Jump to content

Any changes to Compass Devarition

Recommended Posts

Scientific American Are the Earth's magnetic poles moving? How do navigators adjust to this change?


  • The answer comes from Paul Perreault, marketing manager for university and government research programs at Trimble Navigation Ltd., a manufacturer of advanced navigation systems.
Image: Canadian National Geomagnetism Program
WANDERING POLE. The North magnetic pole has moved steadily northward at an average rate of 10 kilometers per year since it was first located in 1831.
The earth's geographic poles are generally right where you would expect them to be: at the two opposing points about which the Earth seems to rotate. Magnetic poles used in compass navigation are another matter altogether. And neither pole pair is completely stationary.

The North magnetic pole is at a point where a dipping compass--a compass that allows the needle to move freely in a vertical plane (as opposed to the horizontal needle movements seen in most compasses)--points straight down into the earth. The South magnetic pole is the point where a dipping compass points up. A dipping compass points horizontally on the Earth's magnetic equator, also called the Earth's dip equator.

The magnetic poles are quite distant from their geographic counterparts. The North magnetic pole is located to the south in Northern Canada; the geographic South pole is at the center of the Antarctic continent, but the magnetic pole is hundreds of miles away, near the coast. In regions near the magnetic poles, compasses are virtually useless.

Complicating this issue is that these pole positions are not static--for either magnetic or geographic poles. The location of the North geographic pole wanders in a small erratic circle-like path, called the "Chandler wobble." This motion is less than 6 meters per year on the surface; a worldwide network of very precise global positioning satellite (GPS) receivers is used to determine this wander.


The magnetic poles are far more restless. They move under the influence of the dynamo currents in the Earth's core, as well as electric currents flowing in the ionosphere, the radiation belts and the Earth's magnetosphere. The North magnetic pole seems to be moving northward at an average rate of 10 kilometers per year. Yet there is also some elliptical motion to this general trend. On any given day, the magnetic pole may be as much as 80 kilometers away from its average position, depending on the geomagnetic disturbances in the ionosphere and magnetosphere.

Modern navigators normally are not affected by the wandering of the poles because they can regularly determine their position from satellites and Earth-based observatories. The degree of difference between the position of these two poles when seen at various locations is called magnetic declination. These angles allow navigators to determine their actual geographic position. Charts and handbooks for navigation regularly update these values and are published by government agencies.

Maritime and air navigation regulations require use of these up-to-date charts and tables. Without GPS, the navigator would use a new version of the chart or table. With GPS, navigators update their receiver database by purchasing new data from the Government or from the GPS manufacturer and loading it into the onboard GPS unit.


Link to post
Share on other sites

From; Nature 09 January 2019

Earth’s magnetic field is acting up and geologists don’t know why
Erratic motion of north magnetic pole forces experts to update model that aids global navigation.
Alexandra Witze

Something strange is going on at the top of the world. Earth’s north magnetic pole has been skittering away from Canada and towards Siberia, driven by liquid iron sloshing within the planet’s core. The magnetic pole is moving so quickly that it has forced the world’s geomagnetism experts into a rare move.

On 15 January, they are set to update the World Magnetic Model, which describes the planet’s magnetic field and underlies all modern navigation, from the systems that steer ships at sea to Google Maps on smartphones.

The most recent version of the model came out in 2015 and was supposed to last until 2020 — but the magnetic field is changing so rapidly that researchers have to fix the model now. “The error is increasing all the time,” says Arnaud Chulliat, a geomagnetist at the University of Colorado Boulder and the National Oceanic and Atmospheric Administration’s (NOAA’s) National Centers for Environmental Information.

The problem lies partly with the moving pole and partly with other shifts deep within the planet. Liquid churning in Earth’s core generates most of the magnetic field, which varies over time as the deep flows change. In 2016, for instance, part of the magnetic field temporarily accelerated deep under northern South America and the eastern Pacific Ocean. Satellites such as the European Space Agency’s Swarm mission tracked the shift.

By early 2018, the World Magnetic Model was in trouble. Researchers from NOAA and the British Geological Survey in Edinburgh had been doing their annual check of how well the model was capturing all the variations in Earth’s magnetic field. They realized that it was so inaccurate that it was about to exceed the acceptable limit for navigational errors.

Wandering pole

“That was an interesting situation we found ourselves in,” says Chulliat. “What’s happening?” The answer is twofold, he reported last month at a meeting of the American Geophysical Union in Washington DC.

First, that 2016 geomagnetic pulse beneath South America came at the worst possible time, just after the 2015 update to the World Magnetic Model. This meant that the magnetic field had lurched just after the latest update, in ways that planners had not anticipated.

d41586-019-00007-1_16383826.jpg d41586-019-00007-1_16383826.jpg

Source: World Data Center for Geomagnetism/Kyoto Univ.

Second, the motion of the north magnetic pole made the problem worse. The pole wanders in unpredictable ways that have fascinated explorers and scientists since James Clark Ross first measured it in 1831 in the Canadian Arctic. In the mid-1990s it picked up speed, from around 15 kilometres per year to around 55 kilometres per year. By 2001, it had entered the Arctic Ocean — where, in 2007, a team including Chulliat landed an aeroplane on the sea ice in an attempt to locate the pole.

In 2018, the pole crossed the International Date Line into the Eastern Hemisphere. It is currently making a beeline for Siberia.

The geometry of Earth’s magnetic field magnifies the model’s errors in places where the field is changing quickly, such as the North Pole. “The fact that the pole is going fast makes this region more prone to large errors,” says Chulliat.

To fix the World Magnetic Model, he and his colleagues fed it three years of recent data, which included the 2016 geomagnetic pulse. The new version should remain accurate, he says, until the next regularly scheduled update in 2020.

