ENSO forecast based on tidal forcing with an Artificial Neural Network
Investigation submitted by Per Strandberg
Here on this page, you are going to find evidence that tidal forcing is one of the most important, if not the most important driver for ENSO variations. That tidal forcing could be the main explanation for ENSO variations was something I stumbled upon when I examined possible ENSO drivers.
After the previous results which I got when I was using an Artificial Neural Network ANN and where I did an analysis of the correlations between the global mean temperature and possible forcing drivers, which can be viewed here, I turned my attention to the ENSO index by looking into the Multivariate ENSO Index (MEI).
One thing I found when I analyzed the result from correlations to ENSO was that there is a strong correlation between variations in Earth’s rotations both to the global mean temperature and to the ENSO index. What we are talking about here are small variations in Earth’s rotations, which are in the order of milliseconds.
One other factor with correlation to the ENSO is of course SOI, but I also found correlations to SST, PDO, and the Kp and Ap indexes.
From this, I concluded that either it is ENSO which is driving changes in Earth’s rotation or it changes in Earth’s rotation, which is causing variations in ENSO or more likely it is some combination of both.
Proof that ENSO and variations of Earth’s rotation are proportionally correlated to each other has been known for some time. This can be seen here.
The mechanisms which tie ENSO and variations in Earth’s rotation together are caused by sea current changes, changes in trade winds or by displacements of water between the equator and slightly higher latitudes. This all makes sense.
The water currents in the northern hemisphere follow a clockwise pattern, and in the Southern hemisphere they follow a counterclockwise pattern because of the Coriolis effect. The trade wind and the currents near the equator are moving to the west. However the Current closest to the equator called the equatorial counter current move to the east. Still deeper at depth down to 200 meters at the equator an ever stronger current is moving to the east.
The behavior of this current of the Equatorial Pacific is shown on this page by Bob Tisdale.
The only mechanism by which ENSO can be driven by changes in Earth’s rotation is by variations in the tidal force.
My next step was to try to include tidal forcing in my ANN.
I then got three problems, which I had to overcome.
Firstly: I had to find data over the position and distance to the Moon and to the Sun. Eventually, I found software from which I could get this data, although it gave limited information and I was only able to print out time and position when the Sun and the Moon were closest and farthest from the Earth and with the Moon I could also calculate the time and position of the new moon, the full moon and the moon nodes. The Moon nodes are the location where the Moon cross over the ecliptic plane.
Secondly: I had to find the formula for the tidal force vector and implement this into my software.
Thirdly: I had to figure out what features in the tidal forcing which could affect ENSO. I had to experiment with different configurations based in my limited and rather crude data. To do this, I had to make complicated trigonometrically calculations in order to get the right value of the tidal force. Eventually, I got good correlations between ENSO and the tidal forcing. By this time, I had figured out which features in the tidal forcing that were causing this correlation. However it was not a direct correlation with ENSO, rather it was a correlation with the derivate signal of ENSO, i.e. it was affecting the rate of change of ENSO. The correlation to the change of rate in Earth’s rotation, on the other hand, is direct. This means that tidal forcing is causing the rate of Earth’s rotation to either speed up or speed down. The rate of rotation is then responsible for changes of the ENSO index. One reason was that it was difficult to identify, which features, which cause correlations. This was because each tidal forcing point I use the sum of monthly calculations. The size of the tidal forcing changes each and every day and how to summarize this data the right way into useful functions, which can be used to construct values that could create good correlations were difficult.
Of course, the tidal force is not the only factor which drives ENSO, but it is the most influential factor.
To test if that would be the case I ran my network with the right tidal forcing data. I also included feedback loops back in the network from the output ENSO values to some of the input nodes. After some testing and individual adjustments of the internal components in the artificial network, I got good results. Following on my earlier experiment of the ANN on the mean global temperature I trained the ANN from late 1978 up to the end of 2004. I used the time from 2005 up to the late 2011 for test the calculations, in order to find the minimal error function.
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This is the result I got. The exciting thing with this result is that it is possible to make forecasts for much longer times into the future. Today’s predictions use computer models and are only able to make credible predictions 4 to 5 months into the future. While in my case, using my ANN calculations based on tidal forcing can be made for forecasts for an almost unlimited time because the Moon and Sun’s positions into the future are known in advance. Although, I have to stress that with the predication so far it is not possible to get the last figure right. Currently, it is only possible to make an estimate with a relative high likelihood at any date if ENSO are going to be positive, negative or neutral. However, as can be seen here the predictions are not always correct. The main large El Niño events of 1982 and 1998 can clearly be seen, but the large magnitude of these events can not be predicted.
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I later made a ENSO forecast from late 2011 up to 2020. I cannot show the result here because of proprietary reasons. This picture shows the test period and some of the forecast which ends in early 2013.
Note, however that the calculations from this graph, the ENSO index uses ENSO feedback values which all are from estimated ones. Those are not the real ENSO values.
