Equatorial forcing of interannual Rossby waves in the eastern South Pacific

Abstract

Long baroclinic Rossby waves generated along the western coasts of continents play an important role in transferring coastal perturbations westwards into the ocean's interior. To investigate interannual Rossby waves in the eastern South Pacific (10°S to 40°S), combined TOPEX/ POSEIDON and ERS-1/2 satellite altimeter data were compared with model simulations of Rossby waves for the 1992-2000 period. The multimode linear model includes dissipation and was forced by observed wind stress curl from ERS-1/2 and coastal pycnocline-depth anomalies. The latter were determined by a high-resolution eastern boundary linear model initialized by observed sea level at the equator. Strong westward propagation of pycnocline anomalies originating at the coast can be observed at least as far south as 40°S. The results suggest that an important part of the interannual midlatitude, free baroclinic Rossby waves originated at the coast were forced by pycnocline fluctuations originating from the equator in 1992-2000, a period which was dominated by the 1997-98 El Niño event.