I’ve moved to WordPress. This post can now be found at More Detail On The Multiyear Aftereffects Of ENSO – Part 2 – La Nina Events Recharge The Heat Released By El Nino Events AND…
######################...During Major Traditional ENSO Events, Warm Water Is Redistributed Via Ocean Currents.
INTRODUCTION
This is Part 2 of a multipart post. It addresses critical comments about my earlier posts that dealt with the multiyear aftereffects of major traditional El Nino events. Two specific El Nino events, those in 1986/87/88 and 1997/98, caused Sea Surface Temperatures (SST) of the East Indian and West Pacific Oceans to remain at elevated levels during the subsequent La Nina events. These SST residuals, what I have called step changes in earlier posts for the sake of simplicity, bias global SST upward during the La Nina events and give the impression of a gradual increase, one that is attributed to anthropogenic greenhouse gases.
This post differs from earlier posts in that:
1. I’ve included discussions and illustrations from Pavlikus et al (2008) “ENSO Surface Shortwave Radiation Forcing over the Tropical Pacific” and presented ISCCP Cloud Amount Anomaly Maps to illustrate the locations of the cloud amount variations over the Tropical Pacific,
2. I’ve illustrated and discussed the dipole effect of El Nino events on portions of the Indian and Pacific Oceans,
3. I’ve discussed and illustrated the warm water redistribution aspect of El Nino and La Nina events, and,
4. I’ve included illustrations and quotes from Trenberth et al (2002) "Evolution of El Nino–Southern Oscillation and global atmospheric surface temperatures” to confirm my presentation and discussions of ENSO and its impacts on SST.
THE RECHARGE ASPECT OF ENSO
The processes that cause Sea Surface Temperate (SST) to rise during the discharge portion of ENSO, the El Nino, were discussed in part 1 of this post, More Detail On The Multiyear Aftereffects Of ENSO – Part 1 – El Nino Events Warm The Oceans. Trenberth et al (2002) "Evolution of El Nino–Southern Oscillation and global atmospheric surface temperatures"...
http://www.cgd.ucar.edu/cas/papers/2000JD000298.pdf
...serves as one of the references in that post. I’ll use it again here.
Trenberth et al (2002) briefly describes how La Nina events recharge the heat that had been discharged and redistributed from the tropical Pacific during El Nino events. On page 16, paragraph 57 they write, “The negative feedback between SST and surface fluxes can be interpreted as showing the importance of the discharge of heat during El Nino events and of the recharge of heat during La Nina events. Relatively clear skies in the central and eastern tropical Pacific allow solar radiation to enter the ocean, apparently offsetting the below normal SSTs, but the heat is carried away by Ekman drift, ocean currents, and adjustments through ocean Rossby and Kelvin waves, and the heat is stored in the western Pacific tropics. This is not simply a rearrangement of the ocean heat, but also a restoration of heat in the ocean.”
Note that the area referenced with “west Pacific tropics” is the Pacific Warm Pool.
In short, the La Nina restores the heat discharged and redistributed by the El Nino. This can be illustrated with a comparison graph of NINO3.4 SST anomalies and Ocean Heat Content (OHC) of the tropical Pacific, Figure 1. The discharge and recharge can be seen if you focus on the 1972/73, 1986/87/88, and 1997/98 El Nino events. Those three major El Nino events also are not impacted to any significant extent by volcanic aerosols.
http://i36.tinypic.com/eqwdvl.pngFigure 1
The recharge is accomplished by changes in cloud amount. The “relatively clear skies” in the above quote from Trenberth et al refers to the decrease in cloud amount during the La Nina phase of ENSO. The coincidence between NINO3.4 SST anomalies and Tropical Pacific Cloud Amount can be seen in a comparison graph, Figure 2.
http://i35.tinypic.com/4rxele.jpgFigure 2
And to quote Trenberth again, “Relatively clear skies in the central and eastern tropical Pacific allow solar radiation to enter the ocean, apparently offsetting the below normal SSTs…” So it’s an increase in Downward Shortwave Radiation (due to the decrease in cloud amount) that recharges the tropical Pacific OHC.
