[SFDXA] The wandering magnetic pole

[Bill]

 From Tony N2MFT"


  The wandering magnetic pole


          Compass needles point to a wandering magnetic pole


  April 30, 2019
  Lenox Grasso <https://www.oceannavigator.com/author/lenox-grasso/>
  Pole1In the Northern Hemisphere, magnetic variation is the angle
  between the Geographic (true) North Pole and the North Magnetic Pole.

  The Earth’s Magnetic North Pole, where the lines of magnetic force
  enter the Earth perpendicular to the globe’s surface, is actually a
  wandering location. Computer modeling of satellite data has it passing
  in 2018 closer to the Geographic North Pole than at any other time in
  its recorded history. What does the movement of this magnetic
  reference point mean for navigators using magnetic compasses?

  English philosopher William Gilbert first calculated the existence of
  the Magnetic North Pole in 1590 (published in 1600). Since then,
  through 1831, when British Naval Officer James Clark Ross became the
  first to reach it physically, and up until 1898, the Magnetic North
  Pole has meandered aimlessly through the islands and waterways of
  northern Canada. But since 1898, it has been moving steadily
  north-northwestward. At the beginning of the 20th century, it advanced
  about five miles each year. Then in 1970, it began to move faster.
  Today, the Magnetic North Pole moves about 25 miles each year. Soon,
  it will be at 86.471° N and 178.755° W, a distance less than 212
  nautical miles away from the Geographic North Pole. By 2019, the
  Magnetic North Pole will have traveled across the International Date
  Line, into the Eastern Hemisphere, and will be falling away from true
  north toward Siberia.

  The reason we, as mariners and navigators, are interested in this is
  because of magnetic variation and its effect upon our ship’s compass.
  Variation, the “V” in the “add East < T | V | M | D | C > add West”
  formula, is a force outside our boat stemming from our position on the
  Earth’s surface. It is the angular difference between our geographic
  and magnetic meridians, expressed in degrees east or west. More
  simply, it is the difference in degrees between what our compass
  “feels” as magnetic north versus true north. For sailors on the East
  Coast of the U.S., the variation in the compass roses on nautical
  charts is west. On the West Coast, variation is east. For sailors on
  western Lake Superior and along the Gulf Coast off New Orleans, there
  is no variation. Boats on these waters are on an agonic line where
  magnetic north and true north just happen to line up on the same
  geographic meridian.

  There are actually eight north poles. This discussion disregards five
  of them: the Instantaneous North Pole, the Celestial North Pole, the
  North Pole of Balance, the North Pole of Inaccessibility and North
  Pole, Alaska. The last is a suburb of Fairbanks far from the other
  north poles, but it is the one important to American children at
  Christmas. We care about these three: the Geographic North Pole, the
  Magnetic North Pole and the Geomagnetic North Pole.

  *The Geographic North Pole*
  This is true north, the northernmost point of the Earth as determined
  by the northern tip of its imaginary rotational axis. It is a mostly
  fixed point, subject to only 30 feet of wobble every 433 days. This is
  the top of the world, 90 degrees north latitude. All the great circle
  meridian lines of longitude converge here, as do all of the world time
  zones. Standing (or floating) at this spot, north, east and west no
  longer exist! The only way that explorers who vanquish these three
  compass cardinal points can leave the Geographic North Pole is to step
  south. It does not matter which way to step; in every direction, the
  only direction is south.

  Tracking the changing position for the North Magnetic Pole.

  *The Magnetic North Pole*
  The northern end of a magnetized compass needle frequently points
  here. It is not located at the Geographic North Pole, but it’s close
  enough to be useful in navigation. The reason it moves about 25 miles
  each year is due to earthquakes, electrical fluctuations in the Van
  Allen radiation belts, the ionosphere and the magnetosphere, but it is
  mostly due to our planet’s internal physical structure. Earth’s
  magnetic field originates in its core. The inner core is probably
  solid iron. Surrounding the solid inner core is a molten outer core of
  liquid metal alloys, mostly iron and nickel, that lies about 1,900
  miles beneath our feet. Next out is the mantle that is solid but
  malleable, and then what we see every day, land and sea, is the crust.
  As the Earth rotates on its axis, the inner and outer cores rotate
  too, but each at a different rate, which creates a geodynamo effect.
  Immense heat from the inner core — hotter than the surface of the sun
  — caused by radioactive decay and the conversion of potential energy
  in heavy metals sinking down to the inner core, drives the motion of
  the liquid metals in the outer core. Convection currents of moving
  molten metals generate electrical currents that produce the Earth’s
  magnetic field. And because the source of the Earth’s magnetic field
  is moving, the Magnetic North and South Poles move as well. If the
  Earth’s magnetic field were generated by a large, powerful, solid,
  dipole (two poles) bar magnet within the solid inner core, instead of
  by moving molten metal alloys in the liquid outer core, the Magnetic
  North and South Poles would remain mostly static.

  Anyway, Earth’s magnetic field emerges from the outer core vertically
  at the Magnetic South Pole, extends out into space and re-enters
  perpendicularly at the Magnetic North Pole. A compass needle dips
  there, trying to point straight down. Accordingly, this pole’s
  alternate name is the magnetic dip pole, not to be confused with
  dipole. At the Magnetic South Pole, a compass needle jumps upward. I
  was there once by boat — the Magnetic South Pole has been off the
  coast of Antarctica since 1962 — and a compass needle really does try
  to point skyward!