Core questions

In the meantime, scientists are working to understand why the magnetic field is changing so dramatically. Geomagnetic pulses, like the one that happened in 2016, might be traced back to ‘hydromagnetic’ waves arising from deep in the core1. And the fast motion of the north magnetic pole could be linked to a high-speed jet of liquid iron beneath Canada2.

The jet seems to be smearing out and weakening the magnetic field beneath Canada, Phil Livermore, a geomagnetist at the University of Leeds, UK, said at the American Geophysical Union meeting. And that means that Canada is essentially losing a magnetic tug-of-war with Siberia.

“The location of the north magnetic pole appears to be governed by two large-scale patches of magnetic field, one beneath Canada and one beneath Siberia,” Livermore says. “The Siberian patch is winning the competition.”

Which means that the world’s geomagnetists will have a lot to keep them busy for the foreseeable future.

Link to post
Share on other sites

NASA; Magnetic Reversal

Nov. 30, 2011
2012: Magnetic Pole Reversal Happens All The (Geologic) Time
Schematic illustration of Earth's magnetic field.
Credits: Peter Reid, The University of Edinburgh

Scientists understand that Earth's magnetic field has flipped its polarity many times over the millennia. In other words, if you were alive about 800,000 years ago, and facing what we call north with a magnetic compass in your hand, the needle would point to 'south.' This is because a magnetic compass is calibrated based on Earth's poles. The N-S markings of a compass would be 180 degrees wrong if the polarity of today's magnetic field were reversed. Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth's destruction. But would there be any dramatic effects? The answer, from the geologic and fossil records we have from hundreds of past magnetic polarity reversals, seems to be 'no.'

Reversals are the rule, not the exception. Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal. A reversal happens over hundreds or thousands of years, and it is not exactly a clean back flip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in "recent" years, when dinosaurs walked Earth a reversal was more likely to happen only about every one million years.

Sediment cores taken from deep ocean floors can tell scientists about magnetic polarity shifts, providing a direct link between magnetic field activity and the fossil record. The Earth's magnetic field determines the magnetization of lava as it is laid down on the ocean floor on either side of the Mid-Atlantic Rift where the North American and European continental plates are spreading apart. As the lava solidifies, it creates a record of the orientation of past magnetic fields much like a tape recorder records sound. The last time that Earth's poles flipped in a major reversal was about 780,000 years ago, in what scientists call the Brunhes-Matuyama reversal. The fossil record shows no drastic changes in plant or animal life. Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores. This is also proof that a polarity reversal would not affect the rotation axis of Earth, as the planet's rotation axis tilt has a significant effect on climate and glaciation and any change would be evident in the glacial record.

Earth's polarity is not a constant. Unlike a classic bar magnet, or the decorative magnets on your refrigerator, the matter governing Earth's magnetic field moves around. Geophysicists are pretty sure that the reason Earth has a magnetic field is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal. This process can also be modeled with supercomputers. Ours is, without hyperbole, a dynamic planet. The flow of liquid iron in Earth's core creates electric currents, which in turn create the magnetic field. So while parts of Earth's outer core are too deep for scientists to measure directly, we can infer movement in the core by observing changes in the magnetic field. The magnetic north pole has been creeping northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century.

Another doomsday hypothesis about a geomagnetic flip plays up fears about incoming solar activity. This suggestion mistakenly assumes that a pole reversal would momentarily leave Earth without the magnetic field that protects us from solar flares and coronal mass ejections from the sun. But, while Earth's magnetic field can indeed weaken and strengthen over time, there is no indication that it has ever disappeared completely. A weaker field would certainly lead to a small increase in solar radiation on Earth – as well as a beautiful display of aurora at lower latitudes - but nothing deadly. Moreover, even with a weakened magnetic field, Earth's thick atmosphere also offers protection against the sun's incoming particles.

The science shows that magnetic pole reversal is – in terms of geologic time scales – a common occurrence that happens gradually over millennia. While the conditions that cause polarity reversals are not entirely predictable – the north pole's movement could subtly change direction, for instance – there is nothing in the millions of years of geologic record to suggest that any of the 2012 doomsday scenarios connected to a pole reversal should be taken seriously. A reversal might, however, be good business for magnetic compass manufacturers.

Link to post
Share on other sites

Perhaps our measurement scale has become so accurate we are worried about stuff we never used to worry about too much?


Just get a new deviation card every few years which we should do anyway. 


its been happening for ages.

  • Upvote 1
Link to post
Share on other sites

Hey I'm no rocket scientist and I've wrong many times but...


- I don't think there is anything called Compass Devarition.  Deviation yes, Devarition I'm not so familiar with

- I think you are talking about Magnetic Variation, which is the difference between True North and Magnetic North

- I don't think you need worry about your ship's Deviation Card, as this is a reflection of the ship's effect on the accuracy of your compass

- it's all Trump's fault

Link to post
Share on other sites

Compass rose on all charts already has the magnetic variation, the date that was determined, and the rate of change per year. So if you are determining your variation, you need to refer to the chart for your specific area and determine the correct variation for your year.


i.e. for Approaches to Auckland, its 19 deg 30 min east @ 2009 (moving east at 2 mins / year)


I'm assuming the rate of change for the NZ area hasn't changed substantially greater than 2 mins / year, and if you are worried about it, just update your charts.

I'd be impressed if anyone can steer as accurately as the errors anyway (we're talking 1/3rd of a degree over the last 10 years for Auckland).


If you are navigating in the arctic circle its a different story, but arctic explorers have long known you can't use a compass for nav in high latitudes.

  • Downvote 1
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...