Abstract
The El Niño/Southern Oscillation (ENSO) is the dominant mode of climate variability affecting worldwide extreme weather events; therefore, improving ENSO prediction is an important issue. In this regard, a peculiar time evolution of ENSO in 2014 posed a challenge to the climate science community. Despite the observance of several precursors for a strong El Niño to develop during the summer and autumn, cold sea surface temperature (SST) anomalies appeared unexpectedly to the south of the equatorial cold tongue, which prevented development of an El Niño event in the late summer. Several hypotheses have been raised to explain the unmaterialized El Niño in 2014, but complete understanding of processes responsible for terminating this event has not yet been obtained. Here we show, using observations and extended seasonal prediction experiments with a climate model, that cold off-equatorial subsurface water in the South Pacific Ocean penetrated into the equatorial region along the slanted isopycnal surface via the mean advection, and it prevented the El Niño evolution in 2014. The negative subsurface temperature anomalies in the off-equatorial South Pacific Ocean were persistent throughout the last decade, and additional numerical simulations indicated that they contributed to the suppression of El Niño events during the 2000s.
Highlights
The El Niño/Southern Oscillation (ENSO) is the dominant mode of climate variability affecting worldwide extreme weather events; improving ENSO prediction is an important issue
We investigated the role of the South Pacific subsurface anomalies in this event based on a one-year prediction of our climate model initialized on 1 November 2013 that reproduced the termination of El Niño in 2014 and an additional sensitivity experiment in which the penetration of South Pacific anomalies into the equatorial region was blocked
We examined a common feature in the Pacific Ocean between the observation and the MIROC5 forecast and found a noteworthy aspect in the lower part of thermocline, which is represented as the
Summary
The El Niño/Southern Oscillation (ENSO) is the dominant mode of climate variability affecting worldwide extreme weather events; improving ENSO prediction is an important issue. We show, using observations and extended seasonal prediction experiments with a climate model, that cold off-equatorial subsurface water in the South Pacific Ocean penetrated into the equatorial region along the slanted isopycnal surface via the mean advection, and it prevented the El Niño evolution in 2014. We investigated the role of the South Pacific subsurface anomalies in this event based on a one-year prediction of our climate model initialized on 1 November 2013 that reproduced the termination of El Niño in 2014 and an additional sensitivity experiment in which the penetration of South Pacific anomalies into the equatorial region was blocked. Using long-term observations and extended model simulations, we investigated the origin of the South Pacific subsurface anomalies
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