Magnetosphere - Earth's Magnetic Field

Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole and the other near the geographic south pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3° from the planet's axis of rotation. The cause of the field is probably explained by dynamo theory. The magnetic field extends several tens of thousands of kilometres into space as the magnetosphere.

Magnetic poles

Magnetic declination from true north in 2000.The locations of the magnetic poles are not static but wander as much as 15km every year (Dr. David P. Stern, emeritus Goddard Space Flight Center, NASA). The pole position is usually not that indicated on many charts and many magnetic pole marking brings a confusion as to what is being located at the given positions.

The Geomagnetic Pole positions are usually not close to the position that commercial cartographers place "Magnetic Poles." "Geomagnetic Dipole Poles", "IGRF Model Dip Poles", and "Magnetic Dip Poles" are variously used to denote the magnetic poles.

The Earth's field is changing in size and position. The two poles wander independently of each other and are not at directly opposite positions on the globe. Currently the south magnetic pole is farther from the geographic south pole than the north magnetic pole is from the north geographic pole.

Field characteristics

The field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated motions of electrons (negatively charged particles) within iron atoms. The Earth's core, however, is hotter than 1043 K, the Curie point temperature at which the orientations of electron orbits within iron become randomized. Such randomization tends to cause the substance to lose its magnetic field. Therefore the Earth's magnetic field is caused not by magnetized iron deposits, but mostly by electric currents in the liquid outer core.

Another feature that distinguishes the Earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field. Electric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations which can deflect surface magnetic fields by as much as one degree.

Magnetic field variations

The strength of the field at the Earth's surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of South America and South Africa to over 60 microteslas (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.

Magnetometers detect minute deviations in the Earth's magnetic field caused by iron artifacts, kilns, some types of stone structures, and even ditches and middens in geophysical survey. Using the magnetic instruments adapted from airborne devices developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. The basalt - the iron-rich, volcanic rock making up the ocean floor - contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.

In October 2003, the Earth's magnetosphere was hit by a solar flare causing a brief but intense geomagnetic storm, provoking unusual displays of aurorae.

Geomagnetic Reversal - Pole Shifts

Based upon the study of lava formations in Hawaii, it has been deduced that the Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 250,000 years. The last such event, called the Brunhes-Matuyama reversal, occurred some 780,000 years ago.

The mechanism responsible for geomagnetic reversals is not well understood. Some scientists have produced models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontaneously migrate from one orientation to the other over the course of a few hundred to a few thousand years. Other scientists propose that the geodynamo first turns itself off, either spontaneously or through some external action like a comet impact, and then restarts itself with the magnetic "North" pole pointing either North or South. External events are not likely to be routine causes of magnetic field reversals due to the lack of a correlation between the age of impact craters and the timing of reversals. Regardless of the cause, when magnetic "North" reappears in the opposite direction this is a reversal, whereas turning off and returning in the same direction is called a geomagnetic excursion.

Using a magnetic detector (a variant of a compass), scientists have measured the historical direction of the Earth's magnetic field, by studying the layered iron-rich lava rocks. This is possible as each layer has been found to maintain the original magnetic field at its time of cooling. They have found that the poles have shifted a number of times throughout the past.

Magnetic Field Decay

The earth's magnetic field strength was measured by Carl Friedrich Gauss in 1835 and has been repeatedly measured since then, showing an exponential decay with a half-life of about 1400 years. This could also be stated as a relative decay of about 10% to 15% over the last 150 years.

Magnetic Field Electrogenerators

Some free-energy enthusiasts claim that the Earth's magnetic field could be used to generate power[4], but such claims are regarded as pseudoscience by many skeptics. Many designs for using the Earth's electromagnetic field and atmospheric electricity have been researched, but have failed to gain any widespread acknowledgement in the scientific community. There is also some energy stored in the form of separated electrical charges, which can provide low direct currents at high voltages. However, ordinary electric motors cannot use this energy directly as a prime mover. Benjamin Franklin developed several motors that used the Earth's fields. Oleg D. Jefimenko has researched several machine designs for tapping the Earth's electromagnetic field.

The Earth's magnetic field can be used as the starting field for a self-excited electric generator. Cromwell Varley discovered in 1867 that an electric generator did not need to be started with a conventional prime mover. He used the Earth's magnetic field to induce enough field strength in the stator windings to get a generator running.

Electrodynamic tethers can induce a current by moving through the planet's magnetic field. When the conductive tether is trailed in a planetary or solar magnetosphere (magnetic field), the tether cuts the field, generates a current, and thereby slows the spacecraft into a lower orbit. The tether's end can be left bare, and this is sufficient to make contact with the ionosphere and allow a current to flow through a phantom loop. A cathode tube may also be placed at the end of the tether. The cathode tube will interact with the planet's magnetic field in the vacuum of space. A double-ended cathode tube tether will allow alternating currents.

