This post provides an update on the progress of the early evolution of the 2014/15 El Niño with data through the beginning of July 2014. The post is similar in layout to the May and June updates. The post includes 3 gif animations and 13 illustrations so the post might take a few moments to load on your browser. Please click on the illustrations and animations to enlarge them.
Included are updates of the weekly sea surface temperature anomalies for the four most-often-used NINO regions. Also included are updates of the GODAS map-based animations of sea surface height anomalies, T300 anomalies (depth-averaged temperature anomalies to 300 meters), sea surface temperature anomalies, and the cross sections of temperature anomalies at depth along the equator. These animations start in January 2014 for the full progress of this year’s event. Also included are a couple of graphs of the BOM Southern-Oscillation Index (SOI) and the NOAA Equatorial SOI.
We compared the evolution of the 2014/15 El Niño to the 1982/83 and 1997/98 El Niños in a number of posts in this series, back when it was thought this El Niño was going to be a strong event. We don’t see those comparisons as often, but people may still expect to see the comparisons in my posts, so I’ve updated those graphs. And since we’ve been watching the downwelling (warm) Kelvin wave as it makes its way east along the equator in the Pacific, 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, as we did with the May and June updates, we’ll take a look at a number of Hovmoller diagrams comparing the progress so far this year to what happened in 1997. All will serve as a background for a general discussion of what we’re still waiting to happen if this El Niño is to continue to evolve.
NINO REGION TIME-SERIES GRAPHS
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)
As of last week, the sea surface temperature anomalies in all four equatorial NINO regions remained elevated—a result of the warmer-than-normal subsurface waters (associated with the Kelvin wave) being drawn to the surface. Note how all but the NINO3 region sea surface temperatures appear to have peaked already. As we’ll see, that is not unusual.
EL NIÑO EVOLUTION COMPARISONS FOR NINO REGION SEA SURFACE TEMPERATURE ANOMALIES
Using weekly sea surface temperature anomalies for the four NINO regions, Figure 2 updates the comparisons of the evolutions of this El Niño with the 1982/83 and 1997/98 events. As you’ll recall, the NINO3.4 and NINO1+2 comparisons were originally provided in the post 2014/15 El Niño – Part 3 – Early Evolution – Comparison with 1982/83 & 1997/98 El Niño Events. This year, NINO3.4 region sea surface temperature anomalies, the primary ENSO index, are well behind the two earlier strong El Niños. The NINO4 region temperature anomalies are dropping. NINO3 region temperature anomalies have flattened in recent weeks. And in the NINO1+2 region, the temperature anomalies appear as though they may have started to decline from a peak a few weeks ago. The NINO1+2 data are an indicator of an East Pacific El Niño, which are stronger than Central Pacific El Niños.
In the first post in this series, we discussed a number of animations of maps and animations of equatorial cross sections available from the NOAA Global Ocean Data Assimilation System (GODAS) website. Each cell of the animation is a 5-day (pentadal) average. Those animations ran from January 3rd to March 29th. The following are updates, again starting in January 3rd. GODAS only maintains their animations for 3 months. I’ve stored the maps since the first of the year and will continue to add maps as time progresses. That way we can watch the El Niño unfold from the beginning and then try to keep track of the warm water when El Niño is over.
Animation 1 provides the sea surface height anomalies and the depth-averaged temperature anomalies for the top 300 meters (T300) side by side.
Animation 2 is a similar side-by-side comparison, but on the left are maps of sea surface temperature anomalies and on the right are the H300 maps. The sea surface temperature maps trail the others by a pentad or two, which is why they do not run through July 2. (My apologies for the shift in the color scaling for the range of +0.5 to +1.0 deg C in the sea surface temperature anomaly maps. That appears to be a quirk of my computer, not the GODAS website.)
Animation 3 is an update of the cross sections of temperature anomalies at depth along the equator.
EL NIÑO EVOLUTION COMPARISONS WITH TAO PROJECT SUBSURFACE DATA
The NOAA Tropical Atmosphere-Ocean (TAO) Project website includes data for two temperature-related datasets for 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)
- 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.
