The Earth’s magnetic field plays a major role in protecting people from dangerous radiation and geomagnetic activity that can affect satellite communications and the operation of power grids. And it moves.
Scientists have studied and tracked the movement of the magnetic poles for centuries. The historical movement of these poles indicates a change in the global geometry of the Earth’s magnetic field. It could even signal the beginning of a field reversal – a ‘flip’ between the magnetic north and south poles.
I am a physicist who studies the interaction between the planets and space. While moving the magnetic north pole a little isn’t a problem, a reversal could have a major impact on Earth’s climate and our modern technology. But these reversals don’t happen immediately. Instead, they occur over thousands of years.
Generation of magnetic field
How are magnetic fields like those around Earth generated?
Magnetic fields are generated by moving electric charges. A material that allows charges to move easily in it is called a conductor. Metal is an example of a conductor: people use it to transmit electrical currents from one place to another. The electric current itself simply consists of negative charges, called electrons, moving through the metal. This current generates a magnetic field.
Layers of conductive material are found in the Earth’s liquid iron core. Charge currents move through the core, and the liquid iron also moves and circulates in the core. These movements generate the magnetic field.
Earth is not the only planet with a magnetic field; gas giant planets like Jupiter have a conductive metallic hydrogen layer that generates their magnetic fields.
The movement of these conductive layers within planets results in two types of fields. Larger movements, such as large-scale rotations with the planet, lead to a symmetrical magnetic field with a north and a south pole – comparable to a toy magnet.
These conducting layers may exhibit locally irregular movements due to local turbulence or smaller flows that do not follow the large-scale pattern. These irregularities will manifest themselves in some small deviations in the planet’s magnetic field or in places where the field deviates from a perfect dipole field.
These small-scale deviations in the magnetic field can even lead to changes in the large-scale field over time and possibly even a complete reversal of the polarity of the dipole field, with north turning into south and vice versa. The markings “north” and “south” on the magnetic field refer to their opposite polarities – they are not related to geographic north and south.
Earth’s magnetosphere, a protective bubble
Earth’s magnetic field creates a magnetic ‘bubble’ called the magnetosphere above the upper part of the atmosphere, the ionosphere layer.
The magnetosphere plays an important role in protecting people. It protects and deflects harmful, high-energy cosmic rays, which are created by star explosions and constantly move through the universe. The magnetosphere also interacts with the solar wind, a stream of magnetized gas emitted by the Sun.
The interaction of the magnetosphere and ionosphere with magnetized solar wind creates what scientists call space weather. Typically, the solar wind is mild and there is little to no space weather.
However, there are times when the Sun ejects large clouds of magnetized gas, coronal mass ejections, into space. If these coronal mass ejections reach Earth, their interaction with the magnetosphere can create geomagnetic storms. Geomagnetic storms can cause auroras, which happen when a stream of energetic particles hits the atmosphere and lights up.
During space weather events, there is more dangerous radiation near Earth. This radiation can potentially damage satellites and astronauts. Space weather can also damage large conductive systems, such as large pipelines and power grids, by overloading the currents in these systems.
Space weather events can also disrupt satellite communications and GPS operation, which many people rely on.
Field flips
Scientists map and track the overall shape and orientation of the Earth’s magnetic field using local measurements of the field’s orientation and magnitude and, more recently, models.
The location of the North Magnetic Pole has shifted by about 600 miles (965 kilometers) since it was first measured in 1831. The rate of migration has increased from 10 miles per year to 34 miles per year (16 km to 54 km) in more recent years. This acceleration could indicate the beginning of a reversal of the field, but scientists cannot say for sure from less than 200 years of data.
Earth’s magnetic field reverses on timescales ranging between 100,000 and 1,000,000 years. Scientists can see how often the magnetic field reverses by looking at volcanic rocks in the ocean.
These rocks capture the orientation and strength of Earth’s magnetic field as they formed, so dating these rocks gives a good idea of how Earth’s field has evolved over time.
Field reversals happen quickly from a geological perspective, but slowly from a human perspective. A reversal usually takes a few thousand years, but during this time the orientation of the magnetosphere can shift and expose more of the Earth to cosmic rays. These events can change the concentration of ozone in the atmosphere.
Scientists cannot say with certainty when the next field reversal will occur, but we can continue to map and track the movement of Earth’s magnetic north.
This article is republished from The Conversation, an independent nonprofit organization providing facts and analysis to help you understand our complex world.
It was written by: Ofer Cohen, UMass Lowell.
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Ofer Cohen works for the University of Massachusetts Lowell. The university benefits from every public article written by one of its faculties in terms of fame and visibility. Ofer Cohen received funding from NASA that was somehow related to the article.