Magnetic North is Constantly Shifting

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The earth is surround by a magnetic field, protecting our world against cosmic radiation and charged particles.  Pull out a compass and watch as the needle points you towards north.  While other factors about the earth’s magnetic field also influence your compass, the direction the needle generally points towards is known as the Magnetic North Pole.   The location of the Magnetic North Pole is not constant and moves on both a daily and annual basis.

What is the Magnetic North Pole?

The location of the Magnetic North Pole is the spot on earth where if you stood with a compass, the needle would point directly down.  The inclination measurement for the magnetic field at this location is 90 degrees.

How is the Magnetic Pole Different from the Geographic North Pole?

The geographic North Pole is found where the lines of longitude converge at the latitude of 90 degrees North and is the end of the Earth’s axis. The direction towards the North Pole is referred to as true (or due) north and the angular difference between the North Pole and the MNP is known as the magnetic declination. The line along the earth where there is no difference between the Magnetic North Pole and the Geographic North Pole is known as the agonic line.

Early Efforts to Find the Magnetic North Pole

While the first compasses were in use in China as early as the first century, it was during the twelfth century that compasses became an important tool for navigation in Europe.  As those navigators discovered that the direction the compass pointed towards was not the same as geographic north, cartographers tried to figure where the exact location of the Magnetic North Pole was.  In 1539, Swedish writer Olaus Magnus depicted the location of the MNP as “Insula Magnetu” (Latin for “Island of Magnets”) off modern day Murmansk in his map, Carta Marina. Gerhard Mercator, most noted for his creation of the mercator projection popularly used on many online mapping applications such as Google Maps, attempted to located the MNP in 1646 through the intersection of great circles created from the measurements of magnetic declination at various points on the earth .  It wasn’t until William Gilbert who wrote “de Magnete” in 1600 that the theory was introduced that it was not an island or external feature that pulled compass needles north, but rather a force within the center of the earth.

Mercator's 1606 map of the North Pole. Mercator believed the North Pole to be a large magnetic black rock, the Rupes Nigra. Mercator wrote to Englishman John Dee, "In the midst of the four countries is a Whirl-pool, into which there empty these four indrawing Seas which divide the North. And the water rushes round and descends into the Earth just as if one were pouring it through a filter funnel. It is four degrees wide on every side of the Pole, that is to say eight degrees altogether. Except that right under the Pole there lies a bare Rock in the midst of the Sea. Its circumference is almost 33 French miles, and it is all of magnetic Stone."

Mercator’s 1606 map of the North Pole. Mercator believed the North Pole to be a large magnetic black rock, the Rupes Nigra. Mercator wrote to Englishman John Dee, “In the midst of the four countries is a Whirl-pool, into which there empty these four indrawing Seas which divide the North. And the water rushes round and descends into the Earth just as if one were pouring it through a filter funnel. It is four degrees wide on every side of the Pole, that is to say eight degrees altogether. Except that right under the Pole there lies a bare Rock in the midst of the Sea. Its circumference is almost 33 French miles, and it is all of magnetic Stone.”

Find the Location of the North Magnetic Pole

It took until 1831 to finally find the exact location of the North Magnetic Pole. Magnetic observations performed by 1829 narrowed down the suspected area to an unexplored area of the central Arctic.  An expedition to the west coast of Boothia Peninsula in Canada (70 degrees 05.3 minutes N, 96 degrees 46 minutes W) was led by James Clark Ross in May of 1831.  Ross located the spot where the magnetic inclination was 89 degrees 59 minutes. In 1904, Roald Amundsen measured the location of the MNP at 70 degrees 31 minutes N 96 degrees 34 minutes W.

Since then, Canadian scientists at Natural Resources Canada (NRCan) have conducted North Magnetic Pole surveys done in 1947, 1994, and 2001. Since it was first measured in 1831, the trend of migration for the MNP has been northward and seaward migrating 1,100 kilometers (about 683 miles).

Modelled (blue) and observed (red) locations of the Magnetic North Pole.

Modelled (blue) and observed (red) locations of the Magnetic North Pole.

Why Do the Magnetic Poles Move?

The magnetic poles shift each year due to changes in the Earth’s core in response to charge particles emitted by the sun hitting the earth’s magnetic field. The Earth’s core is made up of a solid iron center surrounding by a thick layer of liquid iron and nickel. The movement of this liquid metal creates the earth’s magnetic field.

Researchers at the Geological Survey of Canada measured the daily movements of the MNP using the CANadian Magnetic Observatory System (CANMOS) and found that the diurnal variation of its location is up to 80 kilometers with the average path of the variation forming an oval around a given point. Since measurements of the MNP began, its location has been slowly drifting over the Canadian Arctic towards Siberia in Russia.

When North Becomes South and South Becomes North

The polarity of the poles is another factor that is not constant. Known as geomagnetic reversal, this phenomenon occurs every 300,000 years on average (although the range in time between reversals varies from 100,000 years to tens of millions of years). Scientists are able to detect reversals of the magnetic poles by analyzing magnetic field information imprinted on rocks dating back 300 million years. The last flip in magnetic poles occurred about 780,000 years ago.

How Airports are Affected by Changes in the Shifting Magnetic North Pole

In order to help pilots land aircraft, airport runway numbers are actually based on magnetic compass direction.   Changes in the location of the Magnetic North Pole therefore have a major impact on runway designations and charting which rely upon geomagnetic information.  When the magnetic pole locations change more than three degrees, it can affect runway designations.  Runway locations are based on the constant force of the magnetic field because unlike satellite navigation, which can be subject to loss of availability, or visual navigation, which can be obstructed by snow or fog, the magnetic force is constant. Periodically, the shift in the Magnetic North Pole will trigger a need to renumber runways to reflect the new direction. For example, in January of 2011, Tampa Airport closed down its primary airway to renumber it from 18R/36L to 19R/1L to reflect the shift.

Scientists continue to study the earth’s magnetic field in order to better understand the wanderings of the Magnetic North Pole.  The Magnetic North Pole continues its migration and is predicted to eventually cross in Russia from Canada.

References

Edwards, Lin. “Tampa Airport Runways Renumbered Due to Magnetic North Movement.” Tampa Airport Runways Renumbered Due to Magnetic North Movement. Phys.org, 10 Jan. 2011. Web. 03 Jan. 2014.

“Geomagnetism – North Magnetic Pole.” Http://www.nrcan.gc.ca/. Natural Resources Canada, 31 Dec. 2005. Web. 3 Jan. 2014. https://web.archive.org/web/20060304124134/http://gsc.nrcan.gc.ca/geomag/nmp/northpole_e.php .

Mandea, M. and E. Dormy, “Asymmetric behavior of magnetic dip poles“, Earth Planets Space, 55, 153–157, 2003.

Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996). “Chapter 8”. The magnetic field of the earth: paleomagnetism, the core, and the deep mantle. Academic Press. ISBN 978-0-12-491246-5.

National Geophysical Data Center, “Wandering of the Geomagnetic Poles

Newitt et al., “Location of the North Magnetic Pole in April 2007“, Earth Planets Space, 61, 703–710, 2009

Phillips, Tony. “Earth’s Inconstant Magnetic Field.” NASA.gov. NASA, 29 Dec. 2003. Web. 03 Jan. 2014. http://www.nasa.gov/vision/earth/lookingatearth/29dec_magneticfield.html.

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