Wind‐driven interdecadal variability in the eastern tropical and South Pacific

Abstract

Simulated interface elevation anomalies with a reduced gravity model forced by observed wind stress are used to investigate the origin of thermocline depth fluctuations in the eastern tropical and South Pacific at interdecadal timescales. It is found that interdecadal thermocline depth fluctuations in the eastern equatorial Pacific and along the western coast of the Americas are fundamentally driven by zonal wind fluctuations in the western equatorial Pacific. Thus positive (negative) interface elevation anomalies, which correspond to shallower (deeper) thermocline depths, in the eastern tropical Pacific and along the west coast of Central and South America are related to easterly (westerly) anomalies in the western sector of the equatorial Pacific. However, off‐equatorial wind fluctuations maintain and reinforce the interdecadal variability observed along the eastern equatorial Pacific and along the west coast of South America. In the latter region, equatorial (off‐equatorial) wind forcing is relatively more important equatorward (poleward) of 30°S. In the eastern equatorial Pacific, interface elevation anomalies are negatively correlated with sea surface temperature (SST) at interdecadal timescales. According to our results the SST interdecadal anomalies are in part (50–60%) driven by wind fluctuations likely through the modulation of vertical advection of cold waters which depends primarily on the thermocline depth forced remotely or locally by winds. This relationship was especially strong during the 1970s and 1980s, a period characterized by the larger zonal wind stress interdecadal fluctuations observed in the western equatorial Pacific.