Magnetosphere - Earth's Magnetic Field Wikipedia

In the News ...

Earth's 6-Year Twitch Changes Day Length   Live Science - July 10, 2013
Periodic wobbles in Earth's core change the length of a day every 5.9 years. Teasing out this subtle cycle, which subtracts and adds mere milliseconds to each day, also revealed a match between abrupt changes in the length of day and Earth's magnetic field. During these short-lived lurches in the magnetic field intensity, events called geomagnetic jerks, Earth's day also shifts by 0.1 millisecond, the researchers report. Since 1969, scientists have detected 10 geomagnetic jerks lasting less than a year. Seemingly negligible, these fleeting variations are mighty to those who study the planet and its core. All of a sudden, a planet changes its spin like a figure skater open or closing her arms. The rotational effect helps scientists understand what's happening inside the Earth's core. Shifts in the magnetic field also provide clues to the inaccessible iron core. But their source remains a mystery.

Why Earth's Magnetic Field Is Wonky   Live Science - July 18, 2012

The solution to a long-standing puzzle, why magnetic north sits off the coast of Canada, rather than at the North Pole, may have been found in the strange, lopsided nature of Earth's inner core. The inner core is a ball of solid iron about 760 miles (1,220 kilometers) wide. It is surrounded by a liquid outer core (mostly iron and nickel), a rocky, viscous mantle layer and a thin, solid crust. As the inner core cools, crystallizing iron releases impurities, sending lighter molten material into the liquid outer core. This upwelling, combined with the Earth's rotation, drives convection, forcing the molten metal into whirling vortices. These vortices stretch and twist magnetic field lines, creating Earth’s magnetic field. Currently, the center of the field, called an axis, emerges in the Arctic Ocean west of Ellesmere Island, about 300 miles (500 kilometers) from the geographic North Pole.

Can humans sense the Earth's magnetism?   PhysOrg - June 21, 2011
For migratory birds and sea turtles, the ability to sense the Earth's magnetic field is crucial to navigating the long-distance voyages these animals undertake during migration. Humans, however, are widely assumed not to have an innate magnetic sense.

Humans May Have 'Magnetic' Sixth Sense   Live Science - June 21, 2011
Humans may have a sixth sense after all, suggests a new study finding that a protein in the human retina, when placed into fruit flies, has the ability to detect magnetic fields.

Human eye protein senses Earth's magnetism   BBC - June 21, 2011
A light-sensitive protein in the human eye has been shown to act as a "compass" in a magnetic field, when it is present in flies' eyes.

Reading Earth's magnetic history   PhysOrg - March 4, 2011
In order to date environmental events from Earth's history such as meteorite impacts or climate change - geologists have long studied variations in slow-growing seafloor sedimentary rocks called ferromanganese crusts that build up in layers over the eons. The layers can be dated by various means, such as by analyzing radioactive isotopes, but those methods don't provide accurate dating on small scales: a millimeter of rock, for example, can include information that spans as much as hundreds of thousands of years.

Compass Direction, True North Parting Ways   Discovery - March 4, 2011
Earth's magnetic field is carting away toward Russia at a rate of about 40 miles a year. The shift widens the distance between true north and magnetic north, which is the direction a compass needle points. The phenomenon is normal, though it does have implications for modern life. The planet's magnetic field is on the move, a normal enough phenomenon, but one that has some rather bizarre implications, such as the need to renumber airport runways. Tampa International Airport on Florida's west coast just finished renaming its three runways, a laborious project that interrupted airport traffic for a month while runways were shut down for repainting.

African rocks record ancient magnetic field   BBC - May 4, 2010
Scientists have managed to push back the date for the earliest known presence of a magnetic field on Earth by about 250 million years.

Monarch Butterflies Reveal a Novel Way in Which Animals Sense Earth's Magnetic Field   Science Daily - January 27, 2010
Building on prior investigation into the biological mechanisms through which monarch butterflies are able to migrate up to 2,000 miles from eastern North America to a particular forest in Mexico each year, neurobiologists at the University of Massachusetts Medical School (UMMS) have linked two related photoreceptor proteins found in butterflies to animal navigation using the Earth's magnetic field.

