Trapped Planetary (Rossby) Waves Observed in the Indian Ocean by Satellite Borne Altimeters
Ocean Science Discussions
Using 20 years of accurately calibrated, high resolution, observations of Sea Surface Height Anomalies (SSHA) by satellite borne altimeters we show that in the Indian Ocean south of the Australian coast the low frequency variations of SSHA are dominated by westward propagating, trapped, i.e. non-harmonic, planetary waves. Our results demonstrate that the meridional-dependent amplitudes of the SSHA are large only within a few degrees of latitude next to the South-Australian coast while
... coast while farther in the ocean they are uniformly small. This meridional variation of the SSHA signal is typical of the amplitude structure in the trapped wave theory. The westward propagation speed of the SSHA signals is analyzed by employing three different methods of estimation. Each one of these methods yields speed estimates that can vary widely between adjacent latitudes but the combination of at least two of the three methods yields much smoother variation. The estimates obtained in this manner show that the observed phase speeds at different latitudes exceed the phase speeds of harmonic Rossby (Planetary) waves by 140&thinsp;% to 200&thinsp;%. In contrast, the theory of trapped Rossby (Planetary) waves in a domain bounded by a wall on its equatorward side yields phase speeds that approximate more closely the observed phase speeds.