On Energy Flux and Group Velocity of Waves in Baroclinic Flows

A modified energy flux is defined by adding a nondivergent term that involves β to the traditional energy flux. The resultant flux, when normalized by the total eddy energy, is exactly equal to the group velocity of Rossby waves on a β plane with constant zonal flow. In this study, we computed the normalized energy flux for linear wave packets in baroclinic basic states with different vertical profiles. The results show that the normalized energy flux is a good approximation to the group velocity of all parts of the wave packet for the basic states examined. The extension to the nonlinear case is briefly discussed. The magnitude of the fluxes of a downstream developing wave group over the wintertime northern Pacific storm track defined by a regression analysis is computed, and the group velocity defined by the energy fluxes is found to be comparable to the group velocity of propagation of the observed wave packet. The results indicate a very strong component of downstream energy radiation, suggesting that downstream energy dispersion is very important in the evolution of waves in the storm track.