ON ENERGY FLUX AND GROUP-VELOCITY OF WAVES IN BAROCLINIC FLOWS

A modified energy flux is defined by adding a nondivergent term that i nvolves beta to the traditional energy flux. The resultant flux, when normalized by the total eddy energy, is exactly equal to the group vel ocity of Rossby waves on a beta plane with constant zonal flow. In thi s study, we computed the normalized energy flux for linear wave packet s in baroclinic basic states with different vertical profiles. The res ults show that the normalized energy flux is a good approximation to t he group velocity of all parts of the wave packet for the basic states examined. The extension to the nonlinear case is briefly discussed. T he magnitude of the fluxes of a downstream developing wave group over the wintertime northern Pacific storm track defined by a regression an alysis is computed, and the group velocity defined by the energy fluxe s is found to be comparable to the group velocity of propagation of th e observed wave packet. The results indicate a very strong component o f downstream energy radiation, suggesting that downstream energy dispe rsion is very important in the evolution of waves in the storm track.