In the preceding post, we looked at the evolution of the weekly sea surface temperature anomalies in two regions of the equatorial Pacific (NINO3.4 and NINO1+2), comparing the data so far in 2014 to those of the strong 1982/83 and 1997/98 El Niño events. (See 2014/15 El Niño – Part 3 – Early Evolution – Comparison with 1982/83 & 1997/98 El Niño Events.) We presented them because there are a lot of comparisons of this El Niño to those strong El Niños.
In this post, using the same two regions, we’ll compare the evolution of the sea surface temperature anomalies this year to the rest of the satellite-era El Niño events. And we’ll also compare this year to the average, because someone was bound to ask.
This post serves solely as a reference. What it illustrates very well is that there is a tremendous amount of diversity in the evolutions of sea surface temperatures during El Niño events. A tremendous amount of diversity.
Are you ready for some spaghetti?
BEFORE WE START
The processes that initiate each El Niño are basically the same: a downwelling (warm) Kelvin wave heads east along the equator in the Pacific. We illustrated this year’s downwelling Kelvin wave in the first post in this series. The waters at the surface and below the surface of the equatorial Pacific are normally warmer in the west than in the east. So the downwelling Kelvin wave, which is carrying (basically shifting) warm water from west to east below the surface, causes the subsurface temperatures to be warmer than normal along the central and eastern portions of the equator. That warmer-than-normal subsurface water is drawn to the surface in a process called upwelling, and when it reaches the surface, the sea surface temperature anomalies begin to increase along the central and eastern portions of the equatorial Pacific. That’s where we are. The warmer-than-normal subsurface water is being drawn to the surface.
Now consider that the Kelvin waves don’t start at exactly the same time each year…and the Kelvin waves don’t have the same amount of warm water available, so they don’t all create the same subsurface temperature anomalies…and the sea surface temperatures at the start of each El Niño are somewhat different…and the strengths of the trade winds can also be different…and a multitude of other background states are all in different states. That’s why we’re going to see a lot of spaghetti when we compare the evolution of this year’s sea surface temperature anomalies with all the other satellite-era El Niños.
COMPARISONS WITH OTHER SATELLITE-ERA EL NIÑOS (NOT 1982/83 & 1997/98 EL NIÑOS)
Figures 1 and 2 illustrate the evolutions of the weekly sea surface temperature anomalies from the first week in a given year through the 60th week, so the data stretch into the first few months of the second year of each El Niño. (El Niños normally peak in boreal winter, because they are tied to the seasonal cycle.) The NOAA Oceanic NINO Index (ONI) was used as a reference for “official” El Niño events. We’re using the weekly Reynolds OI.v2 data, which starts in late 1981. In addition to where we stand so far for the 2014/15 El Niño (highlighted in red), Figures 1 and 2 also include the evolutions of the sea surface temperature anomalies for the 1986/87 El Niño, 1991/92 El Niño, 1994/95 El Niño, 2002/03 El Niño, 2004/05 El Niño, 2006/07 El Niño and the 2009/10 El Niño. Figure 1 is for the NINO3.4 region, which is located on the east-central portion of the equatorial Pacific (5S-5N, 170W-120W). Figure 2 is for the NINO1+2 region, and it is located in the eastern equatorial Pacific (10S-0, 90W-80W), just south and
west (oops) east of the Galapagos Islands.
You’ll note also that I’ve highlighted the 2006/07 El Niño. Of the group shown, it is the only east Pacific El Niño. The others are El Niño Modoki (central Pacific El Niños). See the posts There Is Nothing New About The El Nino Modoki and Comparison of El Nino Modoki Index and NINO3.4 SST Anomalies, and also see the JAMSTEC ENSO Modoki webpage (El Niño Modoki are a new category. Historically, they are not a new type of event.)
There’s so much spaghetti in the following two graphs, there’s no reason for me to describe them, other than to say there’s lots of diversity during the evolutions of El Niño events.
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Obviously, each El Niño starts from a different background, in terms of sea surface temperature anomalies. (We’ve already discussed the ocean heat content and subsurface temperature anomalies, noting that both are lower now than they were at the start of the 1997/98 El Niño. See the post here.)
COMPARISONS WITH AVERAGES OF SATELLITE-ERA EL NIÑOS (INCLUDING THE 1982/83 & 1997/98 EL NIÑOS)
Figures 3 and 4 follow the same formats. But with them, we’re comparing the evolutions of the 2014/15 El Niño (so far) to the averages of all of the satellite-era El Niño events, including the 1982/83 and 1997/98 El Niños. Now in 2014, NINO3.4 sea surface temperature anomalies are warmer than average, and NINO1+2 anomalies are cooler than average.
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Do the below-average readings in the NINO1+2 region mean that the 2014/15 El Niño will be a central Pacific El Niño and not the stronger east Pacific variety? Not necessarily. As you’ll recall from Part 3 of the series, the 2014 NINO1+2 values are similar to those at the start of the 1982/83 El Niño. See the graph here. And the 1982/83 El Niño was a strong El Niño—no doubt about that.
The weekly sea surface temperature anomaly data presented in this post is available through the NOAA NOMADS website:
EARLIER POSTS IN THIS SERIES
- The 2014/15 El Niño – Part 1 – The Initial Processes of the El Niño.
- The 2014/15 El Niño – Part 2 – The Alarmist Misinformation (BS) Begins
- The 2014/15 El Niño – Part 3 – Early Evolution – Comparison with 1982/83 & 1997/98 El Niño Events
My ebook Who Turned on the Heat? goes into much more detail to explain El Niño and La Niña processes and the long-term aftereffects of strong El Niño events. I’ve lowered the price of Who Turned on the Heat? from U.S.$8.00 to U.S.$5.00. A free preview in pdf format is here. The preview includes the Table of Contents, the Introduction, the first half of section 1 (which was provided complete in the post here), a discussion of the cover, and the Closing. Take a run through the Table of Contents. It is a very-detailed and well-illustrated book—using data from the real world, not models of a virtual world. Who Turned on the Heat? is only available in pdf format…and will only be available in that format. Click here to purchase a copy. Thanks.
The next post in the series will be about the Pacific Decadal Oscillation (PDO) and its relationship to ENSO…unless, of course, the weekly NINO3.4 sea surface temperature anomalies reach the 0.5 deg C threshold of an El Niño. I started writing the PDO post about a month ago. It’s an appropriate time to raise the topic again since the PDO is often referred to in blog posts about the upcoming El Niño.