Guest Post by Bob Tisdale
The recent post at WattsUpWithThat Yes Virginia (and everyone else) there is an El Niño coming was written by Joe Bastardi of WeatherBell Analytics. As a result of that article, Joe and I exchanged a good number of emails. Once again, Joe Bastardi was more than willing to teach from the perspective of a professional meteorologist. Joe took the time on a Sunday afternoon during (U.S.) football season to discuss El Niños and forecasting with me. Thanks, Joe.
The 2014/15 El Niño has to be one for the record books. It has probably been one of the most-observed and most-studied weak El Niño events ever. It started early in the year with a large Kelvin wave (discussed in the first post of this series). Alarmists around the globe began predicting all sorts of mayhem… to be brought on by what they assumed would be a “super” El Niño…which, in turn, they claimed was caused by, and made worse by, human-induced global warming. Contrary to all the prognostications of gloom and doom, the El Niño fizzled into weak El Niño conditions during the boreal spring and summer, destroying all of the alarmists’ hopes and making some persons look exceedingly foolish… exceedingly foolish.
But one of the “constants” throughout the year has been Joe Bastardi’s forecasts that this El Niño would not be a strong event—that the El Niño would reach only weak to moderate levels.
You may, at this time, be saying to yourself, What El Niño? The El Niño hasn’t developed yet.
It depends on how we’re defining an El Niño—which index we’re referencing. That’s the topic of this post.
Now, this discussion would not be taking place if a super El Niño had developed. But that never materialized.
You may also be thinking, If it’s not a super El Niño, why do we care?
The tropical Pacific influences weather around the globe, regardless of whether the sea surface temperatures for a specific region are above or below El Niño and La Niña thresholds. In addition to the numerous other factors that dictate your regional weather, meteorologists have to rely on many indicators from the tropical Pacific when preparing their seasonal forecasts, not just the sea surface temperatures of a specific region along the equator.
I learned a good number of things from Joe Bastardi during that email exchange, but on the topic of El Niño, one of points he stressed was, I was limiting my definition of an El Niño to the one based on the sea surface temperatures of the NINO3.4 region—the classic NOAA definition. NOAA uses the sea surface temperatures of the NINO3.4 region of the equatorial Pacific for their Oceanic NINO Index (ONI) and for their classifications of “official” El Niños and La Niñas.
NOAA defines El Niño conditions as sea surface temperature anomalies of the NINO3.4 region equal to or higher than +0.5 deg C. And as of last week, the week centered on Wednesday, October 22, sea surface temperature anomalies were once again back at the threshold of El Niño conditions. Let’s expand on that.
This year, NINO3.4 sea surface temperature anomalies barely squeaked into weak El Niño conditions during the boreal summer, then dropped back toward zero, but have returned once again to the threshold of El Niño conditions…according to the weekly data. Whether the sea surface temperatures there remain at or above that threshold long enough for NOAA to classify this year’s event as an “official” El Nino has yet to be seen. (And that was how I was limiting my view of an El Niño.)
ANOTHER OF THE CURIOSITIES THIS YEAR
Figure 1 is a map of the average sea surface temperature anomalies of the tropical Pacific for May through September 2014. Highlighted on the map are the four NINO regions. More than a decade ago the NINO3.4 region was selected for use as the primary NINO index. In the 1997 paper The Definition of El Niño, Trenberth notes:
Mean temperatures are higher in the Niño 3.4 region than in Niño 3 and its proximity to the Pacific warm pool and main centers of convection is the reason for the physical importance of Niño 3.4.
This year, from May to September, the equatorial Pacific has warmed east and west of the NINO3.4 region, as shown in Figure 1. To expand on that:
The equatorial Pacific stretches almost halfway around the globe. NINO regions occupy the central and eastern portions. And while the weekly sea surface temperatures of the NINO3.4 region have occasionally reached El Niño conditions this year (just barely), the monthly values have not. See Figure 2. But the sea surface temperature anomalies for the entire central and eastern equatorial Pacific (5S-5N, 160E-80W) have been at or above +0.5 deg C since May 2014, with most of the warming taking place in the far eastern equatorial Pacific.
For some reason, the NINO3.4 region hasn’t been cooperating, but east and west of it, the equatorial Pacific has been in El Niño conditions for a good number of months, with the sea surface temperatures in the NINO1+2 region continuing to remain elevated and with the NINO3 and NINO4 regions cycling into El Niño conditions, back out and back in. See Figure 3. In fact, the NINO3 region reached the +1.0 deg C threshold of a moderate El Niño for a couple of weeks.
NOAA focuses in the NINO3.4 region with its Oceanic NINO Index, so many people, like me, also focus on it. This year, the (weak) El Niño conditions have been taking place east and west of the NINO3.4 region. Very curious.