Trenberth et al did not quantify the amount of heat restored during the La Nina phase, but if you’d like an order of magnitude for the amount of heat discharged, redistributed, and recharged during major El Nino and La Nina events, you could look at the comparison graph of NINO3.4 SST anomalies and Tropical Pacific OHC, Figure 1, and again key off the 1972/73, 1986/87/88 and 1997/98 El Nino events.
CLOUD AMOUNT ASPECT OF ENSO RECHARGE PHASE IS DISCUSSED IN PAVLAKIS ET AL (2008)
In “ENSO Surface Shortwave Radiation Forcing over the Tropical Pacific” (2008), Pavlakis et al illustrated the inverse relationship between NINO3.4 SST anomalies and Downward Shortwave Radiation (visible light) anomaly (DSR-A) at the surface of the Central and Eastern Tropical Pacific:
http://www.atmos-chem-phys-discuss.net/8/6697/2008/acpd-8-6697-2008-print.pdf
The Pavlakis et al Figure 6 is shown here as Figure 3. It compares NINO3.4 SST anomalies and Downward Shortware Radiation (DSR), which is visible light, for two areas of the Central and Eastern Tropical Pacific. Note how, when NINO3.4 SST anomalies are negative, indicating a La Nina, DSR anomalies are positive, indicating that more sunlight is reaching and entering the Central and Eastern Tropical Pacific Ocean, warming it. The opposite happens during an El Nino: NINO3.4 SST anomalies are positive and DSR anomalies are negative, indicating that less visible light is warming the Central and Eastern Tropical Pacific Ocean. Keep in mind, though, that during the El Nino phase, while there may be less sunlight entering the Central and Eastern Pacific Ocean, this is happening during the discharge phase of ENSO.
http://i47.tinypic.com/eqs7d3.pngFigure 3
Some might find the Pavlakis et al Figure 1 informative. It illustrates, “The distribution of downward shortwave radiation at the surface (DSR), over the tropical and subtropical Pacific for the three month period November, December, January (NDJ); (a) eleven neutral years average, (b) average for five El Nino years, (c) average for five La Nina years.” I’ve animated the individual cells of their Figure 6 in my Figure 4. (Pavlakis et al detail the source of Figure 4 (Their Figure 6) on page 4, under the heading of “Long-term surface shortwave radiation.”)
http://i48.tinypic.com/2a9cxfq.gifFigure 4
Cell a (ENSO Neutral):
http://i49.tinypic.com/27ytmc8.png
Cell b (El Nino):
http://i47.tinypic.com/vsmkd4.png
Cell c (La Nina):
http://i49.tinypic.com/1gg07s.png
ISCCP TOTAL CLOUD AMOUNT ANOMALY MAPS ALSO ILLUSTRATE THE ENSO-CAUSED VARIATIONS
ISCCP Cloud Amount data used by Pavlakis et al are available through the KNMI Climate Explorer. Figure 5 illustrates maps of the Average Total Cloud Amount Anomalies for the Tropics for the months of November to January. These months were chosen because these are typically when ENSO events peak. The maps begin with the 1996/97 season, Cell A. There were ENSO-neutral conditions in 1996/97; NOAA ONI Index data were slightly negative
(-0.3 to -0.4 deg C). Cell A captures the negative cloud amount anomalies over the central tropical Pacific a year before the peak of the 1997/98 El Nino. Recall that the negative Total Cloud Amount anomalies indicate that DSR is positive. Then, during the peak months of the 1997/98 El Nino, Cell B, the Total Cloud Amount Anomalies are elevated over the central tropical Pacific, indicating that the convection and cloud cover has followed the warm water eastward during the El Nino. At this point, the central and eastern tropical Pacific are releasing large amounts of heat to the atmosphere. Note also that the Total Cloud Amount anomalies have dropped significantly over the western tropical Pacific and the eastern tropical Indian Ocean. This indicates that the Pacific Warm Pool is being recharged by DSR during the El Nino. Cell C shows the Total Cloud Amount Anomalies during the initial peak of the 1998/99/00/01 La Nina. Cloud Amount Anomalies are negative over the central and eastern Tropical Pacific, indicating the recharge of the heat released and redistributed during the El Nino. This pattern continues during the peak seasons of 1999/00 and 2000/01, Cells D and E. Cell F illustrates the Cloud Amount Anomalies of the ENSO-neutral 2001/02 season.
http://i46.tinypic.com/t6ccpe.pngFigure 5
IS THERE EVIDENCE OF AN IMPACT OF ANTHROPOGENIC GREENHOUSE GASES ON THE RECHARGE MODE OF ENSO?
