Stable Near-Resonant States Forced by Perturbation Heating in a Simple Baroclinic Model

Abstract

The stationary nonlinear response to perturbation heating is calculated in a highly truncated, two-level baroclinic model. For certain values of the intrinsic parameters and forcing, multiple equilibrium states exist. For a specific zonal and meridional wavelength, three equilibrium states are present: two are near a resonant point and one is near the zonal forcing equilibrium. Only one of these is ever stable, namely, the one where the zonal wind is on the low side of the resonant point; this state has a relatively small zonal wind and relatively large stationary perturbations. The equilibrium point on the high side of resonance is unstable mainly due to resonant instability and the equilibrium point near the forcing equilibrium is unstable mainly due to baroclinic unstability. Different equilibria are obtained for each vector wavenumber because the resonant value of the zonal wind decreases with decreasing wavelength.