Based on nonlinear modeling studies of growth of baroclinic waves from the most unstable normal mode initial conditions, it had been concluded that these waves mainly grow by baroclinic conversion from mean flow available potential energy, and frequently wave decay is due to barotropic energy conversion from eddy kinetic energy to mean flow kinetic energy, after the wave has driven a strong barotropic jet due to convergence of eddy momentum fluxes. Studies of zonal mean energetics provided some support for this view. However, studies of energetics lifecycles of individual troughs and ridges have suggested that zonal energy (and wave activity) transfer from mature waves to growing waves often dominate over baroclinic and barotropic energy conversion during the growth and decay stages of individual baroclinic waves. This study attempts to reconcile these two apparently contradictory results.

Recent studies have shown that baroclinic waves are frequently organized into wave packets which last much longer than individual troughs or ridges. By tracking these wave packets and computing energy budgets following these wave packets, it is found that wave packets growth generally occurs due to enhanced baroclinic conversion and suppressed barotropic conversion, while wave packet decays frequently because of enhanced barotropic conversion and reduced baroclinic conversion. Thus to certain extent, the baroclinic growth/barotropic decay paradigm is much more appropriate when applied to describe the lifecycle of wave packets than that of individual trough/ridge systems.

In this paper, the energy budget of wave packets will be discussed, and the evolution of a generic wave packet will be contrasted with wave packet evolution under different mean flow conditions.