Guest Post by Bob Tisdale
This post provides an update of many of the ENSO-related variables we presented as part of last year’s 2014-15 El Niño Series. For the series about the 2015/16 El Niño, we’ve used the evolution years of different El Niños as references to the goings-on in 2015. This month we’re including the 1997/98 El Niño because it was the strongest El Niño in our short instrument temperature record. For the other reference, we’re using 1982, which was the second strongest El Niño.
There are a number of notable things this month. First, sea surface temperature-based indices and the Southern Oscillation Index indicate the El Niño has peaked. And we discussed in the December update the upwelling Kelvin wave that will be effecting (decreasing) El Niño conditions. Those indicators do not mean the El Niño will immediately stop impacting weather conditions around the globe. Strong El Niño conditions still exist in the tropical Pacific, and there is still a large volume of El Niño-related warmer-than-normal waters below the central and eastern equatorial Pacific (see animation from GODAS website here). Strong El Niño conditions are likely to exist through February to April and weak El Niño conditions might last until June. See Figure Supplement-1. Expect unusual El Niño-caused weather anomalies for many months to come…some bad, some good.
Second, there are many persons and government agencies around the globe claiming that precipitation-based weather events are worse than ever during this El Niño due to human-induced global warming. One wonders how they can make that claim when the consensus (the average) of the climate models used by the IPCC for their 5th Assessment Report shows no long-term increase in global precipitation from 1861 (the start year of the mean of the climate model outputs) to 1999 (the end of the 20th Century)…just some volcano-related dips and rebounds. See Figure Supplement 2, which is Figure Intro-15 from my recently published (free) ebook On Global Warming and the Illusion of Control – Part 1 (25MB). That illustration is discussed further on page 29 (pdf page 30) of the ebook.
Figure Supplement 2
That is, data indicate Earth’s surfaces have warmed from 1861-1999, but the climate models used by the IPCC show no long-term increase in precipitation in that time. Alarmists defy common sense when they claim precipitation around the globe is increasing in response to global warming, when the climate models used by the IPCC show no increase from 1861 to 1999. Then again, I don’t believe anyone has ever claimed that alarmists display common sense.
Third, as discussed last month, NOAA uses the sea surface temperature anomalies of the NINO3.4 region as their primary metric for determining the strength of an El Niño. Based on the weekly and monthly Reynolds OI.v2 data, NINO3.4 region sea surface temperature anomalies had been running slightly ahead of the 1997/98 El Niño. Of course, alarmists have been proclaiming “worst ever” and other such nonsense. However, as we discussed in the post Is the Current El Niño Stronger Than the One in 1997/98?, the 1997/98 El Niño was a stronger East Pacific El Niño than the one taking place now. Also see the post The Differences between Sea Surface Temperature Datasets Prevent Us from Knowing Which El Niño Was Strongest According NINO3.4 Region Temperature Data, because the results vary depending on the sea surface temperature dataset. I’ve updated the comparison graph with the different sea surface temperature datasets (end products) in Figure Supplement 1 above.
And if you still want to argue that the El Niño this year is stronger than the 1997/98 event, see the post Exactly the same, but completely different: why we have so many different ways of looking at sea surface temperature at the NOAA ENSO Blog.
Fourth, there are new looks for many of the graphs and Hovmoller diagrams. For the transition to La Niña (assuming one will form in 2016), I’ve extended the x-axis (horizontal axis) of the evolution graphs to include 24 months of data (100 weeks for the weekly data). I’ve also spliced on the transition years from El Niño to La Niña (1983, 1998 and 2016) onto the Hovmoller diagrams that have been presented in this series.
Fifth, the Southern Oscillation Index for December 2015 has returned to El Niño conditions after a drop into ENSO neutral conditions in November.
Sixth, I have not included maps or equatorial subsurface temperature anomalies from the GODAS website in this update. Scroll down to the bottom of the linked webpage for the most recent illustrations and animations.
ENSO METRIC UPDATES
This post provides an update on the progress of the evolution of the 2015/16 El Niño with monthly data through the end of December 2015, and for the weekly data through early-January, 2016. The post is similar in layout to the updates that were part of the 2014/15 El Niño series of posts here. (The series of posts about the 2015/16 El Niño is here.) The remainder of the post includes 17 illustrations so it might take a few moments to load on your browser. Please click on the illustrations to enlarge them.
Included are updates of the weekly (and monthly) sea surface temperature anomalies for the four most-often-used NINO regions. Also included are a couple of graphs of the monthly BOM Southern-Oscillation Index (SOI) and the NOAA Multivariate ENSO Index (MEI).
For the comparison graphs we’re using the El Niño events of 1997/98 and 1982/83 (the two strongest El Niño events during recent decades) as references for 2015/16.
