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Magnetic North  
User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Posted (16 years 1 month 4 days 11 hours ago) and read 1495 times:

Today I learned that the magnetic pole of the Earth drifts around over time, and so some runways periodically get renamed (i.e., was 27L, now 28L) because the compass reads differently than it did a few years ago. How many years does this drift pattern take to complete a cycle? Or is it a recurring cycle?


6 replies: All unread, jump to last
User currently offlineFr8tdog From United States of America, joined Feb 2000, 120 posts, RR: 0
Reply 1, posted (16 years 1 month 4 days 7 hours ago) and read 1390 times:

Runway numbers are changed as needed, I think the avg. is around 10-11yrs. this depends on the geographic location.

User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 2, posted (16 years 1 month 4 days 6 hours ago) and read 1387 times:

I believe the trend is about a degree every 50-60 years... depending on where you are located.If you have access to a nautical chart, it will have annual rate of change for that area inside each compass rose... I always tell people that the change will be insignificant in your lifetime, so don't worry about it... Apparently it takes several millenia for the magnetic poles to switch...

Scientist have studied iron deposits around the earth in different stratas of the crust, and have indeed found evidence that this has been a recurring trend.

I believe the current trend is the pole is moving underneath the general area of 90W in a northerly direction right now.... at about 15 kilometers per year.

Some people instinctively feel that this movement is a "bad" thing, but it certainly is not... the magnetic compass is fast becoming a relic of the past... It is my opinion that runways should should be renamed to true headings as soon as WAAS is implemented....

User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 3, posted (16 years 1 month 3 days 21 hours ago) and read 1374 times:

So the movement is towards the south pole? I had pictured it as a circular pattern somewhere up north. Interesting. I wonder why it is moving?

User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 4, posted (16 years 1 month 3 days 19 hours ago) and read 1372 times:

I explicitly said in my previous message that the current trend is northerly movement.

However, it will one day reach it's apogee and begin moving south again...

look at this picture again:

it is moving almost due north underneath canada right now....

I also first believed that it moved in a line following something that looks like the arctic circle, but then I was proved wrong, so I accepted the obvious...

flow of eltrical currents in the earth's core is to blame...

check out:


User currently offlineSamurai 777 From Canada, joined Jan 2000, 2461 posts, RR: 4
Reply 5, posted (16 years 1 month 3 days 19 hours ago) and read 1372 times:

The shifting of the magnetic poles are indeed caused by electrical currents running throuh Earth's outer core and lower mantle. These currents fluctuate probably due to the sloshing of the mantle.

A potentially serious concern, especially for aircraft navigation systems, is that we are overdue for another magnetic field reversal(in terms of strength and direction of current), as the magnetic field has been switching every 700,000 years for last 2-3 million years. There is an awful lot of evidence of reversals, especially in volcanic rocks, which contain iron deposits.

Currently, the north magnetic pole is stronger than the south magnetic pole(sitting in Antarctica). A reversal would be a problem because during that time, the magnetic field is temporarily weakened greatly and compasses or navigational aids that rely on compasses would be rendered useless worldwide. Aircraft, both commercial and military, rely on navigation systems greatly. This will be a problem, unless a greater emphasis is placed on satellite navigation systems, like the GPS. The GPS(Global Positioning System) is a network of at least 22 satellites currently in orbit worldwide. If a commercial aircraft used this, only 3 or 4 satellites are used to triangulate the position, which is accurate within 100 metres(330 ft). The military version is about 10 times more accurate.

Also, with the magnetic field weakened during a reversal, there is the concern of greater exposure to cosmic radiation and charged particles from the sun at higher altitudes, not only to astronauts, but also pilots and passengers who fly frequently enough. Although the greater exposure wouldn't be that deadly, cancer is more of a problem. Even now, the region around the North Magnetic pole is a concern to such people on polar routes, because there is less of the magnetic field protecting Earth from the cosmic radiation.

A reversal would probably take about a century or perhaps over a thousand years, but little is known about them, as a reversal has never happened in recorded history.

User currently offlineBigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0
Reply 6, posted (16 years 1 month 3 days 14 hours ago) and read 1366 times:

Sorry. When I first read Aaron's post I got hung up on the words "it takes several millenia for the magnetic poles to switch", missing the word "northerly" in the later sentence.

Seems to me having the magnetic pole moving north to coincide with the north pole is a good thing. But as you all pointed out, it moves so slowly it really doesn't matter.


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