VORTICITY TRANSFER AS RELATED TO THE DEVELOPMENT OF THE GENERAL CIRCULATION

Abstract

The mechanism of the development and maintenance of the zonal circulation of the atmosphere is discussed from the point of view of vorticity transfer by atmospheric disturbances. Because the disturbances with vorticity concentrations are unable to stay in equilibrium in a non-uniform field of absolute vorticity, they are displaced by masses of air from other latitudes. These disturbances seek the latitudes where the absolute vorticity equals their own, resulting in a transfer of vorticity against the absolute vorticity gradient. The meridional gradient of vorticity is increased within the region where the disturbances are active and decreased beyond, respectively creating westerly and easterly currents in these regions. The process is also discussed by using harmonic solutions of the vorticity equation. The time required for the creation of strong zonal currents is estimated, and it is found to be of the order of three weeks, agreeing with statistical results. Simple expressions for the distributions of the mean seasonal zonal winds are derived; they fit the observations closely.