UPDATE: Added the initial note. (And I fixed the formatting. Not sure what happened there, but I lost all of the paragraph breaks.)
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And that’s why the 2014/15 El Niño appears so weak…and has disappeared from NOAA’s Oceanic NINO Index with their new ERSST.v4 data. If we look at the tropical Pacific as a whole though, the 2014/15 El Niño was a relatively strong El Niño—stronger than many El Niños during the satellite era. This post reinforces a few of the points made in the December 2014 post Did ENSO and the “Monster” Kelvin Wave Contribute to the Record High Global Sea Surface Temperatures in 2014?
NOAA and other weather agencies around the globe monitor the sea surface temperature anomalies of the NINO3.4 region for numerous reasons. The possible impacts of the variations in NINO3.4 region surface temperatures on surface temperatures and precipitation around the globe are well studied. This post is in no way intended to cast doubt on those studies. The NINO3.4 sea surface temperatures are a very useful ENSO index. This post does show, however, that occasionally we miss things when we define an ENSO event using one metric.
NOAA uses the sea surface temperatures of a portion of the equatorial Pacific to determine the strength of an El Niño and to list that ENSO event on their Oceanic NINO Index, assuming it meets their requirements. That portion is called the NINO3.4 region, which is bordered by the coordinates of 5S-5N, 170W-120W. See the map here. But as we’ve noted a number of times in the 2014/15 El Niño Series posts, the 2014/15 El Niño was not focused on the NINO3.4 region. In fact, of the NINO regions, the NINO3.4 region was least impacted by the El Niño processes…the El Niño blossomed east and west of the NINO3.4 region. We can see this in the Hovmoller diagram of equatorial sea surface temperature anomalies from the NOAA GODAS website for 2014, Figure 1. I’ve highlighted the longitudes of the NINO3.4 region in grey. Figure 1
Let’s drop back a year. As you’ll recall, early in 2014 a huge pocket of warm water from the West Pacific Warm Pool migrated eastward along the Cromwell Current (a subsurface equatorial Pacific current that travels from west to east, also known as the Pacific Equatorial Undercurrent). See the gif animation of the equatorial subsurface temperature anomalies for January through June 2014 here. Alarmists went berserk with all sorts of proclamations, including a “Super El Niño” for 2014/15 (that didn’t develop) and that the unprecedented “monster Kelvin wave” that initiated the El Niño was fueled by anthropogenic global warming (which we dispelled by showing that the ocean heat content of the tropical Pacific was lower leading into 2014 than it was before the 1997/98 El Niño. See the post The 2014/15 El Niño – Part 2 – The Alarmist Misinformation (BS) Begins.).
Alarmists have short memories… conveniently short. (Recalling their failed predictions would take all of the fun out of alarmism.) When the Super El Niño failed to form later in the year, and when the sea surface temperatures in the NINO3.4 region did not even qualify to be registered as an El Niño in NOAA’s Oceanic NINO Index until April of this year, the alarmists forgot all about all of that naturally (sunlight-) created warm water that had migrated to the east earlier in 2014. To alarmists, the elevated surface temperatures in 2014 were no longer associated with the warm water associated with that “monster” Kelvin wave. But in the real world, that warm water didn’t just disappear…only from the memories of alarmists.
NOTE: As we discussed a few days ago in the post Weak El Niños and La Niñas Come and Go from NOAA’s Oceanic NINO Index (ONI) with Each SST Dataset Revision, in April 2015, NOAA listed the 2014/15 El Niño on its Oceanic NINO Index (the ONI based on their ERSST.v3b data), but two months later, with the release of NOAA’s ERSST.v4 data, the 2014/15 El Niño has dropped off of the present Oceanic NINO Index. [End note.]
WHERE DID ALL OF THAT WARM WATER GO THAT’S ASSOCIATED WITH THE ALARMISTS’ “MONSTER” KELVIN WAVE?
The warm water that had travelled east early in 2014 had to go somewhere. As illustrated above in Figure 1, some of the warm water upwelled to the surface east and west of the NINO3.4 region along the equatorial Pacific. Thus, the goings on in the NINO3.4 region hardly showed up in a graph of the sea surface temperature anomalies there, Figure 2. Figure 2
According to interviews with Kevin Trenberth and Axel Timmerman in the November 2014 article Warming Pacific Drives Global Temperature at ReportingClimateScience, some of the warm water migrated poleward along the west coasts of the Americas:
Next, a series of waves of warm water – known as Kelvin waves – moved across the Pacific from the west near Indonesia to the east and these were interpreted as signs that an El Nino Pacific Ocean warming event may be about to take place. Trenberth explained to reportingclimatescience.com that, as a result of this movement of water, sea levels rose in the central and eastern Pacific and fell back in the western Pacific. However, this warm water did not trigger the expected full blown El Nino. Instead, the warm water moved across the Pacific until it hit the western coast of the Americas and moved north and south – warming coastal waters along the west coast of North America as far north as Oregon and causing a warming of the north eastern Pacific Ocean waters from April through to September.