The next logical point to address would be how much of the ocean heat recharge could be attributed to the constantly increasing infrared radiation from Anthropogenic Greenhouse Gases and how much could be attributed to the rise in visible light from the decrease in cloud amount during La Nina events. This raises the debate about the impacts of infrared radiation and visible light on Ocean Heat Content. Downward Shortwave Radiation (DSR), which is visible light, penetrates and warms the ocean for 100+ meters, while infrared radiation or Downward Longwave Radiation (DLR) only penetrates the top few centimeters. So the order of magnitude of the temporary increase in DSR (visible light) is many times greater than the long-term increase in DLR (infrared radiation) from greenhouse gases. But the argument has been presented that DLR (infrared radiation), through mixing caused by waves and wind stress turbulence, would warm the mixed layer of the ocean. This in turn would impact the temperature gradient between the mixed layer and skin, dampening the outward flow of heat from the ocean to the atmosphere. The end result according to the argument: OHC would rise due to an increase in DLR (infrared radiation) caused by increases in greenhouse gas emissions.
However, refer to the Tropical Pacific OHC data, Figure 1, again. While there is no doubt that there is a positive trend in the Tropical Pacific OHC data, the graph shows decadal and multidecadal periods of decreasing OHC. During these periods, the heat released and redistributed by the El Nino events is not replaced fully by the La Nina events. If it was, OHC trends would be flat, instead of declining. What the graph does NOT show is a gradual rise in Tropical Pacific OHC as one would expect if greenhouse gases had an influence. Also note that the heat lost during these long-term decreases is replaced and additional heat is added during two multiyear periods. Those two periods coincide with the multiyear La Nina events of 1973/74/75/76 and 1998/99/00/01. In other words, these two multiyear La Nina events add more heat than is necessary to replace the heat lost over the decadal and multidecadal periods. Without those two multiyear La Nina events, the long-term trend in Tropical Pacific OHC would be negative.
Describing the OHC anomalies in Figure 1 in more detail, for the decade from 1963 to 1973, OHC anomalies dropped gradually from ~0.04 GJ/m^2 to ~-0.3 GJ/m^2, and for the two decades from 1977 to 1997 (1999), OHC anomalies dropped gradually from ~0.16 GJ/m^2 to ~-0.12 GJ/m^2 (~-0.16 GJ.m^2). During the multiyear (4-year) period between them, from 1973 to 1977, OHC anomalies rose from ~-0.3 GJ/m^2 to ~0.16 GJ/m^2; this appears to be a recharge caused by the multiyear 1973/74/75/76 La Nina.
The curious 1995/96 upsurge in tropical Pacific OHC was explained in McPhaden (1999) “Genesis and Evolution of the 1997-98 El Nino.” It is the result of “stronger than normal trade winds associated with a weak La Nina in 1995–96.”
http://www.pmel.noaa.gov/pubs/outstand/mcph2029/text.shtml
The stronger trade winds reduce cloud amount, which, in turn, allows more DSR to warm the ocean. The stronger trade winds also feed that warm water to the Pacific Warm Pool at an elevated rate.
With that anomalous rise in Tropical Pacific OHC in 1995/96, it could be argued that the increase in tropical Pacific OHC of ~-0.08 GJ/m^2 to ~0.24 GJ/m^2 from 1998 to late 2001 was a rebound to the values established by the 1995/96 La Nina, or it could be argued that the rise in tropical Pacific OHC was caused by the multiyear 1998/99/00/01 La Nina, similar to the 1973/74/75/76 La Nina. Regardless, the data does not support the argument that Tropical Pacific OHC rises due to an increase in DLR (infrared radiation) caused by increases in greenhouse gas emissions.
