<p>The answer is that there are more forces than just the momentum of the earth at play. The electromagnetic force generated by the core is pushing on itself, in fact:</p>

<blockquote>
  <p>"The fact that Earth's internal magnetic field changes slowly, over a timescale of decades, means that the electromagnetic force responsible for pushing the inner and outer cores will itself change over time. This may explain fluctuations in the predominantly eastwards rotation of the inner core, a phenomenon reported for the last 50 years by Tkalčić et al. in a recent study published in Nature Geoscience."</p>
</blockquote>

<p>from <a href="http://www.sciencedaily.com/releases/2013/09/130916162005.htm" rel="noreferrer">http://www.sciencedaily.com/releases/2013/09/130916162005.htm</a></p>

<p>You see, these changes in the internal portions in the Earth's magnetic field cause a shear.  The Earth's magnetic poles are not stationary, they wander. There is clear evidence of this from the paleomagnetic record. This is caused by the viscous convection of the iron nickel outer core. Their numerical models showed that the electromagnetic torque :
<img src="https://i.sstatic.net/uznwp.gif" alt="enter image description here"> from P.W. Livermore et al. 2013</p>

<p>On the outer core has a westward direction, while the inner core's torque scales accordingly in the opposite direction. </p>

<p><img src="https://i.sstatic.net/rsXl8.gif" alt="">
 from P.W. Livermore et al. 2013</p>

<p>Finally a cross section (image above) of the asymmetric flow (off dipole) clearly shows opposite direction in the outer core and inner core (blue vs red on the color bar).</p>

<p>So, in summary:</p>

<ol>
<li>The electromagnetic field is modeled as a dipole, but in actuality has ~10% component that is off the dipole.</li>
<li>The wandering of this dipole (and by consequence, off dipole) magnetic field causes a shear in opposite directions at the inner and outer core.</li>
<li>This inner and outer core shear scales similarly at the edges (at the inner core outer boundary and at the core mantle boundary) but in opposite directions (so they are of the same magnitude).</li>
<li>This torque, causes the flow of the inner core and the outer core to spin in opposite directions, as shown by the last figure.</li>
</ol>

<p>This is a complex article, let me know if there is anything I could explain better. I think I've got this right. </p>

CC BY-SA 3.0
2014-04-22T04:42:24.650Z
2014-04-22T04:42:24.650Z
Neo
<p>The earth's core may rotate at a faster rate, not in the opposite direction, this would be consistent with heavier elements sinking to form the core during planetary differentiation. Conservation of angular momentum could cause it to rotate faster. See this question in Physics SE.</p>

<p><a href="https://physics.stackexchange.com/questions/68677/what-is-the-evidence-for-the-super-rotation-of-earths-inner-core">What is the evidence for the super-rotation of the earth's core?</a></p>

CC BY-SA 3.0
2014-04-22T03:05:47.100Z
Mark, the inner core rotates at a faster rate, but I believe the outercore actually rotates in the opposite direction to the superrotating inner core.
Kenshin
CC BY-SA 3.0
2014-04-22T03:39:04.957Z
sciencedaily.com/releases/2013/09/130916162005.htm
Kenshin
CC BY-SA 3.0
2014-04-22T03:41:57.127Z
doesn't that linked article provide the answer, geodude?
Neo
CC BY-SA 3.0
2014-04-22T03:45:37.990Z
Mark, that answer would be correct in a closed system, but there are external forces, the magnetic field of the earth pushing on both the inner core and outer core. The core behaves like an electro magnetic, with the liquid outercore its coil.
Neo
CC BY-SA 3.0
2014-04-22T03:45:41.740Z
Interesting reference thanks. They are proposing an electromagnetic mechanism which could do that. So it is emergent from their computer model?
Mark Rovetta
CC BY-SA 3.0
2014-04-22T03:58:46.717Z
Yes, this paper: http://www.pnas.org/content/110/40/15914 is the actual journal article science daily references.
Neo
CC BY-SA 3.0
2014-04-22T03:58:48.297Z
@Geodude you should post an answer citing that reference and explaining it so we can up-vote it. I'm not sure how long comments persist.
Mark Rovetta
CC BY-SA 3.0
2014-04-22T04:02:01.977Z
@MarkRovetta, I will spend some time looking through it, but I think it might be a bit too complex for me. Hopefully an expert will be able to shed some light.
Kenshin
CC BY-SA 3.0
2014-04-22T04:02:54.197Z
@Neo, are you able to post an answer explaining that complex paper?
Kenshin
CC BY-SA 3.0
2014-04-22T04:34:16.793Z
Yes, you should cite the PNAS paper since it appears to be the primary source and the full text is online.
Mark Rovetta
CC BY-SA 3.0
2014-04-22T03:00:52.027Z
2014-04-22T03:00:52.027Z
2017-04-13T12:40:15.470Z
Mark Rovetta
<blockquote>
  <p>Is it true that Earth's outercore rotates in the opposite direction to Earth's inner-core?</p>
</blockquote>

