The northeast Pacific Ocean response to the 1982–1983 El Niño

Abstract

The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982–1983 El Niño. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982–1983 El Niño. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large‐scale atmosphere, while along the California coast and south to the equator, the dominant El Niño signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western equatorial Pacific Ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50°N using data from two reduced gravity, primitive equation models coupled at 18°N. At shorter, seasonal time scales, the acceleration of the wind appears to be an important mechanism in driving coastal currents.