  *The Geomagnetic North Pole*
  The electrical currents created by the convection currents of moving
  molten metals that generate Earth’s magnetic field are not evenly
  distributed throughout the liquid outer core. Due to this, the
  strength of Earth’s magnetic field varies from place to place
  underground. It is also the reason that the Magnetic North and South
  Poles are not antipodal, meaning that the imaginary line connecting
  the two does not pass straight through the center of the Earth. All of
  these factors combine in such ways that the parts of the Earth’s
  magnetic field that emerge from the bottom of the world at differing
  angles with the Earth’s surface (i.e., not perpendicularly) do not
  also emerge at the Magnetic South Pole as the perpendicular lines of
  force do. Instead, the location where they do emerge, the Geomagnetic
  South Pole, and the spot where they re-enter the planet, the
  Geomagnetic North Pole, are derived mathematically as a best fit for
  imaginary ends of a solid, dipolar bar magnet that account for the
  properties of the Earth’s magnetic field, both on the surface and
  around the planet.

  Once up out of the ground and above the Earth, the magnetic lines of
  force from the Geomagnetic South Pole even out more uniformly. They
  are not perpendicular, nor even all that vertical. Extending out into
  space, they curve northward to surround and protect the Earth from the
  solar wind as the magnetosphere, the northern part of which glows in
  the solar wind as the Northern Lights of the Aurora Borealis. North of
  the Arctic Circle, they curve downward once again to re-enter the
  Earth at the Geomagnetic North Pole, located on Ellesmere Island in
  Canada, northwest of Greenland, to form closed loops of magnetic
  force. The Geomagnetic North Pole also moves around from year to year,
  not as much as the Magnetic North Pole, but for the same reasons.

  Although a mathematical derivation, the Geomagnetic North Pole is real
  enough. Like the Magnetic North Pole, the north end of a compass
  needle likes to point there, too. Truth be told, most of the time,
  compass needles actually point to somewhere near the top of the world
  between the Magnetic and Geomagnetic North Poles. One last point: If
  the Earth’s magnetic field were generated by a large, imaginary,
  solid, dipolar bar magnet that passed through the center of the
  Earth’s solid inner core instead of by electrical currents generated
  by moving molten metals in the outer core, the Magnetic North Pole and
  Geomagnetic North Pole would be at the same location. The
  perpendicular lines of magnetic force would re-enter the Earth at dead
  center, surrounded by curved ones that re-enter at differing angles.

  Most compasses sold are devised to work best in the Northern
  Hemisphere. A magnetic binnacle compass has a free-spinning compass
  card that aligns with an agonic line or an isogonic line of the
  Earth’s magnetic field. Electronic fluxgate compasses measure the
  relative strength of electromagnetic flux passing through two coils of
  wire arranged perpendicularly to deduce the direction of the Earth’s
  magnetic field. The Earth’s magnetic field intensity is between 25,000
  and 65,000 nano-teslas. By comparison, a strong refrigerator magnet
  has an intensity of about 10 million nano-teslas, some 150 to 400
  times stronger than the Earth’s magnetic field.

  Finally, about the elephant in the room. On that day back in grammar
  school when we sprinkled iron filings on white paper laid over a
  dipole magnet, we learned that magnetic lines of force flow from a
  magnet’s north pole to its south pole. We also learned that opposite
  poles attract and like poles repel. So, why would the Earth’s magnetic
  field emanate from its Magnetic South Pole and re-enter the planet at
  its Magnetic North Pole? And why would the north ends of magnetized
  needles in compasses all around the Northern Hemisphere want to point
  North? Well, it does not, and they do not! The Magnetic North Pole of
  the Earth is really its Magnetic South Pole! Scientists sidestep this
  fact by referring to the Magnetic North Pole as the “north-seeking”
  pole, as if to say that the magnetic patterns of force emanating from
  the Magnetic South Pole (really the Magnetic North Pole) are seeking
  the pole in the Northern Hemisphere, regardless of its polarity. The
  same is true of the Geomagnetic North and South Poles as well.

  If this is disillusioning, it may be gratifying to learn that some
  scientists believe the increased rate of movement of the Magnetic
  North Pole may signal the early stages of a geomagnetic field reversal
  where the Magnetic North and South Poles would flip and exchange
  places, perhaps back into their “correct” positions. Rocks have
  revealed that at least 184 geomagnetic field reversals have occurred
  over the last 83 million years, roughly between every 100,000 to 1
  million years, and that these reversals have usually required between
  1,000 and 10,000 years to complete. The last complete and enduring
  geomagnetic field reversal occurred 786,000 years ago, and it may have
  occurred within the span of a single human lifetime! A brief,
  temporary reversal occurred 41,000 years ago during the Ice Age, but
  it lasted “only” 440 years before reverting. The hypothesized triggers
  of these recurring geomagnetic field reversals are extra-terrestrial
  extinction-level impact events, rock slabs the size of a continent
  sinking into the area between the mantle and the liquid outer core,
  massive plate tectonic subductions and unknown events that may have
  caused large-scale disruptions of the molten metal geodynamo running
  within the liquid outer core, thereby weakening the Earth’s magnetic
  field, making a rearrangement of the fields more likely, even leading
  to a geomagnetic field reversal.

  /Lenox Grasso is an instructor coordinator for the American Sailing
  Association./


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