Abstract

Anomalous April–June warm surface water in the eastern Pacific convergence zone (the Great Pacific Garbage Patch) subducts and depresses the thermocline as a single waveform. This waveform propagates toward the equator much more quickly (reaching the equator in 1.5–2.5 years) than the normal transit time (5–10 years) of the meridional overturning cell. The movements of the sea-surface temperature (SST) anomalies that occurred before the 1997 and 2009 El Niños can be clearly traced to the area south of 20°N using the altimeter sea-level signals. Upon arriving near the Pacific equator, these warm water anomalies can contribute to the formation of the El Niño by lowering the depth of the thermocline. The time required for a subducted SST anomaly to "drift" 3000 km to the equator depends upon its initial location and on the distribution of the SST anomalies near the western coast of North America. The subducted warm SST anomalies observed before the El Niños of 1982 and 1997 took 12 months to reach the equator. Longer drift times of 24 months were indicated for the 1972, 1986, 1993, 2003, 2006 and 2009 events. The thermocline depressions that "drift" toward the equator in the eastern Pacific are shown to be a major energy source for the onset of the El Niño in the central and eastern Pacific. This study presents a theory that could expand our understanding of the onset mechanism of the El Niño episode.

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