Robins can see Earth's magnetic field - October 29, 2009
he information, relayed to a specialized light-processing region of the brain called ''cluster N'', helps the robin find its way on migration flights. Experts know birds possess an internal magnetic compass, but there is disagreement about what form it takes. One idea is that tiny magnets in the beak wired to the nervous system detect lines of magnetic force. Another is that magnetic fields are ''seen'' via the eyes using a light-sensitive mechanism. The new research suggests that, for robins at least, the second theory is probably correct. German scientists studied 36 European robins and found birds with damage to ''cluster N'' were unable to orientate themselves using the Earth's magnetic field. But damage to another nerve channel necessary for a beak-sensing system had no effect.

'Magnetricity' observed and measured for the first time   PhysOrg - October 18, 2009
The magnetic equivalent of electricity in a 'spin ice' material: atom sized north and south poles in spin ice drift in opposite directions when a magnetic field is applied. A magnetic charge can behave and interact just like an electric charge in some materials, according to new research led by the London Centre for Nanotechnology.

Ancient Earth's Magnetic Field Was Structured Like Today's Two-pole Model   Science Daily - October 5, 2009
Princeton University scientists have shown that, in ancient times, the Earth's magnetic field was structured like the two-pole model of today, suggesting that the methods geoscientists use to reconstruct the geography of early land masses on the globe are accurate. The findings may lead to a better understanding of historical continental movement, which relates to changes in climate. By taking a closer look at the 1.1 billion-year-old volcanic rocks on the north shore of Lake Superior, the researchers have found that Earth's ancient magnetic field was a geocentric axial dipole -- essentially a large bar magnet centered in the core and aligned with the Earth's spin axis.

Shifts in Earth's Magnetic Field Driven by Oceans?   National Geographic - June 23, 2009

The flow of seawater across Earth's surface could be responsible for small fluctuations in the planet's magnetic field, a controversial new study says. If so, the research would challenge the widely accepted theory that Earth's magnetic field is generated by a churning molten core, or dynamo, in the planet's interior.

Rare Magnetar Discovered: Giant Eruption Reveals 'Dead' Star   Science Daily - June 16, 2009
NASA's Swift satellite reported multiple blasts of radiation from a rare object known as a soft gamma repeater, or SGR. Now, astronomers report an in-depth study of these eruptions using the European Space Agency's XMM-Newton and International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellites.

Giant Eruption Reveals 'Dead' Star   Space Daily - June 18, 2009

An enormous eruption has found its way to Earth after traveling for many thousands of years across space. The dead star belonging to a rare group: the magnetars.

Reversals of Earth's Magnetic Field Explained by Small Core Fluctuations   PhysOrg - April 23, 2009

Based on studies of old volcanic basalt, scientists know that the Earth’s magnetic field reverses at irregular intervals, ranging from tens of thousands to millions of years. Volcanic basalt rock contains magnetite, and when the rock cools, its magnetic properties are frozen, recording the Earth's magnetic field of the time. With this data, scientists estimate that the last magnetic field reversal occurred about 780,000 years ago.

"Warm Plasma Cloak" Discovered Enveloping Earth   National Geographic - January 7, 2009
The magnetosphere - the shield of ions and electrons that envelops Earth
extends far beyond the atmosphere, defending the planet from the harmful solar wind.

The Enigma of the Enchanted Hills   Epoch Times - January 10, 2009

Magnetic-Shield Cracks Found; Big Solar Storms Expected    National Geographic - December 17, 2008
An unexpected, thick layer of solar particles inside Earth's magnetic field suggests there are huge breaches in our planet's solar defenses. These breaches indicate that during the next period of high solar activity, due to start in 2012, Earth will experience some of the worst solar storms seen in decades.

Leaks Found in Earth's Protective Magnetic Field    Live Science - December 17, 2008
Scientists have found two large leaks in Earth's magnetosphere, the region around our planet that shields us from severe solar storms. The leaks are defying many of scientists' previous ideas on how the interaction between Earth's magnetosphere and solar wind occurs: The leaks are in an unexpected location, let in solar particles in faster than expected and the whole interaction works in a manner that is completely the opposite of what scientists had thought.

A Giant Breach in Earth's Magnetic Field    NASA - December 16, 2008
NASA's five THEMIS spacecraft have discovered a breach in Earth's magnetic field ten times larger than anything previously thought to exist. Solar wind can flow in through the opening to "load up" the magnetosphere for powerful geomagnetic storms. But the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.

Here's how it plays out...

Coronal Mass Ejections (CMEs) reach Earth affecting planetary magnetics, sparking geomagnetic storms, shifting ocean and jet stream currents in the Pacific Ring of Fire, creating unusual and extreme global weather patterns, creating unstoppable Earth changes, and affecting the behavior patterns of all sentient life forms.

