BigGiraffe From United States of America, joined Jan 2000, 257 posts, RR: 0 Posted (15 years 3 months 4 weeks 1 day 17 hours ago) and read 1415 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?
Aaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 2, posted (15 years 3 months 4 weeks 1 day 12 hours ago) and read 1307 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....
Samurai 777 From Canada, joined Jan 2000, 2461 posts, RR: 4
Reply 5, posted (15 years 3 months 4 weeks 1 day 1 hour ago) and read 1292 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.