The transmission and transformation of baroclinic Rossby waves by topography

The transmission of westward propagating baroclinic Rossby waves incident o n a gappy meridional barrier is studied in the context of the two-layer, qu asigeostrophic model. The meridional barrier models the presence of very st eep topography such as the midocean ridge system or extensive island arcs. The nature of the transmission depends strongly on the nature of the gaps i n the meridional barrier. If the gaps extend throughout the depth of the fl uid, the Rossby waves propagate through the barrier, as a consequence of Ke lvin'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, t here is a significant transformation of the vertical structure of the wave field as it traverses the barrier. In particular, waves of baroclinic verti cal structure in the model are transformed on the western side of the barri er into barotropic waves that radiate from the segment of the barrier betwe en two such gaps. Such segments act as antennae radiating barotropic energy into the western subbasin. It is suggested that recent observations of sig nal 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 mode s in closed basins are described.