<p>No. You misread a badly written for-the-masses science article. The article summary is at best rather confusing and misleading. It invites a reader to misinterpret what's going on.</p>

<p>So what's really going on? It's simple, conceptually. The mantle, outer core, and inner core all rotate in more or less the same direction and at more or less the same rate. However, because outer core is liquid, there exists a possibility for the mantle, outer core, and inner core to exhibit slightly different rotation rates (and perhaps even rotation axes). That's apparently what is happening inside the Earth. The mantle and crust make one rotation per sidereal day. The inner core currently rotates a tiny, tiny bit faster than that, while the outer core rotates a tiny, tiny bit slower than that.</p>

<p>This means that when viewed from the perspective of an Earth-fixed observer, the outer core currently appears to be rotating a tiny, tiny bit westward and the inner core currently appears to be rotating a tiny, tiny bit eastward. It's a matter of perhaps confusing perspective. When viewed from an inertial perspective, the mantle, outer core, and inner core are all rotating more or less synchronously.</p>

<p><br>
When you read one of those science-for-the-masses type articles, it's a good idea to jump to the underlying journal article. In this case, you should try reading <a href="http://www.pnas.org/content/110/40/15914.long">Livermore, Hollerbach, and Jackson, "Electromagnetically driven westward drift and inner-core superrotation in Earth’s core", PNAS 110:40 (2013)</a>.</p>

CC BY-SA 3.0
2014-05-03T23:18:30.267Z
2014-05-03T23:18:30.267Z
David Hammen
<p>Is it true that Earth's outercore rotates in the opposite direction to Earth's inner-core?  Is there a plausible explanation for why this phenomenon occurs and what is the available evidence supporting this notion?</p>

CC BY-SA 3.0
2016-08-13T22:45:17.027Z
@Geodude -- This came up as a linked question. The answer depends on perspective. From the perspective of an inertial frame (one in which the mantle makes one rotation per day), the mantle, outer core, and inner core all rotate at almost the same rate, with the outer core rotating slightly slower and the inner core rotating slightly faster than the mantle. From the perspective of a frame rotating with the mantle, the outer core and inner core rotate in opposite directions.
David Hammen
CC BY-SA 3.0
2014-04-22T03:06:15.360Z
Can you please provide a link to a claim that the rotation is opposite?
naught101
CC BY-SA 3.0
2014-04-22T03:09:13.247Z
@naught101, http://www.sciencedaily.com/releases/2013/09/130916162005.htm, it says in summary section "while the outer core, comprising mainly molten iron, spins westwards at a slower pace."
Kenshin
CC BY-SA 3.0
2014-04-22T13:08:55.347Z
@Geodude I would add that reference to the question.
gerrit
<geophysics><geodynamics><core>
Why does Earth's outer-core rotate in the opposite direction to the inner-core?
Kenshin
# Why does Earth's outer-core rotate in the opposite direction to the inner-core?

(Asked by: username_0 on 2014-04-22)

Is it true that Earth's outercore rotates in the opposite direction to Earth's inner-core? Is there a plausible explanation for why this phenomenon occurs and what is the available evidence supporting this notion?

**Tags:** geophysics, geodynamics, core

> **Comments:**
> **username_2**: Can you please provide a link to a claim that the rotation is opposite?  
> **username_0**: @username_2, http://www.sciencedaily.com/releases/2013/09/130916162005.htm, it says in summary section "while the outer core, comprising mainly molten iron, spins westwards at a slower pace."  
> **username_3**: @Geodude I would add that reference to the question.  
> **username_1**: @Geodude -- This came up as a linked question. The answer depends on perspective. From the perspective of an inertial frame (one in which the mantle makes one rotation per day), the mantle, outer core, and inner core all rotate at almost the same rate, with the outer core rotating slightly slower and the inner core rotating slightly faster than the mantle. From the perspective of a frame rotating with the mantle, the outer core and inner core rotate in opposite directions.  

---

## 3 answers

### Answer by username_1 on 2014-05-03. Score: 15 | Accepted answer

> Is it true that Earth's outercore rotates in the opposite direction to Earth's inner-core?

No. You misread a badly written for-the-masses science article. The article summary is at best rather confusing and misleading. It invites a reader to misinterpret what's going on.

