others undergo several such cycles.

Key words: baroclinic wave packets, Hilbert transform

摘要： 利用Hillbert变换和NCEP/NCAR再分析资料，研究南半球夏季长生命期的斜压波包的结构和传播特征。结果表明，波包位相速度平均为11.2°/d，波包的包络传播速度（群速度）平均约为25.4°/d，群速约为相速的2.3倍。波包的位相垂直分布在波包发展阶段、成熟时期和衰减阶段是不同的。在发展阶段，波包位相在对流层低层西倾；对流层低层至高层波包位相随高度是近于垂直的；在对流层高层，其位相又开始西倾。在波包成熟阶段，在对流层低层仍然是西倾，对流层中低层以上其位相近于垂直。在波包衰减阶段，其位相在整个对流层都是近于垂直的。波包传播过程中其能量随时间变化比较复杂。有时波包呈现出一次“增长－成熟－衰减”过程，但有时却呈现出多次“增长－成熟－衰减”过程。

关键词: 斜压波包, Hilbert变换