This paper investigates multiple equilibrium states in the atmosphere, focusing on the effects of topography and thermal forcing on large-scale zonal flows. Using a barotropic channel model, the authors show that multiple stable equilibrium states can exist for a given external driving force. Two types of equilibria are identified: a "low-index" flow with strong wave components and a "high-index" flow with stronger zonal components. The phenomenon of blocking is suggested to be a metastable equilibrium state of the low-index, near-resonant character. The study confirms the existence of these equilibria through numerical integration of a grid-point model with more degrees of freedom than the spectral model. It is found that oscillations can occur when one equilibrium state is stable for the lowest order spectral components but unstable for the next higher order components. These oscillations are attributed to a barotropic instability of the topographic wave, as discussed by Lorenz and Gill. Thermal forcing also produces multiple, stable equilibria in a spectral model, although confirmation with a grid-point model has not yet been obtained. The paper discusses the implications of multiple equilibria for atmospheric phenomena, suggesting that the persistence of large amplitude flow anomalies, such as blocking, may be explained by the existence of multiple stationary or oscillatory equilibrium states. The study also highlights the importance of nonlinear interactions in the atmosphere, particularly in the context of topographic and thermal forcing. The results suggest that the atmosphere can exhibit complex behavior, with multiple stable states and transitions between them. The findings have implications for understanding large-scale atmospheric variability, predictability, and climate.This paper investigates multiple equilibrium states in the atmosphere, focusing on the effects of topography and thermal forcing on large-scale zonal flows. Using a barotropic channel model, the authors show that multiple stable equilibrium states can exist for a given external driving force. Two types of equilibria are identified: a "low-index" flow with strong wave components and a "high-index" flow with stronger zonal components. The phenomenon of blocking is suggested to be a metastable equilibrium state of the low-index, near-resonant character. The study confirms the existence of these equilibria through numerical integration of a grid-point model with more degrees of freedom than the spectral model. It is found that oscillations can occur when one equilibrium state is stable for the lowest order spectral components but unstable for the next higher order components. These oscillations are attributed to a barotropic instability of the topographic wave, as discussed by Lorenz and Gill. Thermal forcing also produces multiple, stable equilibria in a spectral model, although confirmation with a grid-point model has not yet been obtained. The paper discusses the implications of multiple equilibria for atmospheric phenomena, suggesting that the persistence of large amplitude flow anomalies, such as blocking, may be explained by the existence of multiple stationary or oscillatory equilibrium states. The study also highlights the importance of nonlinear interactions in the atmosphere, particularly in the context of topographic and thermal forcing. The results suggest that the atmosphere can exhibit complex behavior, with multiple stable states and transitions between them. The findings have implications for understanding large-scale atmospheric variability, predictability, and climate.