Inner core super-rotation

Inner core super-rotation is the eastward rotation of the inner core of Earth relative to its mantle, for a net rotation rate that is usually^{[clarification needed]} faster than Earth as a whole.

There are numerous conflicting schools of thought regarding the causes of a super-rotation. Earth's cooling vs dark energy conjectures are discussed in the detailed "Theory" portion herein.

A 1995 model of Earth's dynamo predicted super-rotations of up to 3 degrees per year; the following year, this prediction was supported by observed discrepancies in the time that p-waves take to travel through the inner and outer core. Utilizing both s and p waves dramatically increases the confidence levels of the many seismic data conclusions.

Seismic observations have made use of a direction dependence (anisotropy) of the speed of seismic waves in the inner core, as well as spatial variations in the speed. Other estimates come from free oscillations of Earth. The results are inconsistent and the existence of a super-rotation is still very controversial, but it is probably less than 0.1 degrees per year.

When geodynamo models take into account gravitational coupling between the inner core and mantle, it lowers the predicted super-rotation to as little as 1 degree per million years. For the inner core to rotate despite gravitational coupling, it must be able to change shape, which places constraints on its viscosity.

A 2023 study reported that the spin of the Earth's inner core has stopped spinning faster than the planet's surface around 2009 and likely is now rotating slower than it, which is possibly the result of mistaken eddy currents from opposing flows that led to this likely erroneous conclusion. ^[1]

^
Yang, Yi; Song, Xiaodong (February 2023). "Multidecadal variation of the Earth's inner-core rotation". Nature Geoscience. 16 (2): 182–187. Bibcode:2023NatGe..16..182Y. doi:10.1038/s41561-022-01112-z. ISSN 1752-0908. S2CID 256702306.
- News article about the study: "Earth's inner core seems to be slowing its spin". Washington Post. Archived from the original on 18 February 2023. Retrieved 16 February 2023.

[10.1038/s41561-022-01112-z-1] Yang, Yi; Song, Xiaodong (February 2023). "Multidecadal variation of the Earth's inner-core rotation". Nature Geoscience. 16 (2): 182–187. Bibcode:2023NatGe..16..182Y. doi:10.1038/s41561-022-01112-z. ISSN 1752-0908. S2CID 256702306.
News article about the study: "Earth's inner core seems to be slowing its spin". Washington Post. Archived from the original on 18 February 2023. Retrieved 16 February 2023.

[2] News article about the study: "Earth's inner core seems to be slowing its spin". Washington Post. Archived from the original on 18 February 2023. Retrieved 16 February 2023.

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