THE RESPONSE OF GLOBAL TEMPERATURES TO EL NINO EVENTS ARE NOT COUNTERACTED BY LA NINA EVENTS
It is often assumed that the effects of El Nino events on global temperatures are countered by La Nina events. That is, an El Nino is known to cause an increase in global temperature, but it is assumed that a La Nina event causes a proportional decrease in global temperature. SST anomalies for many of the ocean basins, or portions thereof, do agree with the assumption. They show comparable responses to La Nina events. Refer to Figures 6 through 8. These are comparison graphs of scaled NINO3.4 SST Anomalies and the SST anomalies of the ocean basins where El Nino and La Nina events have similar effects.
http://i33.tinypic.com/w8w1hg.jpgFigure 6
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http://i35.tinypic.com/mtwh9x.jpgFigure 7
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http://i34.tinypic.com/33udefq.jpgFigure 8
However, there is a major portion of the global oceans where El Nino and La Nina events have the opposite effect on the SST anomalies. This area is well known, as is the effect. During El Nino events, Eastern Tropical Pacific SST anomalies rise, and at the same time, SST anomalies in the Western Tropical Pacific and Eastern Indian Oceans fall. During La Nina events, the opposite holds true: SST anomalies in the Eastern Tropical Pacific drop and they rise in the Western Tropical Pacific and Eastern Indian Oceans. The seesawing between the Eastern and Western Pacific SST anomalies is known as a dipole effect. This seesaw relationship can be seen in the global SST anomaly maps during El Nino and La Nina events. Refer to Figure 9, which illustrates SST anomalies near the peak of the 1997/98 El Nino and near the first seasonal peak of the 1998/99/00/01 La Nina.
http://i48.tinypic.com/xc6s0l.gifFigure 9
In fact, one phase of the opposing relationship between the SST Anomalies of the Eastern Pacific and the SST Anomalies of the Western Pacific and East Indian Oceans can be seen in the Trenberth et al sequence of lagged correlations of NINO3.4 with surface temperatures. Refer to their Figure 8, which is presented here as my Figure 10. The left-hand maps illustrate the lag correlations for the period of 1950 to 1978 and the right-hand column depicts the same for 1979 to 1998. (Trenberth et al were illustrating the differences in the evolution of El Nino events between the two periods.) I’ve highlighted the correlations at zero-month lag. The basic dipole pattern appears in both the 1950 to 1978 and 1979 to 1998 periods of the Trenberth et al Figure 8, my Figure 10. This is not an effect that is unknown.
http://i47.tinypic.com/261e1lf.pngFigure 10
Figure 11 is a comparison of East Pacific SST anomalies and the SST Anomalies of the East Indian and West Pacific Oceans. I’ve also included scaled NINO3.4 SST anomalies as a reference for timing. The 1986/87/88 and 1997/98 El Nino events and the initial portions of the subsequent La Nina events are highlighted. It is very clear that the two datasets are out of phase.
http://i49.tinypic.com/24bm92u.pngFigure 11
Figure 12 is the same comparison graph, but in it, I’ve highlighted a different portion of the data. The response of the East Pacific SST anomalies to the major El Nino events of 1986/87/88 and 1887/98 is very visible in that comparison graph. But note how little the SST anomalies of the East Indian and West Pacific drop (the area highlighted) while the SST anomalies in the East Pacific are rising dramatically. This happens because traditional El Nino events are fueled by subsurface waters from the Western Tropical Pacific, from depths to 300 meters in the Pacific Warm Pool. These subsurface waters are not included in SST measurements.
http://i47.tinypic.com/6zvkte.pngFigure 12
OCEAN CURRENTS TRANSPORT WARM WATER OUT OF THE TROPICAL PACIFIC
Figure 13 is the comparison graph of East Pacific SST anomalies and the SST Anomalies of the East Indian and West Pacific Oceans once again, but in this instance, I’ve highlighted the periods during which the SST anomalies of the East Indian and West Pacific Oceans diverge greatly from the variations in the East Pacific SST anomalies (which are correlated with NINO3.4 SST anomalies).
http://i50.tinypic.com/28ro7kk.pngFigure 13
Much of the East-West dipole effect between the East Pacific and the East Indian-West Pacific is caused by the movement of warm water within the Pacific Basin. During the formation of El Nino events, a Kelvin Wave carries warm water east. Note the eastward progression of Sea Surface Height anomalies along the equatorial Pacific illustrated in Figure 14.
