The paper by Jule G. Charney and John G. DeVore explores the phenomenon of multiple flow equilibria in the atmosphere, particularly focusing on the blocking effect. They use a barotropic channel model to study planetary-scale motions driven by external zonal flow. The model incorporates topographical forcing and thermal forcing to induce perturbations. The authors find that there can be multiple stable equilibrium states for a given driving, with two or more states being metastable. These states include a "low-index" flow with a strong zonal component and a weak wave component, and a "high-index" flow with a weak zonal component and a stronger wave component. The blocking phenomenon is suggested to be a metastable equilibrium state of the low-index, near-resonant type. The existence of these equilibria is confirmed through numerical integration of a grid-point model with more degrees of freedom than the spectral model. The study also reveals that oscillations can occur when one equilibrium state is stable for the lowest order spectral components but unstable for higher-order components, similar to the barotropic instability of topographic waves discussed by Lorenz and Gill. Thermal forcing also produces multiple stable equilibria in a spectral model, though this has not been confirmed with the grid-point model. The authors conclude that the persistence of large-amplitude flow anomalies like blocking is associated with the occurrence of multiple stationary or oscillatory equilibrium states, and that these states can be influenced by nonlinear interactions with topography and asymmetric thermal driving.The paper by Jule G. Charney and John G. DeVore explores the phenomenon of multiple flow equilibria in the atmosphere, particularly focusing on the blocking effect. They use a barotropic channel model to study planetary-scale motions driven by external zonal flow. The model incorporates topographical forcing and thermal forcing to induce perturbations. The authors find that there can be multiple stable equilibrium states for a given driving, with two or more states being metastable. These states include a "low-index" flow with a strong zonal component and a weak wave component, and a "high-index" flow with a weak zonal component and a stronger wave component. The blocking phenomenon is suggested to be a metastable equilibrium state of the low-index, near-resonant type. The existence of these equilibria is confirmed through numerical integration of a grid-point model with more degrees of freedom than the spectral model. The study also reveals that oscillations can occur when one equilibrium state is stable for the lowest order spectral components but unstable for higher-order components, similar to the barotropic instability of topographic waves discussed by Lorenz and Gill. Thermal forcing also produces multiple stable equilibria in a spectral model, though this has not been confirmed with the grid-point model. The authors conclude that the persistence of large-amplitude flow anomalies like blocking is associated with the occurrence of multiple stationary or oscillatory equilibrium states, and that these states can be influenced by nonlinear interactions with topography and asymmetric thermal driving.