Equilibration in an eddy resolving model with simplified physics

The role of waves in maintaining the midlatitude tropospheric climate is in vestigated in a dry high-resolution quasigeostrophic beta -plane channel mo del coupled to both a simplified model of the atmospheric boundary layer an d an interactive static stability. The climate of the model's equilibrated state is found to be separated into two dynamical regimes, one within the boundary layer and the other within the free troposphere. Thermal diffusion in the atmospheric boundary layer p revents the eddies from modifying the mean temperature structure there by d amping temperature fluctuations. The potential vorticity gradients are esse ntially eliminated in the lower troposphere above the boundary layer, in ag reement with observations. The homogenization of potential vorticity occurs in the region where the baroclinic waves have a critical layer, and is acc omplished mainly by an increase in the static stability in the lower tropos phere due to the vertical eddy heat fluxes. Even though the model has kinetic energy and enstrophy spectra characterist ic of a fully turbulent flow, the equilibrated state of the model is essent ially maintained by wave-mean flow interaction, primarily by the interactio n between wave 5 and the zonal mean state. The zonal mean of the equilibrat ed state is found to be linearly stable to all waves. The largest-scale wav e in the fully nonlinear state, wave 4, is found to be maintained by an ene rgy cascade from the higher wavenumbers. However when wave 4 is large, stab ility analysis indicates that it is unstable, with the growing mode dominat ed by wave 6. This instability appears to saturate quickly and hand its ene rgy over to wave 5. The result is that the amplitude of waves 4 and 5 in th e equilibrated state are strongly anticorrelated, but the fluctuations in t otal eddy kinetic energy are strongly correlated with the fluctuations in t he sum of the energy in waves 4 and 5.