http://i49.tinypic.com/21afqzd.jpgFigure 14
NOTE: The cells in Figures 14 and 15 are screen captures from the following JPL video:
http://sealevel.jpl.nasa.gov/gallery/tiffs/videos/tpglobal.mpeg
And during the La Nina, warm water is carried west by a Rossby wave that forms in the eastern Tropical Pacific north of the equator. This is illustrated in Figure 15 with the progression of Sea Surface Height anomalies from east to west.
http://i50.tinypic.com/2jewitd.jpgFigure 15
The transport of warm water from west to east during the 1997/98 El Nino formation and from east to west during the 1998/99 portion of the subsequent La Nina can also be seen quite plainly in the Sea Level Residual animation from JPL, starting at about 50 seconds into the video. (The video in mpeg format is linked above.) Let the video continue after the Kelvin and Rossby waves associated with the 1997/98 El Nino and watch how long the Sea Level Residuals in the East Indian and West Pacific Oceans remain elevated after that ENSO event.
YouTube Link:
http://www.youtube.com/watch?v=ELDkYJWHNiU
Wind-driven ocean currents also change during El Nino and La Nina phases. During the 1997/98 El Nino, the Equatorial Countercurrent in the Pacific increases in flow, Figure 16. This carries warm water from the western Tropical Pacific to the east. And during the La Nina, the flow of the Equatorial Countercurrent in the Pacific has decreased; the North and South Equatorial Currents dominate then and carry warm water back to the western Tropical Pacific.
http://i50.tinypic.com/nvqoex.pngFigure 16
After the warm water is returned to the Western Tropical Pacific, ocean currents then carry the water poleward. For those who are not familiar with Pacific Ocean currents, refer to Figure 17, which was cropped from a Wikipedia Ocean Current map here:
http://upload.wikimedia.org/wikipedia/commons/6/67/Ocean_currents_1943_%28borderless%293.png
http://i47.tinypic.com/116pd6q.pngFigure 17
Note also in Figure 17, that there is a current that flows from east to west through the Indonesian Archipelago, north of Australia, from the Tropical Pacific to the Tropical Indian Ocean. That current is called the Indonesian Throughflow. After the warm water has been returned west after the El Nino event, the Indonesian Throughflow carries it into the Tropical Indian Ocean.
Note that there are a great number of coupled ocean-atmosphere processes taking place within the Pacific Ocean before, during, and after ENSO events. The above explanation using ocean currents is very simple. Those in search of more detailed discussions could start with the references in Trenberth et al (2002).
And there will be those looking for confirmation that ocean currents redistribute warm waters that have been released by the El Nino. Trenberth et al write (page 13, paragraph 37) [My caps for emphasis], “The evolution of ENSO in the tropical Pacific Ocean illustrated here supports much of that previously described by Barnett et al. [1991], Zhang and Levitus [1996], Tourre and White [1995], Giese and Carton [1999], Smith [2000], and Meinen and McPhaden [2000] in the way that anomalies of subsurface ocean heat content in the western Pacific develop as they progress eastward across the equatorial Pacific, often with a dipole pattern across the Pacific, AND THEN WITH ANOMALIES PROGRESSING OFF THE EQUATOR TO HIGHER LATITUDES. Zhang and Levitus [1996] found links only to the North Pacific, perhaps reflecting the available data, while our results reveal strong links to both hemispheres. The SST evolution lags somewhat behind that of the subsurface ocean and is damped by surface fluxes and transports out of the region by the atmosphere, emphasizing the dominant role of the surface wind stress and ocean dynamics and advection in producing the local ocean heat content and SST anomalies. This damping of the ocean signal, however, forces the atmospheric anomalies. MOREOVER, THIS ASPECT ALSO EMPHASIZES THAT IN COLD LA NINA CONDITIONS THE SURFACE FLUXES OF HEAT ARE GOING INTO THE OCEAN RELATIVE TO THE MEAN AND ARE WARMING THE OCEAN, ALTHOUGH NOT LOCALLY AS THE HEAT IS REDISTRIBUTED BY CURRENTS.”