In the following three graphs, we’re comparing data for the evolution of the 2014/15 El Niño so far (through the end of May 2014) with the data for the evolutions of the 1982/83 and 1997/98 El Niños. The Warm Water Volume data are the top graphs and the depth-averaged temperature data are the bottom graphs. As you’ll see, the curves of two datasets are similar.
Let’s start with the Western Equatorial Pacific (5S-5N, 120E-155W), Figure 3. The warm water volume and depth-averaged temperature data show the Western Equatorial Pacific had slightly less warm water or was slightly cooler this year than during the opening months of 1997. But 2014 had more warm water or was warmer than 1982.
In the second post in this series, we showed that the ocean heat content for the entire eastern tropical Pacific (24S-24N, 180-80W), for the depths of 0-700 meters, was cooler before the start of the current El Niño than it was in before the start of 1997 El Niño. (See the graph here.) The warm water volume and depth-averaged temperature data shown in Figure 4 for the eastern equatorial Pacific also show lower warm water volume and lower depth-averaged temperatures in 2014 than in 1997.
As a result, across the entire equatorial Pacific, Figure 5, warm water volume is lower and depth-averaged temperatures are less in 2014 than they were in 1997. Then again, they’re higher than they were in 1982.
Keep in mind, though, that both the 1982/83 and 1997/98 events were strong El Niños.
It will be interesting to see how far the NODC ocean heat content data for the tropical Pacific dropped as a result of this El Niño. We’ll have to wait for their April-June 2014 update, which should be available in a few months.
SOUTHERN OSCILLATION INDEX (SOI)
The Southern Oscillation Index 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 this series. It is derived from the sea level pressures of Tahiti and Darwin, Australia. 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 June 2014 Southern Oscillation Index value is -1.5, which is still within ENSO-neutral conditions. The BOM threshold for El Niño conditions is an SOI value of -8.0, so there’s a long way to go. Figure 6 presents a time-series graph of the SOI data.
Figure 7 compares the evolution of the SOI values this year to those in 1982 and 1997, the development years of the strong 1982/83 and 1997/98 El Niños. The Southern Oscillation Index this year is lagging well behind the values in 1982 and 1997.
For those of you interested in keeping a closer eye on the BOM Southern Oscillation Index, see the BOM Recent (preliminary) Southern Oscillation Index (SOI) values webpage. For the past 6 days, the 30-day running-average of the SOI has been hovering in the -4.0 to -5.0 range, suggesting that the trade winds might be working their way toward El Niño conditions. Then again, the sea level pressures of Tahiti and Darwin, Australia are often impacted by off-equatorial weather events that do not always reflect what’s happening along the equator in the Pacific.
In Part 8 of this series, we also presented NOAA’s Equatorial Southern Oscillation Index. Where the original Southern Oscillation Index is based on sea level pressures in Tahiti and Darwin, Australia, the NOAA Equatorial Southern Oscillation Index, as its name suggests, is based on the sea level pressures of the eastern and western equatorial Pacific. The time-series graph through June 2014 is shown in Figure 8, and the evolution this year is compared to the 1982/83 and 1997/98 El Niños in Figure 9. The NOAA Equatorial Southern Oscillation Index was still positive in June, which is a further indication that the trade winds are not cooperating with the development of the El Niño this year.
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COMPARISONS OF HOVMOLLER DIAGRAMS OF THIS YEAR (TO DATE) WITH 1997
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) with 2014 on the left and 1997 on the right. GODAS, unfortunately, furnishes the illustrations (not the data) in different dimensions for the two years. The vertical (y) axis in both is time with the Januarys for both years at the top and Decembers at the bottom. The horizontal (x) axis is longitude, so, moving from left to right, 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 along a band from 2S to 2N. The positive anomalies, working their way eastward since the beginning of 2014, were caused by the downwelling Kelvin wave, which pushes 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. The 1997/98 El Niño was preceded by two downwelling Kelvin waves shown in the right-hand Hovmoller in Figure 10. The first one that began in 1996 wasn’t very strong, but the second one that began a few months later in 1997 was enough to start the 1997/98 El Niño.
