Question
Asked 12th May, 2015

Why is Earth rotation accelerating?

Since VLBI measurements started, four decades ago, Earth’s rotation has been accelerating
The length of the day displays a trend in the order of -6 ms/cy, which is relevant. The tidal effect contribution to Earth rotation that corresponds to the expansion of Moon’s orbit (considering that this expansion is totally due to tidal effect) is +2.3 ms/cy. There is also an estimated contribution due a post glacial rebound of -0.7 ms/cy. So, the difference between measured and expected values for the variation of Earth rotation in the last four decades is in the order of – 8 ms/cy. What can be the cause of this?

Most recent answer

8th Jan, 2022
Anton Vrdoljak
University of Mostar
Happy Earth's Rotation Day, everyone!
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All Answers (21)

12th May, 2015
Bhushan Bhoja Poojary
NIMS University
2004 Indian Ocean earthquake, have caused the rotation to speed up by around 3 microseconds by affecting the Earth's moment of inertia.
1 Recommendation
12th May, 2015
Alfredo Oliveira
Bhushan, that was a value calculated by geophysicists, considering that the Indian ocean tectonic plate went underneath Indonesian one; measurements of Earth rotation, however, do not seem to support it. The earthquake was a complex phenomenon, with structures going down and others going up. But your observation gives a lead: this sustained acceleration of Earth rotation may be due to a slow going down of continental plates? This links this question to another: https://www.researchgate.net/post/Are_the_oceans_rising_or_are_the_continents_going_down_How_can_we_know
2 Recommendations
12th May, 2015
Bhushan Bhoja Poojary
NIMS University
Hello Alfredo,
This article might also be intresting for you to read.
Earth's 6-Year Twitch Changes Day Length
Regards,
Bhushan Poojary
2 Recommendations
12th May, 2015
George E. Van Hoesen
self
I think that there are several contributing factors.
I am not an expert but I understand the Physics behind the issue very well.  As we work on a better model of the universe and gravity we will have a better understanding of how to correct problems like this.  Climate change is nothing compared to what this means for the end of the humans on earth.
One is that the earth is slowly spiraling into the sun.  Even though it will take it several billion years to do so the decrease in orbital distance increases its speed will change with the affect.
As the moon get further from us its grip on the slowing of the earths rotation increase in velocity is less and therefor it will change the speed at which the earth spins.
Although these affects are very small the problem is that they are increasing or should be increasing at an increasing rate.  In the next thousand years these affects could be much greater.  As a planet that will unless we find a way to stop it will fall into the sun someday, we should be working on this issue with some vigor.     
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12th May, 2015
Alfredo Oliveira
Dear Bushan, its an interesting analysis, thanks. Yet, the goal of that analysis was to find a link between magnetic events and Earth rotation, the trend of Earth rotation being irrelevant for it and ignored; and is precisely the trend that is at question here. In the figure attached you can see that trend. Note that data before the 70's was not obtained from VLBI or satellites and is questionable. 
One important consequence of these measurements is that now there is no support to the theory that Moon is receding from Earth is due to the tidal effect - it does not contradict it, but it is not also an evidence of it as it would be if Earth rotation was slowing down in the order of 2ms/cy; instead, Earth is speeding up at a rate that reveal the existence of unsuspected phenomena. So, there is here a rather interesting field of research.
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12th May, 2015
Alfredo Oliveira
Dear George
You know, you are an optimist... we have a dramatic event to face in a not so far future. Do you know the Great Extinctions? Dinosaurs and so? Although that is not usually mentioned, they are rather frequent events, the last one happened at 12900 years ago. According to genetic calculations, only about 10 000 humans survived it and in some places, like the north america, they were fully extinct. This is was one event of small intensity compared to the one that extinct dinosaurs; the ones of larger intensity occur at time scales of tens of millions of years, the "lower" intensity ones at tens of thousands of years.
Many causes have been appointed to these events because none can explain them - nor meteors, or Earthquakes, or volcanic activity, or supernovae explosion, etc. Not even all these causes together are able to explain the extreme violence of these events. The cause is another. This certainly is an issue on which we should be working with some vigor, in this point I full agree with you.
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12th May, 2015
George E. Van Hoesen
self
Alfredo,
I am not an optimist.  I am sort of a realist.  I know that if I jump up and down and scream no one will listen to me.  I am however very concerned that we are not doing more to insure the survival of the human race.  I can say that I am concerned that we can not work fast enough to get what needs to be done done.  Yes there will be another mass extinction event and know one can tell when.  
