Dynamical Aspects of the General Circulation and the Stability of Zonal Flow

From solutions of the linearized vorticity equation applied to systems with a variable basic zonal current, it is shown that the effect of damped disturbances is to feed energy into the zonal flow and transfer angular momentum from zones of easterlies into zones of westerlies, thereby strengthening the zonal circulation of the atmosphere. Amplifying disturbances withdraw energy from the zonal flow and transfer angular momentum from zones of westerlies into zones of easterlies, thereby weakening the strong zonal circulation and transforming it into cellular vortex motions. Thus the migratory cyclones and anticyclones are necessary elements for developing and maintaining the zonal circulation, while, on the other hand, they also act occasionally as brakes on the general circulation, keeping it from growing indefinitely. The neutral disturbance corresponding to a typical zonal wind profile in winter is investigated by numerical integration. The stream line pattern is found to be rather similar to a typical flow pattern in the upper troposphere during a period of little change, indicating that this flow pattern is associated with the nearly neutral or slightly damped oscillations. DOI: 10.1111/j.2153-3490.1951.tb00809.x