Now Look at: the previous graph with the whole time span from 1979 up to 2011! On this graph, look at the beginning at the 3 first years from the start of 1979. These 3 first years have all exceptional good correlation to the real ENSO values. The difference with the start values in this case is that I use real ENSO values for the feedback values in the network calculations which are going into the calculations with values before the graph begins. This is because in my ANN, I use for every calculation point values which goes 3 years back in time and I must use real input values for values before my first calculated value.
If I would make a forecast for the next years using current real ENSO values from 3 years back and up to the current date, my forecast would be greatly improved and would be much better than forecast made with current computer models. There were 2 important events that happened the years just after 1979. The first was the eruption of El Chichon in 1982 in Mexico. The second was the unusually strong el Niño event between 1982-1983.
My calculated values after 1982 of ENSO tend to come out of phase after and around 1982, and the ANN seems not to be able to handle strong El Niño’s very well. After some years, the estimated ENSO value deteriorate somewhat mainly because of errors in the feedback caused by the inertia in Earth’s rotation. In contrast to computer model forecasts, I don’t use data from the Tropical Atmosphere Ocean TAO network which is a NOAA measurement network of buoys in the tropical Pacific that deliver real time data which feeds these ENSO models with real time data.
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Here is a result from the same program, but as input it uses variations in the Earth’s rotation instead of tidal forcing. As you can see, the correlation to the Earth’s rotation makes the result much better. However in contrast to tidal forcing, future changes in Earth’s rotation is unknown.
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Here is another graph from the same program with feedback but this time the input signal is only from SOI Southern Oscillation Index. As expected SOI is closely related to ENSO.
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Here is a repeat with the same program, but this time with a combination of tidal forcing, changes in Earth’s rotation, SOI, Kp and the Ap indexes. As you can see, this result is similar to that of the previous with only SOI.
The next step I plan to take is to use the ANN with real time data and make more accurate ENSO predictions for the next 3 to 4 years in to the future. I also want to test with real ENSO input data for several time periods in order to evaluate statistically how the good predictions can be based on real time ENSO feedback input data for the beginning.
After that, I want to improve on my result by using more precise and accurate tidal calculations. I have found a program from which I can make precise calculations of the Moon and the Sun on a daily basis. Other factors I plan to look into are the mechanism of the Kelvin wave, Walker circulation and MJO which all should influence ENSO to some degree.
So far I have only looked at ENSO. I can easily switch to SOI, NOI and changes in Earth’s rotation and use that as an output for predicting ENSO with the ANN.
Conclusion from my result is that tidal forcing is as a major factor in ENSO forcing. I now have gotten new questions. Compared with other causes how important is the effect from tidal forcing? Is it possible to find an increasing effect from tidal forcing by improving the tidal data I use? Is it, for example, possible to identify tidal forcing as the cause for the strong El Niño of 1982 and 1998?
It may be possible to get better ENSO results by using predictions based on SOI, NOI, Earth’s rotations or by starting from tidal forcing only. I’ll test and see. Also, ENSO and SOI are parameters for which there exists long historical data records. By, using a longer time span for training and testing, the accuracy of predictions based on ANN should be improved.
I acknowledge that it is not easy to find correlations between tidal forcing without testing out the right feature and by using am ANN. However I do find it very strange that no scientist to my knowledge has been looking into a possible connection between tidal forcing and ENSO in any depth.
As can be seen from what the IPCC writes about ENSO predictions, they do not have a clue. The current data models that are in use can only predict with any accuracy 4 to 5 months into the future. When it comes to the ENSO drivers, these researchers think chaos theory and random noise are the mechanisms which explains the causes of ENSO changes.
However Cerveny, R. S. and J. A. Shaffer (2001) et al. in the report, The Moon and El Niño, Geophys. Res., writes about the Moon cycles and ENSO, where they find correlations between the solar cycles and ENSO.
To me at least, it seems that the solution to long range ENSO prediction has for a long time been right in front of the eyes of these researchers, but nobody has taken up the challenge to figure it out.
I see the same reason why the climate community at large has not studied tidal forcing as an explanation for ENSO variations and why none TSI solar forcing as an additional cause for climate forcing ignored. The primary reason is that they have had their education in meteorology, atmospheric physics, thermodynamics or in computer science. Most of them are specialists in a few narrow disciplines, and as such they prefer only to apply knowledge from the fields they know. They are not generalists and display strong resistance for applying knowledge from other area from which they lack knowledge. Then add to that group thinking, peer pressure and lack of funding for research in alternative causes of climate change and this explains the current one-sided situation. This is one of reason that predictions made with computer simulations are failing.
ANN are seldom used in climate science. There are some exceptions. One is research done by Dr William Hsieh from the University of British Columbia who uses this technique for ENSO predictions, but to my knowledge without using any tidal forcing. To learn more about how ANN works and how I have implemented this technique in climate investigation, Click here
agfosterjr says:
January 23, 2013 at 1:16 pm
Any tutor would help. Your knowledge is extremely limited, and your assertions have no merit.