Also included in this post are evolution comparisons using warm water volume anomalies and depth-averaged temperature anomalies from the NOAA TOA project website.
Then, we’ll take a look at a number of Hovmoller diagrams comparing the progress so far for the 2015/16 El Niño to the El Niños of 1982/83 and 1997/98.
NINO REGION TIME-SERIES GRAPHS
Note: The weekly NINO region sea surface temperature anomaly data for Figure 1 are from the NOAA/CPC Monthly Atmospheric & SST Indices webpage, specifically the data here. The anomalies for the NOAA/CPC data are referenced to the base years of 1981-2010.
Figure 1 includes the weekly sea surface temperature anomalies of the 4 most-often-used NINO regions of the equatorial Pacific. From west to east they include:
- NINO4 (5S-5N, 160E-150W)
- NINO3.4 (5S-5N, 170W-120W)
- NINO3 (5S-5N, 150W-90W)
- NINO1+2 (10S-0, 90W-80W)
Note that the horizontal red lines in the graphs are the present readings, not the trends.
EL NIÑO EVOLUTION COMPARISONS FOR NINO REGION SEA SURFACE TEMPERATURE ANOMALIES
Using weekly sea surface temperature anomalies for the four NINO regions, Figure 2 compares the goings on this year with the 1997/98 event. While sea surface temperature anomalies in the NINO4 and NINO3.4 regions peaked higher than in 1997, the NINO1+2 and NINO3 regions lagged well behind the 1997/98 El Niño. In other words, the 1997/98 El Niño was a stronger East Pacific El Niño than the 2015/16 El Niño.
Note how the NINO3.4 sea surface temperature anomalies are showing a decline over the past 7 weeks. The weekly data are impacted by “weather noise” so we could see another uptick, but I suspect we’ve reached the peak of this El Niño. El Niños are tied to the seasonal cycle and typically peak in November to January. See the post here.
The weekly Reynolds OI.v2-based NINO-region data start in 1990 at the NOAA/CPC Monthly Atmospheric & SST Indices webpage. Thus the absence of the 1982/83 event in Figure 2.
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 plethora of atmospheric variables…thus “multivariate”.
According to the most recent Multivariate ENSO Index update discussion, strong El Niño conditions exist, but they are lagging behind the events of 1982/83 and 1997/98:
Compared to last month, the updated (November-December) MEI has dropped slightly (by 0.19) to +2.12, continuing at the 3rd highest ranking, and about 0.3 sigma behind 1982 and 1997 for this season. The August-September 2015 value of +2.53 remains the third highest overall at any time of year since 1950. The evolution of the 2015 El Niño remains very similar to 1997, as monitored by the MEI, including a first peak in August-September and subsequent weakening during the remainder of the calendar year. In 1998, this was followed by a fairly strong rebound that peaked in late boreal winter 0.4 sigma higher than in Novemeber-December.
There’s something else to consider about the MEI. 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.
The Multivariate ENSO Index update discussion and data for November/December were posted on January 5th. Figure 3 presents a graph of the MEI time series starting in Dec/Jan 1979. And Figure 4 compares the evolution this year to the reference El Niño-formation years of 1982 and 1997.
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Obviously, according to the NOAA Multivariate ENSO Index (MEI), the 1997/98 event was stronger than the one in 2015/16.
EL NIÑO EVOLUTION COMPARISONS WITH TAO PROJECT SUBSURFACE DATA
IMPORTANT NOTE: The 1982 values of the TAO Project subsurface data have to be taken with a grain of salt. The deployment of the TOA project buoys started in the late 1980s and was not compete until the early 1990s. Also keep in mind that these values are the output of a reanalysis, not observations-only-based data.
The NOAA Tropical Atmosphere-Ocean (TAO) Project website includes the outputs of a reanalysis for two temperature-related datasets for the waters below the equatorial Pacific. See their Upper Ocean Heat Content and ENSO webpage for descriptions of the datasets. The two datasets are Warm Water Volume (above the 20 deg C isotherm) and the Depth-Averaged Temperatures for the top 300 meters (aka T300). Both are available for the:
- Western Equatorial Pacific (5S-5N, 120E-155W)
- Eastern Equatorial Pacific (5S-5N, 155W-80W)
- Total Equatorial Pacific (5S-5N, 120E-80W)
Keep in mind that the longitudes of 120E-80W stretch 160 deg, almost halfway around the globe. For a reminder of width of the equatorial Pacific, see the protractor-based illustration here. Notice also that the eastern and western data are divided at 155W, which means the “western” data extend quite a ways past the dateline into the eastern equatorial Pacific.
