Most El Niños since 1958 began with a previously unidentified subsurface discharge of warm water about 18 months before the peak of the events
By Summit Voice
SUMMIT COUNTY — Not every El Niño is the same, but all of them start with a massive discharge of sub-surface warm water from the equatorial western Pacific.
That discharge starts much earlier than previously recognized, and may provide an early warning for the onset of El Niños, which can affect much of the world with weather anomalies, including flooding rains in some places and drought in other areas. It’s also seen as a mechanism for recharging the tropics with warm water.
The new El Niño study was authored by Nandini Ramesh and Raghu Murtugudd, associated with the University of New South Wales Climate Change Research Centre and published in the journal Nature Climate Change.
The scientists studied El Niño episodes between 1958 and 2011 to try and find a pattern. In the process, they showed that El Niños in the 1980s and 1990s started with warm sea surface temperature anomalies near the dateline that spread eastward, while earlier episodes started with anomalies off the west coast of South America and spread to the west.
Another spatial variation has prevailed since 2000, with warm anomalies in the central Pacific rather than the eastern upwelling region. In their paper, the researchers say that the “apparent absence of any unchanging component in the development of ENSO events through regimes implies that we may not understand some fundamental aspects of the system.”
But the new study may start to change that by showing that the subsurface discharge of warm water always begins in the boreal (northern hemisphere) summer and autumn of the year before the La Niña event, up to 18 months before the peak. The study concludes that the deep water discharge is fundamental to the onset of El Niño.
The researchers said the sub-surface discharge hadn’t previously been identified because
This sub-surface process had not been noticed before because the discharge of warm water is not easy to detect using satellite measurements.
Up to now, long-range predictions for El Niños have only been reliable about six months in advance, but followup studies could help improve that forecasting skill