关键词: 斜压波包, Hilbert变换

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