SUMMARY
As discussed in the preceding, the warm water that fuels a traditional El Nino is stored in the Pacific Warm Pool. This warm water was “supplied” by the prior La Nina event. During an El Nino, that warm water travels east and is spread across the surface of the Eastern Tropical Pacific. Then during the La Nina that follows, the warm water is transported to the Western Tropical Pacific, where it is carried poleward and to the Eastern Indian Ocean by ocean currents. At the same time, during the La Nina, cloud cover over the Tropical Pacific decreases and Downward Shortwave Radiation (DSR) increases, warming the ocean surface more. Ocean currents carry this water to the Western Tropical Pacific, where it recharges the Pacific Warm Pool. At the end of the complete cycle of El Nino (discharge) and La Nina (redistribution and recharge), the Ocean Heat Content of the Tropical Pacific is restored (Figure 1) and sea surface temperatures have been raised.
In other words, Tropical Pacific Ocean Heat Content is regulated by the discharge, redistribution, and recharge of heat during El Nino and La Nina events. The heat that is released and the warm water that is redistributed during the traditional El Nino are “replaced” by the increase in Downward Shortwave Radiation during the La Nina. It appears that the redistribution of warm water during the La Nina and its impact on atmospheric circulation are overlooked when climate researchers attempt to account for the effects of ENSO on global temperatures, since they do not consider the dipole effect that takes place within the Pacific when they attempt to remove the effects of ENSO from global temperatures. Climate researchers assume the relationship between ENSO and global temperature is linear, when it clearly is not.
Figures 11 through 13 presented comparison graphs of East Pacific SST Anomalies and the SST Anomalies of the East Indian and West Pacific Oceans. For Figure 18, I’ve combined those two datasets and plotted them, listing them as East Indian and Pacific SST Anomalies. Assume for example that an ENSO event in total includes the combined effects of the El Nino and the subsequent La Nina, because the warm water released during the traditional El Nino continues to be redistributed during the La Nina. I’ve highlighted the points in Figure 18 at which the SST anomalies “equalize” before and after the major traditional El Nino events of 1986/87/88 and 1997/98 and their resulting La Nina events. I’ve also noted the approximate SST anomalies at those times. Over the multiyear period between the two ENSO events, SST anomalies for the combined East Indian and Pacific data (red) have remained relatively flat. They rose only ~0.02 deg C, from ~0.1 to 0.12 deg C, between mid-1990 and late 1996. And during the multiyear period after the 1997/98 and 1998/99/00/01 La Nina, SST anomalies have declined.
http://i48.tinypic.com/2enz2ac.pngFigure 18
But during the multiyear period of the 1986/87/88 El Nino and the 1988/89 La Nina, the East Indian and Pacific SST anomalies rose ~0.17 deg C, from ~-0.07 to ~0.1 deg C. And during the period of the 1997/98 El Nino and 1998/99/00/01 La Nina, the SST anomalies for the combined East Indian and Pacific dataset increased ~0.1 deg C, from ~0.12 to ~0.22 deg C. SST anomalies for the periods between and after major traditional ENSO (El Nino and La Nina) events either remain flat or they decline. But they rise during those major traditional ENSO (El Nino and La Nina) events. This is not a simple coincidence; causation is known.
I presented a number of reasons why the ENSO residuals (the apparent step changes) in the SST anomalies of the East Indian and West Pacific SST anomalies were important at the conclusion of my post “Global Temperatures This Decade Will Be The Warmest On Record…”. I’ll reproduce one here. Note that I’ve changed the Figure numbers for this post.
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The step changes bias the global SST anomalies upward and give the impression of a gradual increase in SST anomalies. This can be seen in a comparison graph of the SST anomalies of the East Indian and West Pacific Oceans, the SST anomalies of the “Rest of the World” (East Pacific, Atlantic, and West Indian Oceans), and the combination of the two, Figure 19. The period since 1996 is unique in the last 40+ years. There haven’t been any major volcanic eruptions to add noise to the data. This is why the data in Figure 19 starts in 1996.
