Barotropic decay of baroclinic waves in a two-layer beta-plane model

If the shear is sufficiently weak, the wave undergoes periodic amplitude vacillation characterized by symmetric baroclinic growth and baroclinic decay. However, when the meridional shear is strong enough to allow for the existence of a critical layer, the flow undergoes an asymmetric life cycle which resembles that found by Simmons and Hoskins in a primitive equation model on the sphere: the wave grows baroclinically but decays barotropically toward a wave-free state. Throughout the barotropic decay stage, the wave is breaking and being absorbed either at or before the critical layer. -from Authors