Laterally forced equatorial perturbations in a linear model. Part II: mobile forcing

An analytical solution of the model with a constant mean zonal flow reveals that amplitudes of forced waves can be significantly modulated by the mean zonal flow through its Doppler-shift effect on the forcing frequency. In general, amplitudes of westward-propagating waves, such as the Rossby and mixed Rossby-gravity waves, tend to be larger in mean westerlies than in mean easterlies for low-frequency forcing but smaller in mean westerlies for high-frequency forcing. The opposite dependence on the mean zonal flow applies to eastward-propagating waves, such as the Kelvin wave. The model numerical solutions show that the spatial structure of the laterally forced equatorial perturbation as a whole is sensitive to the mean zonal flow. -from Author