In the following three illustrations, we’re comparing reanalysis outputs for the evolution of the 2015/16 El Niño so far (through month-to-date December 2015) with the outputs for the evolutions of the 1982/83 and 1997/98 El Niños. The Warm Water Volume outputs are the top graphs and the depth-averaged temperature outputs are the bottom graphs. As you’ll see, the curves of two datasets are similar, but not necessarily the same.
Let’s start with the Western Equatorial Pacific (5S-5N, 120E-155W), Figure 5. The warm water volume and depth-averaged temperature anomalies show the Western Equatorial Pacific began 2015 with noticeably less warm water than during the opening months of 1997. The warm water volume in 1982 was comparable at the start of this year but depth-averaged temperature anomalies started off higher in 2015 than in 1982. Both western equatorial datasets now, though, are higher than in both 1982 and 1997.
Both warm water volume and depth-averaged temperature anomalies in the Eastern equatorial Pacific (5S-5N, 155W-80W) in 2015 never reached values seen 1997, but have been greater than the 1982 values for most of the year. See Figure 6.
The total of the TAO project eastern and western equatorial subsurface temperature-related reanalysis outputs, Figure 7, are as one would expect looking at the subsets.
SOUTHERN OSCILLATION INDEX (SOI)
The Southern Oscillation Index (SOI) from Australia’s Bureau of Meteorology is another widely used reference for the strength, frequency and duration of El Niño and La Niña events. We discussed the Southern Oscillation Index in Part 8 of the 2014/15 El Niño series. It is derived from the sea level pressures of Tahiti and Darwin, Australia, and as such it reflects the wind patterns off the equator in the southern tropical Pacific. With the Southern Oscillation Index, El Niño events are strong negative values and La Niñas are strong positive values, which is the reverse of what we see with sea surface temperatures. The December 2015 Southern Oscillation Index value is -9.1, which is a greater negative value than the threshold of El Niño conditions. (The BOM threshold for El Niño conditions is an SOI value of -8.0.) Figure 8 presents a time-series graph of the SOI data. Note that the horizontal red line is the present monthly value, not a trend line.
The graphs in Figure 9 compare the evolution of the SOI values this year to those in 1982 and 1997…the development years of the 1982/83 El Niño and the 1997/98 El Niño. The top graph shows the raw data. Because the SOI data are so volatile, I’ve smoothed them with 3-month filters in the bottom graph. Referring to the smoothed data, the Southern Oscillation Index has recently surpassed the values in 1997 but is still lagging behind the values in 1982.
Also see the BOM Recent (preliminary) Southern Oscillation Index (SOI) values webpage. The current 30-day running average and the 90-day average is still in El Niño conditions. Note, however, in the daily data, the recent return of strong El Niño values (high negative numbers) during the past two weeks or so.
COMPARISONS OF HOVMOLLER DIAGRAMS OF THIS EL NIÑO (TO DATE) WITH 1982/83 AND 1997/98 EVENTS
NOTE: The NOAA GODAS website has not yet added 2015 to their drop-down menu for Hovmoller diagrams. For the following illustrations, I’ve used the Hovmoller diagrams available for the past 12 months, deleted the 2014 data and aligned the 2015 data with the other 2 years.
Also note that I’ve extended the Hovmoller diagrams by splicing the second years onto the first years so that we can compare the evolutions and decays of the El Niños and the transitions to La Niña, assuming a La Niña forms in 2016.
Hovmoller diagrams are a great way to display data. If they’re new to you, there’s no reason to be intimidated by them. Let’s take a look at Figure 10. It presents the Hovmoller diagrams of thermocline depth anomalies (the depth of the isotherm at 20 deg C. Water warmer than 20 deg C is above the 20 deg C isotherm and below it the water is cooler). 2015 is in the center, 1997 on the left and 1982 to the right. (Sorry about the different sizes of the Hovmollers, but somewhere along the line NOAA GODAS changed them, but they are scaled, color-coded, the same.)
The vertical (y) axis in all the Hovmollers shown in this post is time with the Januarys at the tops and Decembers at the bottoms. The red horizontal lines separate the evolution years from the decay (transition) years. The horizontal (x) axis is longitude, so, moving from left to right in each of the three Hovmoller diagrams, we’re going from west to east…with the Indian Ocean in the left-hand portion, the Pacific in the center and the Atlantic in the right-hand portion. We’re interested in the Pacific. The data are color-coded according to the scales below the Hovmollers.
