The paper by J. G. Charney investigates the dynamics of long waves in a baroclinic westerly current. Previous studies of long-wave perturbations in the free atmosphere have often neglected vertical shear in the zonal current or variations in the vertical component of Earth's angular velocity. Charney's work addresses these shortcomings by incorporating both elements, leading to a more accurate solution that aligns with observed atmospheric behavior. By eliminating acoustic and shearing-gravitational oscillations, Charney reduces the perturbation equations to a solvable system. He deduces exact stability criteria, showing that instability increases with shear, lapse rate, and latitude, and decreases with wave length. Application of these criteria to seasonal zonal wind averages suggests that the middle-latitude westerlies are a region of constant dynamic instability. Unstable waves are similar to observed perturbations, with eastward propagation speeds close to the surface zonal current. These waves exhibit thermal asymmetry and a westward tilt with height. In the lower troposphere, maximum positive vertical velocities occur between the trough and the nodal line to the east in the pressure field. The distribution of horizontal mass divergence is calculated, showing that the concept of a fixed level of nondivergence must be replaced by a sloping surface of nondivergence. Charney generalizes the Rossby formula for barotropic wave speed to a baroclinic atmosphere, showing that the barotropic formula holds if the constant zonal wind is that observed near 600 mb. The paper discusses the structure of waves, showing that neutral and unstable waves differ in their velocity fields and phase relationships with pressure and density fields. The presence of instability leads to thermal asymmetry and a westward tilt of the wave pattern with height. The wave velocity is determined by the balance of forces, and the stability criteria are derived from the wave equations. The paper also addresses the application of the theory to the tropical easterlies, showing that the stability criteria are qualitatively similar to those for the westerlies, but with differences when the normal meridional temperature gradient is reversed. The atmospheric model used assumes a zonal flow with a linear increase in zonal wind with height in the troposphere and a constant zonal wind in the stratosphere. The model is consistent with observed mean states of the atmosphere, particularly at low levels. The fundamental equations of motion are derived, and the boundary conditions are formulated for a compressible atmosphere. The equations are linearized for small perturbations, leading to a solution in the form of sinusoidal waves. The wave velocity is determined by the balance of forces, and the stability criteria are derived from the wave equations. The paper concludes that the baroclinic wave model exhibits many characteristics of waves observed on weather maps, including speed of propagation and internal structure. The theory predicts that waves of length less than 6000 km will be unstable when the vertical shearThe paper by J. G. Charney investigates the dynamics of long waves in a baroclinic westerly current. Previous studies of long-wave perturbations in the free atmosphere have often neglected vertical shear in the zonal current or variations in the vertical component of Earth's angular velocity. Charney's work addresses these shortcomings by incorporating both elements, leading to a more accurate solution that aligns with observed atmospheric behavior. By eliminating acoustic and shearing-gravitational oscillations, Charney reduces the perturbation equations to a solvable system. He deduces exact stability criteria, showing that instability increases with shear, lapse rate, and latitude, and decreases with wave length. Application of these criteria to seasonal zonal wind averages suggests that the middle-latitude westerlies are a region of constant dynamic instability. Unstable waves are similar to observed perturbations, with eastward propagation speeds close to the surface zonal current. These waves exhibit thermal asymmetry and a westward tilt with height. In the lower troposphere, maximum positive vertical velocities occur between the trough and the nodal line to the east in the pressure field. The distribution of horizontal mass divergence is calculated, showing that the concept of a fixed level of nondivergence must be replaced by a sloping surface of nondivergence. Charney generalizes the Rossby formula for barotropic wave speed to a baroclinic atmosphere, showing that the barotropic formula holds if the constant zonal wind is that observed near 600 mb. The paper discusses the structure of waves, showing that neutral and unstable waves differ in their velocity fields and phase relationships with pressure and density fields. The presence of instability leads to thermal asymmetry and a westward tilt of the wave pattern with height. The wave velocity is determined by the balance of forces, and the stability criteria are derived from the wave equations. The paper also addresses the application of the theory to the tropical easterlies, showing that the stability criteria are qualitatively similar to those for the westerlies, but with differences when the normal meridional temperature gradient is reversed. The atmospheric model used assumes a zonal flow with a linear increase in zonal wind with height in the troposphere and a constant zonal wind in the stratosphere. The model is consistent with observed mean states of the atmosphere, particularly at low levels. The fundamental equations of motion are derived, and the boundary conditions are formulated for a compressible atmosphere. The equations are linearized for small perturbations, leading to a solution in the form of sinusoidal waves. The wave velocity is determined by the balance of forces, and the stability criteria are derived from the wave equations. The paper concludes that the baroclinic wave model exhibits many characteristics of waves observed on weather maps, including speed of propagation and internal structure. The theory predicts that waves of length less than 6000 km will be unstable when the vertical shear