Diagnosing the impact of stratospheric planetary wave breaking in a linear model

In the past, linear quasigeostrophic theory has proven successful in modeling the vertical and meridional propagation of stationary planetary waves in the stratosphere. Since in such models the wave solution does not sensitively depend on the wave damping, the latter was usually implemented as relaxation with a simple damping coefficient. As far as the damping is concerned, this is likely to be unrealistic, since it does not account for the locally enhanced dissipation arising from stratospheric Rossby wave breaking. In the present study, a parameterization for Rossby wave breaking (Garcia) is applied to obtain an improved representation of wave damping throughout the stratosphere. Although solving for the wave turns into a nonlinear problem, the model remains linear in the sense that both the basic-state zonal wind and the wave at the tropopause level are specified and kept fixed. The divergence of the Eliassen-Palm flux and the steady-state residual circulation are computed in order to diagnose the impact of the waves on the mean flow. Both quantities depend sensitively and in a complex manner on the given basic-state zonal flow. The model is applied to different scenarios representing the different phases of an idealized quasi-biennial oscillation (QBO). The dependence of the wave forcing on the phase of the QBO is consistent with results from previous studies. The current model allows a clear attribution of differences in wave-mean-flow interaction to differences in the basic flow.