There are so many things in science that that need to be fixed and I sometime wonder if we will ever make it.  The issue is not if something is going to happen but how much time will we have to know that it is going to happen.  I just hope it is not that we wake up to the earth in a disaster one day soon.  
Now that I have scared everyone.  It could be a million years from now as easily as it could be tomorrow.  This being said it is time to work on solutions to how to make things better.
12th May, 2015
Alfredo Oliveira
George
I have discovered that it is not the space that expands but matter that is evanescing in a self-similar way; as our units are intrinsic to matter, decrease with it, we measure invariant matter and an expanding space. This is similar to what happened with the apparent rotation of the skies, space expansion models being just a modern version of Ptolemy model. Many cosmologists know my work but they fear that, like Newton's work, my work will "kill" present cosmology, destroying their careers. And some have emailed to me saying that, and saying that they will never accept my work because it is not of the interest of the scientific system. The scientists in Galileu time did the same.
I have discovered it more than twenty years ago; and from that I have discovered a lot of things about the universe - like Newton's work, my work opens a great window over the universe. One of the things I discovered is exactly the phenomenon that causes the extinctions; and, differently of what you may think, we can define a time window for its next occurrence. 
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19th May, 2015
Wolfgang R. Dick
Federal Agency for Cartography and Geodesy
Dear Alfredo,
A possible mechanism for accelarating Earth rotation is core-mantle coupling. Tidal friction, which decelarates the rotation, has an effect primarily on Earth's mantle, whereas the core may rotate with the same rate as before. Through core-mantle coupling the core may then accelerate the mantle again, but finally the mantle will decelerate the core also through core-mantle coupling. But as far as I know, there are no detailed investigations into modelling such a process and comparing with observations.
Best regards,
Wolfgang
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19th May, 2015
Alfredo Oliveira
Dear Wolfgang
Yes, thanks Wolfgang, certainly that gives a contribution to Earth rotation. Is this contribution enough? What other phenomena can contribute?
Let's start a list:
1- core-mantle coupling
More contributions to this list?
11th Jun, 2015
Ch. Bizouard
Observatoire de Paris
Dear Alfredo,
On time scale of some decades, and this precisely what you mention, the lenght of day varies up to 1 ms in 10 years or  10 ms/century. But this rate is only constant over some years, with fluctuations taking place over periods of ~14,  ~30 and ~70 years.
Long term increase of the lenght of day of ~1-2ms / century cannot be confirmed by modern astro-geodetic data, for its time scale is about 2 century. Only past astrometric observations (lunar occultation Sun elipses) afford to determine this kind of rate.
On shorter time scale, you see what is believed to be caused  by mass transports within the fluid core. Though, the fluid core remains the "dark matter" of geophysics, its mass redistributions or its coupling with the mantle are  manifested indirectly. Some authors, like Sidorenkov, have proposed alternative explanations, associated with hydrologic transports.
Christian Bizouard, Earth rotation service of the Paris Observatory
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12th Jun, 2015
Alfredo Oliveira
Dear Christian Bizouard
Thanks for your contribution. It shows that taking conclusions for such a short record in what concerns geological phenomena is totally impossible. Yet, this record has a great importance - the one of revealing our presumption on Earth rotation: the presumption that the rotation speed is decreasing due to Lunar tidal effect.
Past astrometric observations are very questionable  - the error margin in enormous and the model used to analyze data presumes also a number of things, like the invariance of orbits. This presumption biases analysis and conclusions. For instance, many persons think that current ephemerides analises show that orbits are invariant when it is not so - the only thing that can be concluded is that they are compatible with invariant orbits, but they are also compatible with varying orbits and that is not stated - the error margin and the huge number of the parameters of the model (around 230) do not allow to conclude more than that.
The best example of this presumption is perhaps the fact the it has been stated that leap seconds are a consequence of the slowing down of Earth rotation, when they are the consequence of a definition of second that was too short for the time when it was defined.
If one drops that presumption, other phenomena emerge, for instance, Earth inner temperature is not constant and this has several consequences, and all imply a varying Earth radius and varying rotation speed. Other phenomenon is the vertical oscillation of the mantle; and the fact that oceans are steadily rising for more than a century may trace a downward motion of continental plates, due both to that oscillation and also to solidification of the mantle under continental plates due to the decrease of internal temperature.
