The question is in regards to the asymmetry of the changeover latitudes and NOT about why it needs to be changed.

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    $\begingroup$ Southern tip of South America is about 60S $\endgroup$ – expeditedescent Sep 6 '20 at 13:11
  • $\begingroup$ @expeditedescent I made that observation as well, but it doesn't seem like a consistent reason as the highest northern land mass extends to 83N. $\endgroup$ – Darshan Patil Sep 6 '20 at 13:40
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    $\begingroup$ Because there’s a lot more airports between 60N and 73N than between 60S and 73S? $\endgroup$ – StephenS Sep 7 '20 at 0:18
  • $\begingroup$ At 65°S, wouldn't the pole be on the wrong side for certain longitudes? (as the South pole is at 64°S lat.). $\endgroup$ – mins Sep 19 '20 at 3:01

Earth's magnetic field is not symmetric north to south. In particular, the magnetic declination can get significantly larger at a given southern latitude than it does at the corresponding northern latitude. This can be seen by looking at a world declination map:

enter image description here

Curves of a given declination reach much lower southern latitudes than they do northern latitudes. For example, the highlighted curve is 40° west of north declination; its southernmost point in the northern hemisphere is at about 75°N, but its northernmost point in the southern hemisphere is at 35°S (!). Another way this manifests is that the South Magnetic Pole is at a significantly lower latitude than the North Magnetic Pole (~65°S vs. ~85°N).

As to why the Earth's magnetic field is so asymmetric, that's a question for Earth Science.SE. My understanding is that you may not get a good answer over there either; the behavior of Earth's magnetic field is complex and not fully understood.


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