Lava flows reveal clues to magnetic field reversals PhysOrg - September 25, 2008
Ancient lava flows are guiding a better understanding of what generates and controls the Earth's magnetic field - and what may drive it to occasionally reverse direction. The main magnetic field, generated by turbulent currents within the deep mass of molten iron of the Earth's outer core, periodically flips its direction, such that a compass needle would point south rather than north. Such polarity reversals have occurred hundreds of times at irregular intervals throughout the planet's history - most recently about 780,000 years ago - but scientists are still trying to understand how and why.

Earth's Core, Magnetic Field Changing Fast, Study Says National Geographic - July 1, 2008

Rapid changes in the churning movement of Earth's liquid outer core are weakening the magnetic field in some regions of the planet's surface, a new study says. "What is so surprising is that rapid, almost sudden, changes take place in the Earth's magnetic field," said study co-author Nils Olsen, a geophysicist at the Danish National Space Center in Copenhagen.

Birds Can "See" Earth's Magnetic Field National Geographic - September 27, 2007
To find north, humans look to a compass. But birds may just need to open their eyes, a new study says. Scientists already suspected birds' eyes contain molecules that are thought to sense Earth's magnetic field. In a new study, German researchers found that these molecules are linked to an area of the brain known to process visual information. In that sense, "birds may see the magnetic field," said study lead author Dominik Heyers, a biologist at the University of Oldenburg. Human-made compasses work by using Earth as an enormous magnet and orienting a tiny magnet attached to a needle to the planet's north and south poles.

Magnetic Field Weakening in Stages, Old Ships' Logs Suggest National Geographic - May 12, 2006
Earth's magnetic field is weakening in staggered steps, a new analysis of centuries-old ships logs suggests.The finding could help scientists better understand the way Earth's magnetic poles reverse. The planet's magnetic field flips - north becomes south and vice versa - on average every 300,000 years. However, the actual time between reversals varies widely. The field last flipped about 800,000 years ago, according to the geologic record. Since 1840, when accurate measures of the intensity were first made, the field strength has declined by about 5 percent per century. If this decline is continuous, the magnetic field could drop to zero and reverse sometime within the next 2,000 years. But the field might not always be in steady decline, according to a new study appearing in tomorrow's issue of the journal Science. The data show that field strength was relatively stable between 1590 and 1840.

Geomagnetic flip may not be random after all PhysicsWeb - March 22, 2006
One of the most fascinating natural phenomena on Earth is the flipping of its magnetic field, which has occurred hundreds of times in the last 160 million years. When the magnetic field flips, the North Pole becomes the South Pole and vice versa. The last time this happened was some 780,000 years ago, so we could be heading for another reversal soon. Now, physicists in Italy have found that the frequency of these polarity reversals is not random as previously thought but occurs in clusters, revealing some kind of "memory" of previous events

Movement of North Magnetic Pole is accelerating PhysOrg - December 9, 2005
After some 400 years of relative stability, Earth's North Magnetic Pole has moved nearly 1,100 kilometers out into the Arctic Ocean during the last century and at its present rate could move from northern Canada to Siberia within the next half-century. If that happens, Alaska may be in danger of losing one of its most stunning natural phenomena – the Northern Lights.

Pulsar Gives Insight On Ultra Dense Matter And Magnetic Fields Science Daily - December 20, 2004

A long look at a young pulsar with NASA's Chandra X-ray Observatory revealed unexpectedly rapid cooling, which suggests that it contains much denser matter than previously expected. The pulsar's cool temperature and the vast magnetic web of high-energy particles that surrounds it have implications for the theory of nuclear matter and the origin of magnetic fields in cosmic objects.

Why Does Earth's Magnetic Field Flip? National Geographic - September 27, 2004
Earth's magnetic field has flipped many times over the last billion years, according to the geologic record. But only in the past decade have scientists developed and evolved a computer model to demonstrate how these reversals occur.

Earth's Magnetic Field Is Fading National Geographic - September 9, 2004

The Earth's Magnetics fields appear to be reversing...

Today it is about 10 percent weaker than it was when German mathematician Carl Friedrich Gauss started keeping tabs on it in 1845, scientists say. If the trend continues, the field may collapse altogether and then reverse. Compasses would point south instead of north.

The Earth's magnetic field is fading BBC - December 31, 2003

Scientists have known for some time that the Earth's magnetic field is fading. Like a Kryptonite-challenged Superman, its strength has steadily and mysteriously waned, leaving parts of the planet vulnerable to increased radiation from space. Some satellites already feel the effects. What is uncertain is whether the weakened field is on the way to a complete collapse and a reversal that would flip the North and South Poles. Compasses pointing North would then point South.

Earth's magnetic north pole is racing away from North America. NASA - December 29, 2003