So, as I see things, all analyses relative to data prior to VLBI measurements are not reliable; to analyze Earth rotation one must consider only recent data and look for phenomena that can be directly related with it, like the variation of oceans' level in relation to coast, the satellite measurements of position of Earth stations, the analysis of Earth internal temperature. All this is critical to understand how Earth is evolving.
15th Sep, 2015
Wolfgang R. Dick
Federal Agency for Cartography and Geodesy
Dear Alfredo,
Recently I met Richard Gross and asked him your question. He recommended his review paper which appeared in a 2nd edition this year:
Gross R.S.: Earth Rotation Variations - Long Period. In: Gerald Schubert (editor-inchief) Treatise on Geophysics, 2nd edition, Vol 3. Oxford: Elsevier; 2015. p. 215-261.
See especially Chapter
3.09.4.1.2 Decadal variations and core-mantle interactions
(pp. 230-232, and Figure 4).
Richard writes in this chapter:
"The most important mechanism acting to cause decadal variations in LOD is core-mantle coupling. While it has been recognized for quite some time that the core is the only viable source of the large decadal LOD variations that are observed ..., it was not until 1988 that Jault et al. (1988) were able to model the core angular momentum (CAM) and show that it causes decadal LOD variations that agree reasonably well with those observed."
The reference is:
Jault D, Gire C, and Le Mouel J-L (1988) Westward drift, core motions and exchanges of angular momentum between core and mantle. Nature 333:353-356.
There are much more references in this chapter.
From Figure 4 it can be seen that a decrease in LOD was also observed between 1860 and 1870 and between 1915 and 1930. The models agree rather well with the observations, especially between 1900 and 1990. The chapter discusses also in length the mechanisms of core-mantle interactions. There are open questions: "While the exchange of CAM with the solid Earth can clearly cause decadal LOD variations of approximately the right amplitude and phase, the mechanism or mechanisms by which the angular momentum is exchanged between the core and solid Earth are less certain."
If you have problems to get these papers, I may help.
Best regards,
Wolfgang
15th Sep, 2015
Alfredo Oliveira
Dear Wolfgang
Thank you very much! I will see carefully the papers and I will give feedback.
My main interest is to know what is the influence of tidal effect on Earth rotation; because if one considers that the Moon-Earth tidal effect is the cause of the increase of Moon's orbit, than one has to explain not just the oscillations of Earth rotation but also why it is not slowing down has required to explain the increase of Moon's orbit.
My intuition about this is that we need to consider other phenomena, namely the presumed rising of oceans, which can be just an oscillation downwards of parts of the mantle where continents lay and upward oscillation of the parts dominated by oceans; or also a sinking of continents can be going on. Both situation can drive variations in rotation speed of the Earth and the order of magnitude of a sinking of continents (which would be around 3 mm/year) is not far of what is required to explain the acceleration of rotation. I don't think that just one phenomenon is the explanation but that there are two or three that are responsible for it; certainly the core-mantle coupling is one.
So far, I have not been able to reach an explanation compatible with the considered consequences on Earth rotation of the tidal effect of Moon and also Sun, which leads me to think that the order of magnitude of tidal effect may be lower then presumed; your contribution is very important for me because it will probably help me in determining how important can be the contribution of core-mantle coupling to compensate for tidal effect, i.e., to explain the oscillations plus the expected consequences of tidal effect
8th May, 2020
Cor Seinen
University Medical Center Utrecht
Hi Alfredo, Earth rotational speed is increasing when the solar activity is increasing this has to do with the dynamin pressure difference of the solar wind on the bow shock / magnetosheat . It has do do with the magnetic reconnection of the magnetic field of planet earth. You have to realize earth magnetic field is rotating and the solar wind creates small ripples upstream of the bow shock when the angle of the solar wind in respect to earth magentic field is changing there are more breaches in the magnetic field. Downstream the bow shock the ripples are bigger and pockets in the magnetic field are forming. The solar wind gets some kind of trapped in these pockets and the dynamic solar wind pressure increases locally dramatically. this gives a netto pressure solar winds difference on the earth magnetic field. Because of magnetic field line reconnection on the night side earth magnetic field becomes smooth again. This process gives earth a rotonial drive eastwards and contributes to the spin.