http://i38.tinypic.com/2ezjk9s.pngFigure 19
Note how in Figure 19 the East Indian and West Pacific SST anomalies linger at the elevated levels while the SST anomalies for the “Rest of the World” are mimicking the variability of the NINO3.4 SST anomalies, shown in part in Figures 6 through 8. (That is, the SST anomalies for the “Rest of the World” are responding as researchers expect to both El Nino and La Nina events.) Over the next few years, ocean currents “mix” the elevated SST anomalies of the East Indian and West Pacific Oceans with the depressed SST anomalies of the “Rest of the World” oceans, dropping one and raising the other, until they intersect in 2003. This is more than 4 years after the end of the 1997/98 El Nino. Because the Global SST anomalies are a combination of the two, they are biased upward by the elevated East Indian-West Pacific SST anomalies and by the mixing with the waters of the “Rest of the World”. This gives the false impression of a gradual increase in global SST anomalies.
In other words, the effects of the major traditional El Nino events can linger for at least 4 years, causing gradual increases in global sea surface temperatures during that time. This gradual increase is incorrectly attributed to anthropogenic sources.
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Note that Trenberth et al (2002) serves as a wonderful resource when studying the effects of ENSO on global climate. However, the paper was written in 2000, published in 2002, and the data used in it stops in 1998. As illustrated above, the long-term effects of major traditional El Nino/La Nina events are best illustrated over the period of 1997 through 2001, because there were no volcanic eruptions to add noise to the data. Obviously, Trenberth et al could not have captured or discussed the long-term effects of that El Nino/La Nina event.
Also note that climate researchers attempt to remove the effects of ENSO events on global temperatures by subtracting scaled NINO3.4 SST anomalies (or another ENSO index) from global temperatures. They claim the rise in global temperatures that remains is caused by anthropogenic greenhouse gases. Refer to Figure 20. It should now be very clear that any attempt to remove the effects of ENSO in this way misses this dipole (seesaw) effect on the East Indian and West Pacific Ocean SST anomalies. One might think then that an index based on the SST anomalies of the East Indian and West Pacific Oceans could be created to capture this dipole effect and that this new index could be used to remove its linear portion from the global temperature record. Unfortunately, this will not work, because ocean currents and other coupled ocean-atmosphere processes “blend” the ENSO and dipole effects with other ocean basins. It also would not capture the effects of the warm waters that are supplied by the Pacific Warm Pool, which are not included in the SST anomalies before the El Nino event. Also, ENSO events are not created equal, and the response of global climate to ENSO events differs. Many El Nino events are pseudo-El Nino events, known as El Nino Modoki, and the response of global climate to El Nino Modoki are different that the response to traditional El Nino events. Refer to Ashok et al (2007) “El Nino Modoki and its Possible Teleconnection.” https://www.jamstec.go.jp/frcgc/research/d1/iod/publications/modoki-ashok.pdf
http://i34.tinypic.com/3589pj9.pngFigure 20
The papers that use this erroneous method are listed toward the bottom of my post Global Temperatures This Decade Will Be The Warmest On Record…, under the heading of “Papers That Portray A Linear Relationship Between ENSO And Global Temperatures”.
One last note, Trenberth et al (2002) acknowledged the existence of the residual effects of ENSO events. They wrote, “Although it is possible to use regression to eliminate the linear portion of the global mean temperature signal associated with ENSO, the processes that contribute regionally to the global mean differ considerably, and THE LINEAR APPROACH LIKELY LEAVES AN ENSO RESIDUAL.” [My caps for emphasis.]
And as illustrated in this post, the ENSO residuals from the 1986/87/88 El Nino and 1988/89 La Nina and from the 1997/98 El Nino and 1998/99/00/01 La Nina, account for most of the rise in global SST anomalies from 1981 to 2009, excluding the North Atlantic, of course, which is dominated by the Atlantic Multidecadal Oscillation).
SOURCES
In addition to the sources noted throughout the text, the others are listed below.
OI.v2 SST anomaly data is available through the NOAA NOMADS website:
http://nomad3.ncep.noaa.gov/cgi-bin/pdisp_sst.sh?lite=
NODC Ocean Heat Content and ISCCP Cloud Amount data are available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere
Ocean Surface Current Maps are available through the NASA Ocean Motion and Surface Currents webpage:
http://oceanmotion.org/html/resources/oscar.htm
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