We further discussed those Coastally Trapped Kelvin Waves in the post Axel Timmermann and Kevin Trenberth Highlight the Importance of Natural Variability in Global Warming…
Some of the warm water from the initial Kelvin wave in 2014 broke away from the equator and was recirculated west, where it helped supply the warm water for a second, less powerful downwelling (warm) Kelvin wave in 2014. That secondary downwelling Kelvin wave helped raise the sea surface temperature anomalies of the equatorial Pacific again toward the end of last year. We first presented this peculiarity in the July 2014 post The 2014/15 El Niño – Part 14 – Warm Water Recirculated?
And last, but not least, we can look at the sea surface temperature anomalies of the tropical Pacific as a whole, Figure 3, and see something entirely different than the data for the NINO3.4 region (Figure 2 above). We’re using the coordinates of 24S-24N, 120E-80W for the tropical Pacific. There appears to have been a very noticeable warming event in tropical Pacific in 2014. This suggests that part of the warm water from the Kelvin waves was simply distributed throughout the tropical Pacific…instead of remaining focused on the equator. Figure 3
And just in case you’re concerned about the minor trend of less than +0.03 deg C/decade over the past 3+ decades, the sea surface temperature anomalies for the tropical Pacific have been detrended in Figure 4. The warming event—a tropical Pacific-wide El Niño?—is still very noticeable. Figure 4
LET’S COMPARE THE EVOLUTION OF THE 2014/15 EVENT IN THE TROPICAL PACIFIC (AS A WHOLE) TO THE OTHER EL NIÑOS OF THE SATELLITE ERA
For the rest of the post, we’ll be presenting the detrended sea surface temperature anomalies of the tropical Pacific. We’re also using NOAA’s Oceanic NINO Index to determine which events were El Niños.
We’ll start with comparisons of tropical Pacific temperature anomalies (detrended) during the evolutions of the strong El Niño events of 1982/83, 1997/98 and 2009/10. See Figure 5. There’s no comparing the evolution of the 2014/15 event (or the others) to the 1997/98 event. The 1997/98 event was in a league of its own. The 2014/15 event, however, ended the year weaker than the 1982/83 and 2009/10 events, but the evolution of the 2014/15 event was stronger than the 1982/83 El Niño for much of their respective years. Figure 5
The only other multiyear El Niño during the satellite era was the 1986/87/88 El Niño. See Figure 6. The 1st year evolution of the event in 2014 was much stronger than in 1986 based on the detrended data for the tropical Pacific, and the second year of the current event (2015) is much stronger than 1987. Figure 6
Next up in Figure 7 are the 2002/03, 2004/05 and 2006/07 El Niños along with the 2014/15 event. Based on the detrended data for the tropical Pacific, they all evolved differently, but the 2014 evolution peaked near the values of the others late in their respective years. From May to October, however, the 2014 event was stronger than the evolution of the 2002/03 El Niño. And from April to November, 2014 was definitely stronger than the 2004/05 and 2006/07 events. Figure 7
Last are the 1991/92 and 1994/95 El Niños. See Figure 8. From April on, based on the detrended sea surface temperature anomalies of the tropical Pacific, the evolution of the 2014 event dwarfed the 1991/92 and 1994/95 events. Figure 8
If we focus on the tropical Pacific, then the El Niño processes in 2014 resulted in a relatively strong event…definitely much stronger than what is reflected in the surface temperatures of the NINO3.4 region. The natural warming of the tropical Pacific in response to the two downwelling (warm) Kelvin waves last year helped to make 2014 the (possible) warmest year on record for the GISS, UKMO and old NOAA global land+ocean surface temperature datasets. But as discussed in the post Did ENSO and the “Monster” Kelvin Wave Contribute to the Record High Global Sea Surface Temperatures in 2014?, The Blob in the eastern extratropical North Pacific was the primary cause of the uptick in surface temperatures last year.
NOTE: The unrealistic recent warming in the new global land+ocean surface temperature data from NOAA, on the other hand, is of course dependent on NOAA’s excessive and unjustifiable bias adjustments to their sea surface temperature during the hiatus. See the Open Letter to Tom Karl of NOAA/NCEI Regarding “Hiatus Busting” Paper.
The Reynolds OI.v2 sea surface temperature data are available from the KNMI Climate Explorer.