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    Re: Magnetic variation changing faster than anticipated
    From: Frank Reed
    Date: 2019 Feb 24, 18:59 -0800

    Yes, this came up a few weeks ago, Mark. Here's something I wrote in mid-January: http://fer3.com/arc/m2.aspx/....g43933.

    And have a look in these maps. Notice that there's no real change in motion if you look at the north magnetic poles position every five years in the past twenty years or so. Also worth noticing is that the south magnetic pole is doing something completely different. The "actual" magnetic poles are determined by tiny differences in horizontal field strength. Tracking their exact motion has dubious value.



    The version of the story at maritime-executive.com is just poor science, science by press release (and the comments... wow! ...the loonies all came out).

    The speed of the north magnetic pole has barely changed since the beginning of the century. There are some issues here, yes, but they have no bearing on any practical navigation issues. The north magnetic pole did not "speed up" but it did defy some educated guesses that it would finally slow down. That's about it. For most mid-latitude navigators, there is no measurable effect.

    Note also that there is a coordinate effect at work here. The longitude of the magnetic north pole is changing rather rapidly right now because the pole is passing through very high geographic longitude. Even without changing its speed over the ground, its rate of change in longitude accelerated sharply a few years ago. This is, in fact, quite similar to the noticeable acceleration of the SHA of Polaris in recent years. In the 1750s Polaris was two degrees from the celestial pole. By 1944 that polar distance had fallen to one degree. Now it has decreased its distance to 39 minutes of arc. As it gets closer, it passes through meridians of SHA more quickly, creating the illusion that its position is changing more rapidly than other stars.

    I think that part of the reason this magnetic field story got picked up and spread so quickly is that some early versions of coverage blamed the inability to publish new magnetic models on the partial government shutdown here in the US. There were plenty of things that could be blamed on that giant waste of time, but not much here. There was no "risk to navigation" caused by the barely delayed dissemination of the new model. But the suggestion that there was some delay, no doubt, made the story easier to sell to editors.

    Frank Reed

       
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