8th May, 2020
Alfredo Oliveira
Thank you Cor Seinen. That is very interesting, and I did not thougth on it. However, the acceleration I mention is a four decades long aceleration, and solar activity has increased and decreased meanwhile, so I thing that the explanation may be geological. Anyhow, what you said is an interesting contribution to the variations of Earth rotation, one that is new to me
10th May, 2020
Alfredo Oliveira
Cor Seinen I noticed that indeed it seems that there is a correspondence between the variation of Earth rotation and solar activity; however, it is the opposite of what you said - earth rotation is accelerating since solar activity is decreasing. Maybe your theory is correct but the effect is the opposite, i.e., solar wind opposes to the rotation of Earth's magnetic field. On the other hand, this may be the cause of the inversions of the magnetic field, which, in this case, could be due to some superflare that hit Earth. What do you think?
13th May, 2020
Cor Seinen
University Medical Center Utrecht
Hi Alfredo.
Maybe there is some debate with respect to LOD in relation to solar activity I found several articles pointing in the direction LOD decrease with increasing of solar activity.
Title of LOD articles: Measurement of the Earth’s
rotation: 720 BC to AD 2015
both article found a inverse correlation of LOD and solar intensity on a larger time scale.
The first article superimposed the seasonal variation of solar activtiy on a larger time scale.
But maybe you have found other articles?
For as I understood now: The rotational forces in the fluid outer core of earth (westward drift) is a negative regulator on the rotational speed of earth.
The tidal friction of the moon is also a negative regulator of the rotational speed of earth.
Let's Imagine (thougt experimen): If you have a solid rotating spere in a continuous stream of air. Then the pressure of the wind is higher at one side of the sphere (the side that's rotate towards the wind stream) the pressure of the wind stream is lower at the side of the sphere that is rotating away from the wind stream. So there is a pressure difference at both side of the sphere and eventually the sphere stops rotating (because of the continous windstream).
Now let's take the rotating magnetic field of planet earth and the continous solar plasma stream towards this rotating magnetic field. If the magnetic field is not breached, rippled of have local pockets because of the solar plasma then the solar wind should also be a negative regulator in respect to the rotational speed of the earth, because a solar plasma pressure difference is working against the rotation of earth's magnetic field. To summerize: if the solar activity, the tidal friction of the moon and the westward drift (rotaional forces) of the outer liquid core of planet earth are all negative regulators in respect of the rotational speed. what is keeping the earth spinning for thousend of years? Especially those period's that earth's rotation is speeding up.
So that's why I think that because of the breaces, ripples and formed pockets in the magnetosheat of earth's magnetic field downstream of the bowshock, the solar plasma gives a netto positive momentum on the rotating magentic field of planet earth, and thereby is a positive regulator in relation to the rotational speed of planet earth, but I am still investigating it is a very interdiscpine field of research.
Mabye the geodynamic engine of planet earth is some kind of a positive regulator in relation of the rotational speed of planet earth. Because the rotation of the metal (iron nickle) ions (positively charged) should rotating eastwards around the magnetic field lines of planet earth. This will create liquid convection streams of liquid metal in the outer core rotating eastward. And this eastwards directed convection streams of liquid metal in the outer core can maybe created a small eastward momentum in the westward drift of the liquid outer core. The electrons (current) should rotating westwards around the magnetic fied lines.
I do research in respect to the expected grand solar minimum, as a consequnce I think the rotational speed decrease to some extend which has as result that planet earth is more spherical shaped and less elongated along the equator.
this (deformation) gives friction in the earthmantel and more geoactivity (volcanic eruptions and earthquakes and a expected decease of the earth's temperature.
Here is a nice article about the expected grand solar minimum
see article:
Oscillations of the baseline of solar magnetic field and solar irradiance on a millennial timescale
This article is retracted but I think that still a lot of information is valid. Especially the model of more magnetic fields in the sun in relation to expected decrease of solar activity.
if you found articles about the rotaional speed of planet earth I am very interesting.
13th May, 2020
Cor Seinen
University Medical Center Utrecht
Hi Alfredo,
Some additional info:
Article: Rotation of the Earth, solar activity and cosmic ray intensity
The article I mentioned above made graphs with inverted LOD. So please be aware of this.
Have a nice day.
2nd Mar, 2021
Paul Vaucher
University of Applied Sciences and Arts Western Switzerland
The overall phenomenon seems to be towards deceleration...

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