The role of coastal Kelvin waves on the northeast Pacific Ocean

Abstract

Kelvin waves excited by the wind in the western equatorial Pacific Ocean propagate eastward to the boundary and then poleward along the coast. Poleward propagating coastal Kelvin waves produce a signal that propagates away from the coast as westward propagating Rossby waves with amplitude proportional to the amplitude of the passing Kelvin wave. The frequency of the Kelvin wave signal sets the frequency of the Rossby response and the possible wavelengths through the Rossby dispersion relation. This paper examines the role of coastal Kelvin waves in the mid-latitude response of the ocean in general, and the mid-latitude 1982–1983 El Niño response in particular, using two primitive equation numerical models of the equatorial and northeast Pacific Oceans. The equatorial model, in agreement with observations, shows a large amplitude Kelvin wave propagating eastward along the equator as a prelude to the 1982–1983 El Niño and then poleward along the coast. A time series of the model coastal signal from 1975 through 1984, extracted from the equatorial model, forces a northeast Pacific Ocean model near the coast at 18° N, allowing signals to propagate from the equator through low-latitudes to mid-latitudes. Model results show, (1) that the coastal Kelvin wave initializes and defines the frequency of the offshore propagating Rossby wave (2) that the Kelvin-Rossby response is fundamental to the development of the mid-latitude 1982–1983 El Niño and, (3) that Rossby waves at 30° N extend the signal seaward from the coast several thousand kilometers, although the Rossby wave signal loses its identity in the region of the California Current several hundred kilometers from the coast.