On the resonance of an external planetary wave and its interaction with the mean zonal flow

Abstract

Numerical experiments are performed to examine the resonant growth of a topographically forced wave in a nonlinear model. Time-dependent simulations are made including damping mechanisms, wave-mean flow interactions, a zonal wind driving force and wave-wave interactions. The initial mean zonal wind permits the resonance of the barotropic mode, rather than the first internal mode as in a previous study. It is found that even when damping and nonlinear interactions are included, the growth rate and the amplitude achieved by the resonant barotropic wave are similar to those occurring in observed planetary wave amplification episodes, such as those seen in some developing blocking conditions. Eliassen-Palm flux cross-sections of one of the integrations are presented to illustrate the interaction between the forced wave and the mean zonal flow.