Note how the thermocline continued to drop in the eastern equatorial Pacific as 1997 progressed. The 1997/98 El Niño was a freak. So much warm water flooded from the western tropical Pacific into the eastern portion that the normal warm water distribution below the surface of the equator reversed. That is, normally there is more warm water in the western portion than in the eastern portion of the equatorial Pacific so that the thermocline slopes upward from west to east, but at the peak of the 1997/98 El Niño, there was more warm water in the central and eastern portion than the west, with the slope of the thermocline growing downward from west to east. (See the cross section from ECMWF here.)
Figure 11 presents the 2014-to-date and 1997 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.
The two westerly wind bursts shown in red in the western equatorial Pacific in 2014 are associated with the downwelling Kelvin wave, and the westerly bursts early in 1997 are associated with the Kelvin waves that year. (See the post ENSO Basics: Westerly Wind Bursts Initiate an El Niño.) Note how in 1997, as the May progressed through September, the negative wind stresses decreased (associated with a weakening of the trade winds), with the neutral whites expanding eastward. Also note the repeated westerly wind bursts in the western equatorial Pacific from August through November. Those westerly wind bursts throughout 1997 continued to help push warm water from the western equatorial Pacific into the east, strengthening the 1997/98 El Niño.
Figure 12 presents the Hovmollers of wind stress anomalies…just a different perspective. Note how there were more positive wind stress anomalies in the western equatorial Pacific in 1997 than there have been so far this year.
And Figure 13 presents the Hovmollers of sea surface temperature anomalies. Unfortunately, the Hovmoller of sea surface temperature anomalies is delayed a few weeks…thus the purplish line. But as we’ve seen in the comparison graphs in Figure 2, the sea surface temperature anomalies of the NINO3.4 and NINO3 regions in 2014 are starting to fall behind those of 1997, and the sea surface temperature anomalies this year in the NINO1+2 region are less than they were at this time in 1997. As you’ll note in the Hovmoller for this year, it didn’t take long for the La Niña conditions in the eastern equatorial Pacific to disappear. Will the present El Niño conditions disappear as quickly?
THE EL NIÑO WILL DIE WITHOUT THE ATMOSPHERIC FEEDBACKS
The El Niño- and La Niña-related acronym ENSO stands for El Niño-Southern Oscillation. El Niño, to the left of the hyphen, represents the ocean portion, while Southern Oscillation, to the right of the hyphen, represents the atmospheric component. In other words, ENSO involves a coupling of ocean and atmospheric processes. For an El Niño to form, the ocean or atmospheric portions must both cooperate.
We saw a strong downwelling Kelvin wave this year, which gave ENSO researchers and global warming enthusiasts hope for a strong El Nino. See Figure 10. It wasn’t quite as strong as the 1997/98 El Niño but the Kelvin wave was strong enough to draw comparisons.
But, referring back to Figure 11, we’re definitely not seeing a comparative weakening of the trade winds this year, and there have been fewer westerly wind bursts than there were in 1997. The additional westerly wind bursts and the continued weakening of the trade winds are what drive additional warm water from the western tropical Pacific into the eastern equatorial Pacific, thus reinforcing the development of the El Niño. Those are the additional feedbacks that are absent so far this year.
We monitor the Southern Oscillation Index, which is a metric based on the difference in sea level pressures in the eastern and western tropical Pacific. Because the trade winds and the sea level pressure difference between those two points are interrelated, the Southern Oscillation Index, in turn, reflects the strength and direction of the trade winds. The dip of the BOM Southern Oscillation Index into negative values indicates the trade winds have weakened over the past few months, but the trade winds have not weakened to the values that are associated with strong El Niños.
The El Niño conditions in the sea surface temperatures of the equatorial Pacific (Figures 1 and 2) are the result of the additional subsurface warm water that had been carried east by the downwelling Kelvin wave. But as we can see in the animations, the supply of warmer-than-normal subsurface water is quickly being used up as it is drawn to the surface. If the trade winds don’t start to weaken and if we don’t see additional westerly wind bursts, the 2014 El Niño will die.
In the June 2014 sea surface temperature update, I showed that global sea surface temperatures were at record high levels this year. I also noted the reasons. So you can expect to see GISS, NOAA and UKMO proclaiming more record-high global surface temperatures in upcoming 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?
And 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
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.
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. (I also am very happy to receive tips or donations.)