Figure 10 is presenting the depth of the 20 deg C isotherm (which separates the warmer water above from the cooler water below) along a band from 2S to 2N. The positive anomalies, working their way eastward early in 1982, 1997 and 2015, were caused by downwelling Kelvin waves, which push down on the thermocline (the 20 deg C isotherm). You’ll note how the anomalies grew in strength as the Kelvin wave migrated east. That does not mean the Kelvin wave is getting stronger as it traveled east; that simply indicates that the thermocline is normally closer to the surface in the eastern equatorial Pacific than it is in the western portion. In this illustration, we’re looking at anomalies, not absolute values.
Based on thermocline depth anomalies, the El Niño conditions were much stronger in 1997 than they were in 1982 and in 2015.
Figure 11 presents the Hovmollers for wind stress (not anomalies) along the equator. The simplest way to explain them is that they’re presenting the impacts of the strengths and directions of the trade winds on the surfaces of the equatorial oceans. In this presentation, the effects of the east to west trade winds at various strengths are shown in blues, and the reversals of the trade winds into westerlies are shown in yellows, oranges and reds. To explain the color coding, the trade winds normally blow from east to west; thus the cooler colors for stronger east to west trade winds. The reversals of the trade winds (the yellows, oranges and reds) are the unusual events and they’re associated with El Niños, which are the abnormal state of the tropical Pacific. (A La Niña is simply an exaggerated normal state.)
The two westerly wind bursts shown in red in the western equatorial Pacific in 1997 are associated with the strong downwelling Kelvin wave that formed at the time. (See the post ENSO Basics: Westerly Wind Bursts Initiate an El Niño.) Same thing with the three westerly wind bursts early in 2015, January through March: they initiated the Kelvin wave this year. Throughout 1997, there was a series of westerly wind bursts in the western equatorial Pacific. Same thing occurred in 2015. There were comparatively few westerly wind bursts early in 1982 and they appear early that year to have been weaker than those in 1997 and 2015, according to this GODAS reanalysis. But there was a strong westerly wind burst later in 1982. Returning to this year, the most recent westerly wind burst happened in late December 2015/early January 2016.
Figure 12 presents the Hovmollers of wind stress anomalies…just a different perspective. But positive wind stress anomalies, at the low end of the color-coded scale, are actually a weakening of the trade winds, not necessarily a reversal.
NOTE: There are a number of wind stress-related images on meteorological websites. Always check to see if they’re presenting absolute values or anomalies.
And Figure 13 presents the Hovmollers of sea surface temperature anomalies along the equator.
Notice how warm the eastern equatorial Pacific got during the evolution of the 1997/98 El Niño. While the sea surface temperatures this year have reached well above threshold of a strong El Niño, they’ve still well behind those of the 1997/98 El Niño…especially east of 120W (to about 90W), where sea surface temperature anomalies were more than 4.0 deg C at this time. In 1982, sea surface temperature anomalies also reached 4.0 deg C, but we did not see those values in 2015.
That is, as noted earlier, the 1997/98 was a stronger East Pacific El Niño than the one taking place in 2015.
ANIMATIONS OF GODAS MAPS AND CROSS SECTIONS – JANUARY 2015 TO PRESENT
I have not included maps or cross sections from the GODAS website in this post. Again, scroll down to the bottom of the linked webpage for the most recent illustrations and animations.
EL NIÑO REFERENCE POSTS
For additional introductory discussions of El Niño processes see:
- An Illustrated Introduction to the Basic Processes that Drive El Niño and La Niña Events
- El Niño and La Niña Basics: Introduction to the Pacific Trade Winds
- La Niñas Do NOT Suck Heat from the Atmosphere
- ENSO Basics: Westerly Wind Bursts Initiate an El Niño
Also see the entire 2014-15 El Niño series. We discussed a wide-range of topics in those posts.
WANT TO LEARN MORE ABOUT EL NIÑO EVENTS AND THEIR AFTEREFFECTS?
My ebook Who Turned on the Heat? goes into a tremendous amount of detail to explain El Niño and La Niña processes and the long-term aftereffects of strong El Niño events. Who Turned on the Heat? weighs in at a whopping 550+ pages, about 110,000+ words. It contains somewhere in the neighborhood of 380 color illustrations. In pdf form, it’s about 23MB. It includes links to more than a dozen animations, which allow the reader to view ENSO processes and the interactions between variables.
Last year, I lowered the price of Who Turned on the Heat? from U.S.$8.00 to U.S.$5.00. And the book sold well. It continues to do so this year.
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.
My sincerest thanks to everyone who has purchased a copy of Who Turned on the Heat? as a result of the El Niño posts in 2014 and from this year’s El Nino series.
A NEW BOOK AND IT’S FREE
I also published On Global Warming and the Illusion of Control (25MB .pdf) back in November. The introductory post is here. It also includes detailed discussions of El Niño events and their aftereffects…though not as detailed as in Who Turned on the Heat?