Viewing a single comment thread. View all comments

CrustalTrudger t1_j4w5c3v wrote

Reply to comment by Weed_O_Whirler in Why is it that the cardinal directions are perpendicular? by [deleted]

To add an extra level to the rabbit hole, there are actually three norths. True north, magnetic dip north, and geomagnetic north. True north has been covered, but magnetic dip north is the location where the magnetic field is oriented vertically (so if you had a magnetic inclinometer, where it would point vertically) whereas geomagnetic north is the intersection of the surface of the Earth with the best fit dipole field. In detail, if the Earth's magnetic field was a true dipole (like a bar magnet) then the north and south dip poles (1) would be antipodal with respect to each other and (2) they would be equivalent to the geomagnetic poles (which are by definition antipodal), but neither of those tend to be true as the location of the dip poles migrate as part of secular variation.

23

dukesdj t1_j4w8w7y wrote

> magnetic dip north is the location where the magnetic field is oriented vertically

Presumably in general magnetic dip poles do not strictly need to some as a single pair and could come in any number of pairs? I am essentially thinking along the lines that there is no strict mechanism to enforce that only two such locations would exist in a general astrophysical dynamo (for example there are many locations with locally vertical field at the surface of the Sun).

5

CrustalTrudger t1_j4w9a5g wrote

I would assume so, but as far as I know on Earth, we tend to find two distinct dip poles roughly equivalent to a north and south pole (i.e., one with a +90 inclination and one with a -90 inclination). You might expect that during a geomagnetic reversal (which is often described as a weakening/temporary collapse of the dipole component and thus a relative strengthening of the higher order field components) you could have more than one pair of dip poles, maybe?

6