Some uncertainties with this topic. Researchers here propose a 70-year cycle, but other theories say 20-30 years, or even no cycle at all.
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Earth’s inner core, a hot iron ball the size of Pluto, has stopped spinning faster than the planet’s surface and might now be rotating slower than it, research suggested on Monday.
Roughly 5,000 kilometers (3,100 miles) below the surface we live on, this “planet within the planet” can spin independently because it floats in the liquid metal outer core, says Phys.org.
Exactly how the inner core rotates has been a matter of debate between scientists—and the latest research is expected to prove controversial.
What little is known about the inner core comes from measuring the tiny differences in seismic waves—created by earthquakes or sometimes nuclear explosions—as they pass through the middle of the Earth.
Seeking to track the inner core’s movements, new research published in the journal Nature Geoscience analyzed seismic waves from repeating earthquakes over the last six decades.
“We believe the inner core rotates, relative to the Earth’s surface, back and forth, like a swing,” the study’s authors, Xiaodong Song and Yi Yang of China’s Peking University, told AFP.
“One cycle of the swing is about seven decades,” the authors said.
The inner core started rotating slightly faster than the rest of the planet in the early 1970s, the study said.
But it had been slowing down before coming in sync with Earth’s rotation around 2009, it added.
There has been a “negative trend” since, the study said, meaning the inner core is now rotating slower than the surface.
The researchers predicted the next change would occur in the mid-2040s.
They said this rotation timeline roughly lines up with changes in what is called the “length of day”—small variations in the exact time it takes Earth to rotate on its axis.
Stuck in the middle
So far there is little to indicate that what the inner core does has much effect on surface dwellers.
But the researchers said they believed there were physical links between all Earth’s layers, from the inner core to the surface.
“We hope our study can motivate some researchers to build and test models which treat the whole Earth as an integrated dynamic system,” they said.
Experts not involved in the study expressed caution about its findings, pointing to several other theories and warning that many mysteries remain about the center of the Earth.
Full article here.
Tallbloke's Talkshop 
Umm wondering … if the core rotates more slowly does the surface rotate more quickly to compensate? LOD data, conservation of angular momentum, etc. Sol does it too?
I recall this was interesting: https://tallbloke.wordpress.com/2016/02/02/r-j-salvador-2016-prediction-for-changes-in-earths-length-of-day-lod/
[…] Earth’s inner core rotating slower than surface, study suggests […]
Interesting that the Earths core rotation changes that happened for the last two occurrences (1970 & 2009) lines up very well with the solar reversals of angular momentum. Perhaps we are seeing the first evidence of spin orbit coupling??
So the core oscillates like a washing machine agitator?
Hmmm.
Also in 1967-70 and 2005-09 the Jupiter-Sun line stuck close to the SS barycentre for an extended period.
The barycenter is a purely mathematical construct. Nothing physical there. A barycenter of a donut is in the hole.
The cycle is the thing. Repeats at ~179-year intervals can be seen on the solar simulator. There may be two overlapping 179-year cycles going on, the second nearly forty years (2 Jupiter-Saturn conjunctions) after the first.
See here — https://tallbloke.wordpress.com/2016/12/01/gerry-pease-links-improved-and-updated-solar-planetary-paper/
A solid core? So Al Gore’s million degree core doesn’t apply? [/sarc]
When I read about the rotation, I started to think about a dynamo.
Something else popped up in my mind – magnetic pole shift.
The BBC version of all this has the spin changing direction, but the one we’ve used calls itself an update. The footnote says their original version wrongly spoke of a direction change.
BBC version — https://www.bbc.co.uk/newsround/64388435.amp
Phys.org: ‘Correction note (January 25, 2023): Corrects throughout story dated January 23 to say that core’s rotation has slowed compared to Earth’s surface, not changed direction.’
Reblogged this on Climate Collections.
@JB – I love your simple common sense analogy. In the 60’s my parents bought me a birthday present of a self-winding Accurist watch, a super slim “sundial” or some similar name (can’t recall exactly). Loved it! Inside it had this oscillating weight for winding the main spring while you were wearing it. Kept really good time unless you got near a magnet and the hair spring (balance spring) would magnetise. The watch would then speed up 5 minutes a day. It was easily fixed by the jeweller degaussing it. LOD has been falling for some years now and Earth is rotating faster (International Earth Rotation and Reference Systems). It ought to be rotating a few seconds per century slower, on average. I am not saying the Earth’s hairspring may have been magnetised but if there is an analogy with my watch, scientists should “watch” out to avoid jumping to “silly science” conclusions!
“LOD has been falling for some years now and Earth is rotating faster (International Earth Rotation and Reference Systems)”
An increase in angular velocity indicating a decrease in polar moment of inertia, such as would be caused by a redistribution of mass from the Equator to the poles caused by a gain in mass of the Antarctic and Greenland ice caps?
I have wondered for some time whether LOD anomalies can be considered as a proxy for polar land ice mass variation.
catweazle. I also thought there might be a tell-tale here. The problem I have is surface water is just 0.02 percent of Earth’s mass and accumulation of ice near poles just presses down on crust and squirts mass elsewhere. Now the alleged iron core is subject to eddies from electromagnetic stuff and maybe a bit of planetary gravity agitation. How else can we explain such slow cooling of the core? I see some of the planetary stuff in LOD but clock-work does not explain it all.
Peter, there is a question of orders of magnitude, the leap second is a very small fraction of the time period involved, so it wouldn’t require much alteration of the polar moment of inertia caused by the redistribution of mass to account for the very small increase in angular velocity.
As to the cooling of the core, I believe much of the heating is caused by radioactive decay of the fissionable isotopes, how much that may be reducing over time I wouldn’t know.