THE 90-DAY SOUTHERN OSCILLATION INDEX IS ALSO SHOWING WEAK EL NIÑO CONDITIONS
As of October 30, 2014, the 90-day Southern Oscillation Index (SOI) value has been within weak El Niño conditions for more than 1 week, where a negative SOI value equal to or more negative than -8.0 is considered El Niño conditions.
Let’s phrase that another way: Based on the average 90-day SOI, weak El Niño conditions have existed in the tropical Pacific for the past 3 months.
CAN’T FORGET THE MULTIVARIATE ENSO INDEX
The Multivariate ENSO Index (MEI) is another ENSO index published by NOAA. It was created and is maintained by NOAA’s Klaus Wolter. The Multivariate ENSO Index uses the sea surface temperatures of the NINO3 region of the equatorial Pacific, along with a slew of atmospheric variables…thus “multivariate”.
According to the most recent Multivariate ENSO Index update discussion (my boldface):
The long anticipated emergence of El Niño conditions in 2014 has been under way since May-June, despite the lack of signal in Niño 3.4 SST…and its sudden drop in the MEI this month.
The MEI had been showing El Niño conditions for the three bimonthly periods (May-June, June-July, and July-August) before dropping out in August-September.
…(big but), keep in mind that El Niño and La Niña rankings according to the MEI aren’t based on fixed threshold values such as +0.5 for El Niño and -0.5 for La Niña. The MEI El Niño and La Niña rankings are based on percentiles, top 30% for the weak to strong El Niños and the bottom 30% for the weak to strong La Niñas. This is difficult to track, because, when using the percentile method, the thresholds of El Niño and La Niña conditions vary from one bimonthly period to the next, and they can change from year to year.
As a clarification, looking at the numerical values of the MEI timeseries, the 19th ranked positive MEI for AugSep is 0.526 (through 2014), but for the next three bimonthly periods (through 2013) the 19th ranked positive MEI’s for SepOct is 0.638, for OctNov it’s 0.645 and for NovDec it’s 0.559. It would be interesting to know why Klaus Wolter uses percentiles instead of fixed thresholds.
I’ll have to add the MEI to my next few monthly El Niño updates.
NOAA’s primary ENSO index (NINO3.4 sea surface temperature anomalies) is not indicating that we’re in weak El Niño conditions. And, when all is said and done next year, it’s entirely possible that this year’s El Niño won’t be highlighted in red on the Oceanic NINO Index. But that does not mean weather conditions are not responding to the other factors that contribute to an El Niño, where
- other factors include those considered by the Southern Oscillation Index and Multivariate ENSO Index, and
- other factors that are impacted by the sea surface temperatures of the other NINO regions east and west of the NINO3.4 region.
It all boils down to what one uses to define an El Niño and how one uses that information when making a long-term weather forecast…which is where Joe Bastardi excels.
Just a quick animation of the last two months of subsurface temperature anomalies graphics along the equator, from the NOAA GODAS website: As noted in the last two updates (here and here), there has been a strengthening of the latest downwelling (warm) Kelvin wave. That warm water should continue to travel east and be drawn to the surface over the next few months.
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
- The 2014/15 El Niño – Part 4 – Early Evolution – Comparison with Other Satellite-Era El Niños
- The 2014/15 El Niño – Part 5 – The Relationship Between the PDO and ENSO
- The 2014/15 El Niño – Part 6 – What’s All The Hubbub About?…
- The 2014/15 El Niño – Part 7 – May 2014 Update and What Should Happen Next
- The 2014/15 El Niño – Part 8 – The Southern Oscillation Indices
- The 2014/15 El Niño – Part 9 – Kevin Trenberth is Looking Forward to Another “Big Jump”
- The 2014/15 El Niño – Part 10 – June 2014 Update – Still Waiting for the Feedbacks
- The 2014/15 El Niño – Part 11 – Is the El Niño Dying?
- The 2014/15 El Niño – Part 12 – July 2014 Update – The Feedbacks Need to Kick in Soon
- The 2014/15 El Niño – Part 13 – More Mixed Signals
- The 2014/15 El Niño – Part 14 – Warm Water Recirculated?
- The 2014/15 El Niño – Part 15 – August 2014 Update – An El Niño Mulligan?
- The 2014 15 El Niño – Part 16 – September 2014 Update – Still Seeing Mixed Signals
- The 2014/15 El Niño – Part 17 – Is There Still Hope for a Moderate El Niño?
- The 2014/15 El Niño – Part 18 – October 2014 Update – One Last Chance?
And for additional introductory discussions of El Niño processes see: