Guest post by David Archibald
Bob Tisdale’s post on ENSO on 19th November prompted me to see what I could find in the Southern Oscillation Index (SOI) data. The SOI is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. Sustained negative values of the SOI often indicate El Nino episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the Pacific Trade Winds, and a reduction in rainfall over eastern and northern Australia. Following is a graph of the SOI on a monthly basis from 1876 to 2010. The major El Ninos are discernable, otherwise it looks like a lot of noise.
The graph following shows the cumulative monthly SOI from 1876 to 2010.
The SOI does tell a story. It was non-trending for the last of the Little Ice Age and then from 1920 went into a long La Nina-dominated trend that ended with the Great Pacific Climate Shift of 1976. The planet warmed into the 1930s at the beginning of this trend, but then cooled, as it should have down in a La Nina-dominated trend, from the 1940s to the 1970s.
The subsequent El Nino-dominated trend from 1976 to 1995 was almost three times as fast as the rise. The Climategate emails show that Phil Jones was aware that global warming ended in 1995. The end of the El Nino-dominated trend in 1995 might be the physical cause of that cessation of warming. The SOI has been non-trending since.
This might have been a very neat story if the world had cooled instead of warmed into the 1930s. The 20 years of El Nino-dominant trend from 1976 to 1995 produced the late 20th century warming that got so many people hot and bothered. The story told by the SOI also reinforces how important the Great Pacific Climate Shift of 1976 was. The climate system turned on a dime for some as yet unknown reason.
Sorry, clear as mud. I sort of get your point, but I am not clear how you got from SOI to your point. Maybe I am being thick, but maybe not? A little more explanation would be helpful, please and thanks.
The graph showing the cumulative SOI is interesting, and suggestive. However, as you point out, the world was getting warmer during the 1930s despite the La Nina-dominated trend. Are you suggesting that there was 10 to 20 year lag between changing SOI and changing teperatures? If so, have you any ideas why there would be such a long lag period?
Second question: how can you be sure that the 1976-1995 period of El Nino dominated trend was responsible for the warming and was not just the way warming got expressed? In other words which arguments do you have that it was the primary cause?
“for some as yet unknown reason”
Sigh. A real scientist speaks. Thank you, David Archibold.
If you ask me, it is a lot of noise. Here is a suggested test – take the notation off that SOI index graph i.e remove the “1998 el nino”, “federation drought” etc, and hand it to someone who does not know when those incidents occurred. Do a blind test. Ask them to tell you which are Australian drought years…. do you think they will succeed?
Hasn’t it been suggested that the best correlation comes from the Indian Ocean Dipole , not SOI?
Dr. Archibald
Recently I plotted diagram of five various events (independent of climate/temperatures) which I characterised as the North Pacific Gateways as shown here:
http://www.vukcevic.talktalk.net/NPG.htm
You will note that blue line is in a good agreement with your cumulative monthly SOI, with my graph about 10-12 years in advance to the cumulative SOI.
Also you may notice that the red line has a close correlation with the PDO, again with about 10-12 years advance.
Antonia says:
December 9, 2010 at 12:35 am
“for some as yet unknown reason”
Sigh. A real scientist speaks. Thank you, David Archibold.
Well it may not stay ‘unknown for too long’, now that I am aware that one of my graphs (see my post above) matches Dr. Archibald’s cumulative monthly SOI.
No disrespect but this seems to explain nothing.
Thanks David for soome interesting ideas.
From memory 1976, was a year of several bad earthquakes and a new volcano, I think. Perhaps worth a look for sudden LOD changes that year?
How is the ‘cumulative monthly trend’ calculated ?
David Archibald wrote, “It was non-trending for the last of the Little Ice Age and then from 1920 went into a long La Nina-dominated trend that ended with the Great Pacific Climate Shift of 1976.”
That’s one of the differences between the SOI and NINO3.4 SST anomalies. I recreated the ONI Index table using HADISST NINO3.4 SST anomalies in this post…
http://bobtisdale.blogspot.com/2010/11/long-term-oni-like-table-of-el-nino-and.html
I then did a quick count of El Nino versus La Nina events, and it contradicts your statement. Keying off the development year, during the period from 1910 to 1944, there were 10 El Niño events and 6 La Niña events. (For this simple comparison, if an El Niño or La Niña event extends from one winter to the next, it would be considered two events.) From 1945 to 1975, there were only 7 El Niño events, compared to 11 La Niña events. And from 1976 to present, El Niño events dominated again. There were 12 El Niño events but only 8 La Niña events.
Aahh, the summer of 76, fond memories of hazy summer days during endless school holidays, picnics and trips to the seaside.
Can we have some more please?
“It was non-trending for the last of the Little Ice Age and then from 1920 went into a long La Nina-dominated trend ”
Please keep in mind that during a La Nina phase, the ocean is actually absorbing heat. So while the surface temperature is lower because of the stronger trade winds, the reduced cloud cover is actually allowing more solar radiation to reach the water.
So increased La Nina events means the Pacific was actually accumulating energy during that period. Notice how the graph makes a sudden drop at around 1933. That is the ocean giving the heat up to the atmosphere. It then continued accumulating heat until 1975. At that point the ocean began to give up heat to the atmosphere. If I am right, we should see a corresponding slackening of the trade winds since 1975 and an increase in tropical pacific clouds.
Now the Pacific is dumping heat to the atmosphere. Until about 1998 or so and since then it has been about neutral. And looking at the various SST graphs you can see that. We had a significant La Nina in 2007/2008 followed by a significant El Nino .. they cancel each other.
wilt says:
December 9, 2010 at 12:31 am
No, I don’t believe in big lags in the atmospheric climate, so the warming of the 1920s and early 30s may have been due to another factor – the Sun did become more active. On your second question, I am not saying which follows which, and I am not arguing that it is the primary cause.
I was originally motivated to produce this graphic by Bob Tisdale’s observation that some heat or cooling remains in the system from each ENSO event. In the broad, that observation is borne out by this graphic. Perhaps, in the long term, El Ninos and La Ninas do balance out. In our 134 years of data, we have a non-trending steady state situation, then 56 years of La Nina-dominant followed by 20 years of El Nino-dominant – taking it back to where it came from. It could have stopped short, or it could have overshot – but it didn’t.
Antonia says:
December 9, 2010 at 12:35 am
Thankyou. I was thinking that I wouldn’t be the one to propose a reason for the Great Pacific Climate Shift of 1976. But I am not a believer in random walk in climate. Perhaps the SOI or whatever causes it got locked into a long run state, and 1976 was when the system broke trend and started reverting to normal.
HR says: December 9, 2010 at 1:17 am
No disrespect but this seems to explain nothing.
Totally disagree; combined with my graph (blue line)
http://www.vukcevic.talktalk.net/NPG.htm
(taken along 5 degree south parallel) would explain a great deal for the climate science.
“The story told by the SOI also reinforces how important the Great Pacific Climate Shift of 1976 was. The climate system turned on a dime for some as yet unknown reason. ”
I don’t know if it was just a coincidence but 1976 was the year that Britain experienced a summer that broke all previous records. According to Wikipedia:
“In the Central England Temperature series 1976 has the hottest summer for more than 350 years and probably for much longer. ”
http://en.wikipedia.org/wiki/1976_United_Kingdom_heat_wave
Since 1976 there have been a few summers that could be compared with it and I think that is one of the main reasons why the majority of the British population came to accept the idea that human activity is changing the global climate.
Perhaps if the SOI continues along a similar path to the last few years belief in AGW will decline.
David
Can you link to the original data that you used for SOI and also can you tell us how the “cumulative monthly SOI” was calculated?
This was around the same time the Salinity on the surface of the oceans started accumating.
Interesting…
vukcevic says: December 9, 2010 at 1:05 am
Dr. Archibald Recently I plotted diagram of five various events (independent of climate/temperatures) which I characterised as the North Pacific Gateways as shown here: http://www.vukcevic.talktalk.net/NPG.htm
Pretty colors.
Needs labels.
David Archibald says: “I was originally motivated to produce this graphic by Bob Tisdale’s observation that some heat or cooling remains in the system from each ENSO event…”
And the leftover warm water from El Nino events gets spun up into the Kuroshio-Oyashion Extension by the North Pacific gyre, and releases heat once again, but this time at Northern Hemisphere mid latitudes during the La Nina, assuming a La Nina follows the El Nino. And this secondary release of heat helps explain the upward shifts after major El Nino/La Nina events in:
— North Atlantic SST anomalies,
— Northern Hemisphere TLT anomalies north of 20N, and
— Land plus Sea surface temperature anomalies (GISTEMP LOTI) between 20N and 65N.
http://bobtisdale.blogspot.com/2010/12/enso-related-variations-in-kuroshio.html
Bob Tisdale says:
December 9, 2010 at 1:42 am
My graph gets away from counting events and uses the cumulative SOI value. Not all El Ninos and La Ninas are created equal. This way we compare apples with apples.
crosspatch says:
December 9, 2010 at 1:57 am
Thankyou. That may explain why the El Nino trend stopped. The oceans are back to no excess heat.
John A says:
December 9, 2010 at 2:35 am
ftp://ftp.bom.gov.au/anon/home/ncc/www/sco/soi/soiplaintext.html
That’s the link. If you email me, I will send you my Excel file on the SOI. david.archibald @ur momisugly westnet.com.au
I don’t know how the graph was plotted but I would guess it is a straightforward cumulative sum of differences (CUSUM) graph which is one of several standard methods of treating a time series. The way I would do it (the author will have to confirm or deny this) is to treat the series as a retrospective analysis.
That is: obtain a set of data, then carry out a grand overall assessment rather than doing it year by year as a running assessment. Both methods could be used and have different methods of interpretation. The running assessment allows you to determine (to within statistical limits) whether a significant change in the value has occurred while the data is coming in.
For a retrospective assessment I would find the grand mean. For each annual point subtract the grand mean and add it to the cumulative sum of differences for all previous years. Repeat this for all the annual figures and you will have a series of ups and downs with the graph eventually being forced to return to zero (a little thought will show this has to be the end result).
The graph can be interpreted as follows:
If a series of annual values is above the grand mean the graph will climb. If the values are the same as the grand mean for a number of years the slope will be horizontal. If a series of values is below the grand mean then the graph has a negative slope.
My simple eye-ball interpretation of the graph (assuming it is a retrospective CUSUM) is:
1876-1916 The SOI values were all close to the grand mean
Around 1916 something happened to produce a step change in the (local) mean
1916-1976 The mean of the SOI stayed constant at a higher value than the grand mean. The grand mean can be calculated from the slope
Around 1976 something happened to produce a step change (reduction) in the mean
1976-1995 The (local) mean value changed to below the grand mean for 20 years. Again, the value can be calculated.
1995 Again something changed to shift the local mean of the SOI back to the grand mean.
1995-end of graph The SOI has returned to the grand mean.
Thus, it is the slope that matters and what you are seeking is to see whether one or more of the series of (apparently) constant local-means is different from the grand mean.
There is a formal statistical test that is outlined by the UK BS on CUSUM analysis to determine whether the changes are significant or not.
My suggested interpretation above is my guess. A proper analysis would need to be carried out but is far from arduous once the data is obtained. The calculations are easily managed by a simple spreadsheet.
I still think it looks like noise, but, hey let’s try a hindcast.
Can someone, preferably someone who does not know the answer, look at the SOI graph and tell me what the weather has been like in eastern Australia for the past 10 years.
David Archibald says: “My graph gets away from counting events and uses the cumulative SOI value. Not all El Ninos and La Ninas are created equal. This way we compare apples with apples.”
Which is why I usually use a 121-month running-average filter of NINO3.4 SST anomalies to show periods when El Nino and La Nina events dominate:
http://i54.tinypic.com/33di5qr.jpg
And that agrees with my simple analysis described above.
Regards
I find it interesting that El Ninos almost always have a stronger influence on global weather patterns than La Ninas.
I also think that if ENSO was a product of TSI or cloud cover, long term ENSO predictions would have been more accurate than they are now.
The “usual” conditions in the pacific is for the waters in the eastern pacific, near Peru, to be generally 8DegC COOLER than it’s latitudinal position would indicate. This is because of the cold ocean currents flowing up the coast of Chile, upwelling near Peru.
When this upwelling slows, the surface waters warm quickly = EL Nino. The more dramatic this slowing, the stronger the El Nino. It’s effects are well known, floods in South America, droughts in Australia and North America and an increase in global temperatures.
When the upwelling speeds up, the surface waters cool back down, higher than normal speed = La Nina
The upwelling is the result of the thermohaline circulation, a phenomenon we know little about. I recall reading somewhere that there were many sensors released recently into the oceans to track the thermohaline circulation. If and when we get a handle on what makes this circulation tick, we’ll be able to predict ENSO events quite accurately.
Caveat: Though solar insolation or cloud cover do not cause ENSO events, they may well modulate the strength of these events. High insolation during El Nino strengthens it, low insolation weakens it. Vice versa for la Nina.
These are what I accept regarding ENSO events. I got my information from the web site of the late John L Daly HERE and HERE and many many other articles John posted about ENSO
regards
Dr. Archibald
In this graph I superimposed your SOI cumulative graph with data for the ‘Pacific Gateway’(independent of climate / temperature events) located along 5 degree South parallel.
http://www.vukcevic.talktalk.net/SOI.htm
Only significant disagreement is about 10 year period around 1960, which I do not consider significant for reason of the nature of the ‘pacific gateway’ data.
Dr. Archibald thank you for bringing the SOI cumulative to my attention.