Planetary Wave Coupling - Obervations and Theory

Abstract

Research on the forcing of atmospheric planetary waves, their propagation, their interactions with the mean zonal flow, and their influence on ozone transport is reviewed. Previous GCM and idealized modeling work on the forcing mechanisms for extratropical planetary waves in the troposphere and middle atmosphere has given contradictory results. Some studies indicate that orographic forcing is dominant while others have indicated that the forcing from diabatic heating is at least of equal importance. Some analyses of observed planetary wave structures support the latter view. The evolution of planetary wave propagation from the pioneering work of Chamey and Drazin is reviewed. In particular, the question of whether zero wind lines absorb or reflect is emphasized. It is argued that observational evidence shows signatures of both behaviors. The conditions for planetary wave noninteraction are briefly discussed, and some observations are shown indicating that in the Southern Hemisphere, the relatively small size of the planetary wave forcing leads to the situation where planetary waves reach their largest amplitudes during the equinox seasons whereas in the Northern Hemisphere the planetary waves have their largest amplitudes in winter. The results of some modeling and theoretical work relevant to this interhemispheric difference in planetary waves are reviewed. Finally, it is argued that planetary wave behavior determines the difference in the ozone transport between the Northern and Southern Hemispheres. In particular, since planetary wavenumber 1 is dominant in this regard, the ozone transport behavior generally follows that of wavenumber 1.