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IFL Science's Earth's North Magnetic Pole Is Heading Towards Siberia – And Scientists Now Know Why explains that the motion of Earth's north magnetic pole can be understood as follows:

A new study, published this week in the journal Nature Geoscience, argues the changes could be explained by the to-ing and fro-ing between two magnetic "blobs" of molten material in the planet's interior, causing a titanic shift of its magnetic field.

See also The BBC's Scientists explain magnetic pole's wanderings.

Are these blobs sufficiently distinct to describe their locations somehow, perhaps with spherical coordinates like latitude, longitude and distance from the center from the Earth, or some cartesian scheme?

Where are they?

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    $\begingroup$ Those "blobs of molten" change to "lobes of negative magnetic flux" when consulting the paper. Sounds like a cool paper and a superficial pop science article. Will read later :-) $\endgroup$ – user20217 May 7 '20 at 8:18
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    $\begingroup$ I tried reading the article but that's beyond my very limited knowledge of core geophysics and magnetism $\endgroup$ – Gimelist May 7 '20 at 12:16
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    $\begingroup$ I promised to read but don't have enough time right now, sorry. Though it's interesting ! $\endgroup$ – user20217 May 8 '20 at 9:02
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    $\begingroup$ @uhoh the tag convection might be added,i think it fits what is going on deep down in our planet. $\endgroup$ – trond hansen May 25 '20 at 5:07
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    $\begingroup$ @trondhansen that sounds good, thanks! You are welcome to edit my post and add it if you like, it adds a tiny amount to your SE reputation stuff. If not, then I'll add it. $\endgroup$ – uhoh May 25 '20 at 5:09
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The "blobs" referred to in the IFLS article are, more correctly, areas of strong magnetic flux at the Earth's surface. The term "blob" is not scientifically significant, it just refers to a region where the magnetic field coming from Earth's core is stronger than elsewhere. Often we'd depict the magnetic field with a contour map of field strength, giving peaks and troughs of strong and weak field the appearance of "blobs" or patches, like this summary image from the publication in question:

Radial magnetic flux at Earth's surface. Copyright P. Livermore, from ESA http://www.esa.int/Applications/Observing_the_Earth/Swarm/Magnetic_north_and_the_elongating_blob (source: P. Livermore, via ESA: http://www.esa.int/Applications/Observing_the_Earth/Swarm/Magnetic_north_and_the_elongating_blob)

The maps show the radial magnetic field strength at Earth's surface in 1999, and then the field in 2019, this time with a trail showing the movement of the North magnetic dip pole (the star) since 1999. The two "blobs" of stronger field can be seen to change, the one over Siberia gets bigger and pulls the pole towards it, away from the now smaller Canadian one.

These "blobs" of strong field on the maps aren't "molten material in Earth's interior", but we can infer from maps like this what the field would look like at the surface of the outer core, and then from there what the movement of the material within the outer core might have been in order to generate the magnetic field we've observed. This is thanks to (math heavy :( ) frozen-flux theorem, that essentially says magnetic field is "frozen" into the iron-rich fluid at the surface of the Earth's outer core, so acts like a tracer for the fluid movement at the top of the outer core.

For an idea of what the flow (labelled "|U|") of material at the surface of the core might look like during the last 20 years to produce the field (labelled "Br", note the flipped color scheme), here are stills from the same model cited by the publication's authors of the field and flow at the core surface in 1999 and 2017. The Canadian "blob" gets stretched out and weaker relative to a strengthening Siberian "blob", as the flow speeds up under Canada:

Magnetic field and flow at the core surface 1999Magnetic field and flow at the core surface 2017 (Source: https://geodyn.univ-grenoble-alpes.fr/, play with the great visualisations, but the animations are enormous files!)

So yes, you can map the distinct location of these "blobs" of strong field (though only outside the core), but bear in mind the maps are plotted with largely irrelevant choices of contour levels -- the field is continuous and varies smoothly, it's been drawn like this to highlight the "blobs" more clearly.

(Edit: added images of field and flow at the core surface to clarify, and make this answer a bit long...)

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  • $\begingroup$ I'm not convinced. The abstract speaks of "...two large-scale lobes of negative magnetic flux on the core–mantle boundary under Canada and Siberia." and "...elongation of the Canadian lobe, probably caused by an alteration in the pattern of core flow between 1970 and 1999" so I think we're talking about the field about 3000 km below the surface and some "blobs" at least in the flow pattern if not actual distinct structures. $\endgroup$ – uhoh May 25 '20 at 17:23
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    $\begingroup$ The quoted "large scale lobes of negative magnetic flux on the core-mantle boundary" are those shown in the maps at Earth's surface, for which I could find a nice summary plot showing the before and after.Downward continuation of the magnetic field from the Earth's surface to the core-mantle boundary (i.e. the surface of the outer core) is not a direct mapping, it's a filtering in time and space $\endgroup$ – WJB May 25 '20 at 17:27
  • $\begingroup$ Ya all we have as data are field measurements at the surface, but of course the field is produced thousands of miles below the surface, so the measured surface deviations are only hints of what's really going on in the molten electrically conductive layer(s). I do think there are blobs of molten material whose flow pattern produce strong effects in magnetic field at the core-mantle boundary, looks like I'll have to go read the paper to be certain though. $\endgroup$ – uhoh May 25 '20 at 17:33
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    $\begingroup$ Yes, the flow of material in the outer core generates the field, and as the flow changes, so does the resulting field. It's not blobs of core material moving as such - the core material is always moving - but the flow accelerates and decelerates, and the pattern of flow slowly changes. The authors think the flow under the Arctic changed over the last few decades, and the result was to move and stretch the patches of strong field being generated. $\endgroup$ – WJB May 25 '20 at 17:46

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