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OUT OF THIS WORLD | Earth, Space And The Stuff In Between - a daily journey through weather, space and science with meteorologist/science writer Scott Sutherland

El Niño Update: Could it be gaining a second wind?

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Scott Sutherland
Meteorologist/Science Writer

Sunday, January 24, 2016, 10:33 - Eyes are still on El Nino this month, as it gives more indications of having reached peak levels, however are new signs pointing towards a fresh surge in strength?

As we reached the end of 2015, the most up-to-date look at the El Niño pattern in the equatorial Pacific Ocean showed that temperatures in the central equatorial Pacific -  the "Niño 3.4 region" which scientists use to gauge the strength of the El Niño Southern Oscillation (ENSO) - had reached their maximum in mid November, and were slowly cooling down.

The latest look from NASA appears to support that conclusion. As they wrote on the NASA Earth Observatory website:

If past events help predict future ones, then we have probably reached the peak of the 2015–2016 El Niño. Warmer-than-average waters in the eastern tropical Pacific Ocean should start to cool off and shift westward. By summer, the tropical Pacific might be back in a neutral state or La Niña cooling could kick in, as it did after major El Niños of the past.

However, although representations of the pattern usually focus on sea surface heights and temperatures, that is only because it is usually the easiest way to visualize what's happening.


Tracking sea surface heights with NASA's Jason-2 satellite. Credit: NASA Earth Observatory/Joshua Stevens


Sea surface temperature anomalies across the Pacific Ocean, from October 28, 2015 to January 13, 2016. Credit: NOAA

The fact is, the ocean is only one half of ENSO, and to get a complete picture of what's going on, the atmosphere over the equatorial Pacific needs to be taken into account as well.

While the general strength of an El Niño is recorded with the Oceanic Niño Index (ONI), the Southern Oscillation Index (SOI) is used to track what is happening with the atmosphere.

Just like ONI, the SOI is a three-month running average, but in this case, rather than tracking temperatures above or below normal in one region of the ocean, SOI tracks the difference in atmospheric pressure between two places - Tahiti, in the middle of the Pacific, and Darwin, in northern Australia.


Credit: NOAA Climate.gov/Fiona Martin.

As we progressed through 2015, ONI values continued to climb, reaching a maximum of +2.3 for the October-December three-month average, and matching the strength of the 1997-98 "super" El Niño in the process

At the same time, weekly sea surface temperature anomalies in the Niño 3.4 region reached a peak in mid-November, at their highest level ever seen - 5.58oF above normal (they only reached a maximum of +5.04oF in 1997). By now, a few weeks into 2016, sea surface temperature (SST) anomalies in the central Pacific continued on a slow downward tend, having reached +4.68oF above normal, but the SOI is very different.

When sea surface temperatures were on the rise in the central Pacific, SOI values were getting more and more negative - indicating a strengthening El Niño - with higher atmospheric pressure over northern Australia than over the central Pacific, and thus weaker trade winds and the spreading of warmer waters towards the east. Then, in December, the SOI backed off, apparently matching the weakening trend seen in the ocean after the November peak.

In the last days of 2015 and in first few weeks of 2016, however, there has been a surge in the SOI, driving it strongly negative.

As of January 22, 2016, the SOI has reached a 30-day average value of -20.48 (anything -8 or lower indicates El Niño conditions, and anything below -20 for any significant amount of time gets in the "super" El Niño range).

What could this mean for us in 2016?

According to NASA's Earth Observatory, this shift in the SOI was not missed by scientists monitoring the pattern:

Bill Patzert, a climatologist at NASA’s Jet Propulsion Laboratory, sees the potential for a second peak for this El Niño. He pointed to a recent relaxation in the trade winds and a west wind burst that could refuel the warming trend in the eastern Pacific. Weaker trade winds in the eastern Pacific allow west wind bursts to push warm waters toward the Americas. Patzert suspects February and March 2016 could still be very active months for El Niño-driven weather along the western coasts of the Americas.

As 2015 has now taken its place as the new hottest year on record, with an over 99 per cent confidence level from NOAA, El Niño definitely played a roll in that. The influence wasn't overwhelming, as NASA climate scientist Gavin Schmidt estimated that it added 0.13oF to the global temperature anomalies for the year.

There is an overall trend, however. Look at the nine El Niño events going back into the 80s, and for all but two - 1991-92 and 2006-07 - the second year of the event was the hotter one.

This reached an extreme case for the last super El Nino, too, in 1997-98. 1997 took the top spot on the list of hottest years on record after the year was over, at 0.912oF over the 20th century average, but it only held that spot for one year. 1998 came in at over a tenth of a degree hotter than that when all the numbers were tallied (and +1.13oF above the 20th century average). It was so warm that year that it set a kind of "new normal" for the world, and that year maintained the #1 position on the list of hottest years until 2005 came along. Since at least the 1970s, that's the longest any year has held the top spot on that list.


NOAA's hottest years on record going back to 1975, with notations by S. Sutherland

Will 2016 do the same - becoming the new hottest year on record and setting yet another new standard for global temperatures? Stay tuned for some more in-depth analysis to come

Sources: NASA Earth Observatory | NOAA | NOAA | Queensland Government

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