Some perhaps relevant info to this discussion here:
http://www.lhup.edu/~dsimanek/scenario/tides.htm
“The tidal bulges are very small, seemingly insignificantly small, compared to the radius of the Earth. But over the huge area of one of the oceans, the tidal bulges alone still raise a huge amount of water. We have discussed these using the conceptual model of a stationary Earth-moon system without continents, but with a uniform depth ocean covering its entire surface. We do this to emphasize that these tidal bulges are not due to rotation, but simply to the variation of the moon’s gravitational field over the volume of the Earth.
When we add continents to this model, the ocean bulges reflect from shorelines, setting up currents, resonant motions and standing waves. Standing waves of a liquid in a shallow basin have regions of high amplitude variation (antinodes) and regions of zero amplitude variation (nodes). So it’s not surprising that in oceans we see some places where the tidal variations are nearly zero. All of this ebb and flow of water volume affects ocean currents as well. Yet it is all driven by the tidal forces due to the moon’s changing position with respect to Earth. Still, it’s amazing that Newton was able to use his new ideas about gravitation to provide the first correct explanation of the dynamical relation between the moon and tides.”
Cheers, 🙂
Shawnhet says:
January 23, 2013 at 2:04 pm
Yes, modes of oscillation due to the shape of the ocean basins are part of the puzzle. The important thing to remember is that, even when motions appear relatively small, when considered over the vast expanse of the oceans, the energies involved are immense. Thus, a particular avenue for energy flow cannot be summarily dismissed without putting numbers to it.
Thanks Shawn–here’s another: http://oceanmotion.org/html/background/tides-ocean.htm
–AGF
Being 92% efficient with an 1883 meter head, the Swiss Bieudron turbines spew out water .35 degrees C warmer than the head waters. (At zero efficiency it would be 4.5 degrees C warmer–with a 6160 foot head.) Water going over Niagara Falls heats up .14 degrees C assuming total conversion of potential energy to heat (in fact some energy goes towards erosion). So at grossly exaggerated heights and assuming totally irreversible processes we still have barely measurable effects on temperature.
The sun does most of the work. –AGF
agfosterjr says:
January 24, 2013 at 7:37 am
May or may not be. You can look through the discussion and see that I’ve never been categorical. But, your examples fail to capture the dynamics we are talking about. Nutation stores energy, it can accumulate over time. When released in waves, it can alter temperatures dramatically in cyclical fashion.
It would take some very involved analysis to determine just how much, but the signal for which we are seeking a cause is a mere +/- 0.2 degrees in the approximately 60 year climate cycle observed in the surface air temperatures. That cycle is what reinforced the longer term warming from the LIA in the latter third of the 20th century, leading to the AGW panic.
Believe it or don’t, it doesn’t matter to me. But, the possibility remains, and we have established that your earlier hubris in rejecting it outright was ill founded.
1. Nutation is fairly constant. How can any climate cycles be correlated to constant nutation?
2. Nutation involves energy transfer to the ocean of many orders of magnitude less than that of fortnightly tides, which are much weaker than diurnal tides (as far irreversible energy dissipation is concerned), which in turn are much weaker per volume than Niagara Falls.
You have not even tried to make a case for nutation. All you have done is referenced a crackpot paper. Have you no BS detection skills whatever?
–AGF
After repeatedly being shown to be wrong, you remain pugnacious and ungracious. You haven’t a clue how the system works, and I am fed up with your incivility.
OK, genius, here’s a problem for you. The earth has a moment of inertia of 8×10^37 kg m^2, and has a deceleration of 2.3 ms/century (all tidal: earth, water, air–forget the air). The ocean has a volume of 1.3×10^9km^3. Assuming all this energy goes to the ocean (and most of it does one way or another), figure out for us how many degrees a century’s worth of tidal dissipation would heat the ocean if all were delivered at once. –AGF
The earth has a kinetic energy of rotation of 2.14×10^29 J = 5.1×10^28cal. A mean solar day is 86400 seconds long. .0023sec/86400sec = 2.66×10^-8. 2.66×10^-8 x 5.1×10^28 cal leaves 1.36×10^21 cal/century to heat the ocean. (Sea water has a specific heat capacity of about 5% less than fresh water.) The ocean contains 1.3×10^24 ml of water. So, 1.36×10^21 cal / 1.3×10^24 ml = 10^-3 degrees/century of ocean heating by tidal friction–one thousandth of a degree, if I haven’t screwed up anywhere.
It goes without saying that nutation is an inferior byproduct of rotation, and that nutation cannot possibly deliver energy which is not a function of angular momentum. Terrestrial nutation corresponds to lunar nutation, and seems to be in fact a variation in precession caused by variation in the moon’s orbital inclination to the earth’s axis. Which would mean it is not analogous to the nutation of a solid spinning top, and neither is analogous to the sort of nutation involved with flexible parts of a rotating spacecraft. I suspect that Chandler Wobble better corresponds to the nutation of a spinning top–I’ll leave it to an expert to clarify that. –AGF
Off by a factor of two, I do believe, seeing as kinetic energy is a function of the square of the angular velocity, unlike the momentum. So, two thousandths of a degree per century is a better estimate than one, although taking into account the unknown ratio of earth to ocean tidal heat, the truth must be somewhere between 1.5 and 1.9 thousandths of a degree. –AGF