So what's really going on? It's simple, conceptually. The mantle, outer core, and inner core all rotate in more or less the same direction and at more or less the same rate. However, because outer core is liquid, there exists a possibility for the mantle, outer core, and inner core to exhibit slightly different rotation rates (and perhaps even rotation axes). That's apparently what is happening inside the Earth. The mantle and crust make one rotation per sidereal day. The inner core currently rotates a tiny, tiny bit faster than that, while the outer core rotates a tiny, tiny bit slower than that.

This means that when viewed from the perspective of an Earth-fixed observer, the outer core currently appears to be rotating a tiny, tiny bit westward and the inner core currently appears to be rotating a tiny, tiny bit eastward. It's a matter of perhaps confusing perspective. When viewed from an inertial perspective, the mantle, outer core, and inner core are all rotating more or less synchronously.

When you read one of those science-for-the-masses type articles, it's a good idea to jump to the underlying journal article. In this case, you should try reading [Livermore, Hollerbach, and Jackson, "Electromagnetically driven westward drift and inner-core superrotation in Earth’s core", PNAS 110:40 (2013)](http://www.pnas.org/content/110/40/15914.long).


---

### Answer by username_4 on 2014-04-22. Score: 8

The answer is that there are more forces than just the momentum of the earth at play. The electromagnetic force generated by the core is pushing on itself, in fact:

> "The fact that Earth's internal magnetic field changes slowly, over a timescale of decades, means that the electromagnetic force responsible for pushing the inner and outer cores will itself change over time. This may explain fluctuations in the predominantly eastwards rotation of the inner core, a phenomenon reported for the last 50 years by Tkalčić et al. in a recent study published in Nature Geoscience."

from <http://www.sciencedaily.com/releases/2013/09/130916162005.htm>

You see, these changes in the internal portions in the Earth's magnetic field cause a shear. The Earth's magnetic poles are not stationary, they wander. There is clear evidence of this from the paleomagnetic record. This is caused by the viscous convection of the iron nickel outer core. Their numerical models showed that the electromagnetic torque :
![enter image description here](https://i.sstatic.net/uznwp.gif) from P.W. Livermore et al. 2013

On the outer core has a westward direction, while the inner core's torque scales accordingly in the opposite direction.

![](https://i.sstatic.net/rsXl8.gif)
from P.W. Livermore et al. 2013

Finally a cross section (image above) of the asymmetric flow (off dipole) clearly shows opposite direction in the outer core and inner core (blue vs red on the color bar).

So, in summary:

1. The electromagnetic field is modeled as a dipole, but in actuality has ~10% component that is off the dipole.
2. The wandering of this dipole (and by consequence, off dipole) magnetic field causes a shear in opposite directions at the inner and outer core.
3. This inner and outer core shear scales similarly at the edges (at the inner core outer boundary and at the core mantle boundary) but in opposite directions (so they are of the same magnitude).
4. This torque, causes the flow of the inner core and the outer core to spin in opposite directions, as shown by the last figure.

This is a complex article, let me know if there is anything I could explain better. I think I've got this right.


---

### Answer by username_5 on 2014-04-22. Score: 4

The earth's core may rotate at a faster rate, not in the opposite direction, this would be consistent with heavier elements sinking to form the core during planetary differentiation. Conservation of angular momentum could cause it to rotate faster. See this question in Physics SE.

[What is the evidence for the super-rotation of the earth's core?](https://physics.stackexchange.com/questions/68677/what-is-the-evidence-for-the-super-rotation-of-earths-inner-core)

> **Comments:**
> **username_0**: Mark, the inner core rotates at a faster rate, but I believe the outercore actually rotates in the opposite direction to the superrotating inner core.  
> **username_0**: sciencedaily.com/releases/2013/09/130916162005.htm  
> **username_4**: doesn't that linked article provide the answer, geodude?  
> **username_4**: Mark, that answer would be correct in a closed system, but there are external forces, the magnetic field of the earth pushing on both the inner core and outer core. The core behaves like an electro magnetic, with the liquid outercore its coil.  
> **username_5**: Interesting reference thanks. They are proposing an electromagnetic mechanism which could do that. So it is emergent from their computer model?  
> **username_4**: Yes, this paper: http://www.pnas.org/content/110/40/15914 is the actual journal article science daily references.  
> **username_5**: @Geodude you should post an answer citing that reference and explaining it so we can up-vote it. I'm not sure how long comments persist.  
> **username_0**: @username_5, I will spend some time looking through it, but I think it might be a bit too complex for me. Hopefully an expert will be able to shed some light.  
> **username_0**: @username_4, are you able to post an answer explaining that complex paper?  
> **username_5**: Yes, you should cite the PNAS paper since it appears to be the primary source and the full text is online.  

---

