The Transmission and Transformation of Baroclinic Rossby Waves by Topography*

The transmission of westward propagating baroclinic Rossby waves incident on a gappy meridional barrier is studied in the context of the two-layer, quasigeostrophic model. The meridional barrier models the presence of very steep topography such as the midocean ridge system or extensive island arcs. The nature of the transmission depends strongly on the nature of the gaps in the meridional barrier. If the gaps extend throughout the depth of the fluid, the Rossby waves propagate through the barrier, as a consequence of Kelvin’s theorem, with no change in vertical structure. On the other hand, if the gaps in the barrier are partial and extend only over a single layer, there is a significant transformation of the vertical structure of the wave field as it traverses the barrier. In particular, waves of baroclinic vertical structure in the model are transformed on the western side of the barrier into barotropic waves that radiate from the segment of the barrier between two such gaps. Such segments act as antennae radiating barotropic energy into the western subbasin. It is suggested that recent observations of signal enhancement of Rossby waves at the midocean ridge system in the Pacific may be related to such transformation of wave structure. The problems of free waves and forced waves in open regions and normal modes in closed basins are described.