How does the Earth's core generate a magnetic field?

The Earth's outer core is in a state of turbulent convection as the result of radioactive heating and chemical differentiation. This sets up a process that is a bit like a naturally occurring electrical generator, where the convective kinetic energy is converted to electrical and magnetic energy. Basically, the motion of the electrically conducting iron in the presence of the Earth's magnetic field induces electric currents. Those electric currents generate their own magnetic field, and as the result of this internal feedback, the process is self-sustaining so long as there is an energy source sufficient to maintain convection.

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Why measure the magnetic field at the Earth's surface? Wouldn't satellites be better suited for space-weather studies?

Satellites and ground-based magnetometers are both important for making measurements of the Earth’s magnetic field. They are not redundant but are instead complementary: Satellites provide good geographical coverage for data collection. Ground-based magnetometers are much less expensive and much easier to install than satellites. An array of...

What are the hazards of magnetic storms?

Our technology-based infrastructure can be adversely affected by rapid magnetic-field variations. This is especially true during “magnetic storms." Because the ionosphere is heated and distorted during storms, long-range radio communication that relies on sub-ionospheric reflection can be difficult or impossible and global-positioning system (GPS...

What is a magnetic storm?

A magnetic storm is a period of rapid magnetic field variation. It can last from hours to days. Magnetic storms have two basic causes: The Sun sometimes emits a strong surge of solar wind called a coronal mass ejection. This gust of solar wind disturbs the outer part of the Earth's magnetic field, which undergoes a complex oscillation. This...

Does the Earth's magnetic field affect human health?

The Earth's magnetic field does not directly affect human health. Humans evolved to live on this planet. High-altitude pilots and astronauts can experience higher levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself. Geomagnetism can also impact the electrically-based technology that we...

What is declination?

At most places on the Earth's surface, the compass doesn't point exactly toward geographic north. The deviation of the compass from true north is an angle called "declination" (or "magnetic declination"). It is a quantity that has been a nuisance to navigators for centuries, especially since it varies with both geographic location and time . It...

Are we about to have a magnetic reversal?

Almost certainly not. Since the invention of the magnetometer in the 1830s, the average intensity of the magnetic field at the Earth's surface has decreased by about ten percent. We know from paleomagnetic records that the intensity of the magnetic field decreases by as much as ninety percent at the Earth's surface during a reversal. But those...

Is the Earth a magnet?

In a sense, yes. The Earth is composed of layers having different chemical compositions and different physical properties. The crust of the Earth has some permanent magnetization, and the Earth’s core generates its own magnetic field, sustaining the main part of the field we measure at the surface. So we could say that the Earth is, therefore, a "...
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Date published: March 8, 2018

New 3D Measurements Improve Understanding of Geomagnetic Storm Hazards

Measurements of the three-dimensional structure of the earth, as opposed to the one-dimensional models typically used, can help scientists more accurately determine which areas of the United States are most vulnerable to blackouts during hazardous geomagnetic storms.

Date published: September 12, 2016

Mapping a Space-Weather Menace to Electric-Power Grids

New strides have been made toward quantifying how geomagnetic storms can interfere with the nation’s electric-power grid systems.  

Date published: May 23, 2006

USGS, NOAA Mark 50 Years of Geomagnetic Research at Corbin, Va.


On May 23, 1956, a research center and observatory opened at Corbin, Va. to continuously monitor the Earth's magnetic field. It was charged by Congress "to enhance geomagnetic field studies and monitoring programs in support of scientific, general public, basic and national security needs of the United States."

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Preparing the Nation for Intense Space Weather
January 31, 2017

Preparing the Nation for Intense Space Weather

Preparing the Nation for Intense Space Weather

Giant Sunspot Erupts on October 24, 2014
January 31, 2017

Giant Sunspot Erupts on October 24, 2014

Active Region 12192 on the sun erupted with a strong flare on October 24, 2014, prominent in the bright light of this image captured by NASA's Solar Dynamics Observatory. This image shows extreme ultraviolet light that highlights the hot solar material in the sun's atmosphere. Credit: NASA

Earth from space
November 7, 2016

Earth from space

Earth from space

December 16, 2013

Hazards: Geomagnetic Storms

Space weather can have important consequences for our lives, such as interference with radio communication, GPS systems, electric power grids, the operation and orientation of satellites, oil and gas drilling, and even air travel as high altitude pilots and astronauts can be subjected to enhanced levels of radiation. It is also during magnetic storms that beautiful aurora

USGS CoreCast
October 16, 2007

Earth Science Week, Continued: Geomagnetism and the Self-Sustaining Dynamo Called Earth

USGS scientist Duane Champion explains the Earth's geomagnetic qualities and the potential for and possible consequences of a geomagnetic shift.

July 29, 2004

PubTalk 7/2004 — Secrets in Stone

The Role of Paleomagnetism in the Evolution of Plate Tectonic Theory Video Presentation

Presentation of the award-winning USGS video "Secrets in Stone" (35 minutes), introduced by Jack Hillhouse, Research Geophysicist, and followed by a tour of the USGS Paleomagnetics Laboratory

  • Crucial discoveries in the early 1960.s were made
What is Space weather

Space weather