geomagnetic field

Introduction
Observations of Earth’s magnetic field
- Representation of the field
- Measurement of the field
Characteristics of Earth’s magnetic field
- Dipolar field
- Outer magnetic field
Sources of the steady magnetic field
- The geomagnetic dynamo
- Crustal magnetization
- The ionospheric dynamo
- The ring current
- The magnetopause current
- The magnetotail current
- Field-aligned currents
- Convective electrojets
Sources of variation in the steady magnetic field
- Secular variation of the main field
- Reversals of the main field
- Variations in the ionospheric dynamo current
- Magnetic storms—growth of the ring current
  - Cause of magnetic storms
  - Magnetic reconnection
  - Generation of a magnetospheric electric field
  - Decay of the ring current
- Magnetospheric substorms—unbalanced flux transfer
  - Growth phase
  - Expansion phase
- Magnetohydrodynamic waves—magnetic pulsations

References & Edit History Quick Facts & Related Topics

Images & Videos

Understand Earth's geomagnetic field through the dynamo effect principle

Map of the northern polar region showing the tracked movement of Earth's north magnetic pole from 1900 to a projected location in 2020. The pole's positions are marked by labeled dots moving from northern Canada across the Arctic Ocean toward Russia, with nearby landmasses including Alaska, Canada, and Russia indicated.

particle motion in Earth's magnetic field

northern portion of magnetopause current

At a Glance

geomagnetic field summary

Related Questions

How are geomagnetic poles different from geographic poles?
How can particles from the solar wind enter Earth’s magnetosphere?
How do electric currents in Earth’s liquid outer core generate the geomagnetic field?
How do magnetic observatories continuously record changes in Earth’s geomagnetic field?
How do rocks on the ocean floor provide evidence for geomagnetic reversals?
How do solar flares and coronal holes cause geomagnetic storms?
How does Earth’s rotation help create the geomagnetic field?
How does a proton-precession magnetometer measure the strength of Earth’s magnetic field?
How does paleomagnetism provide evidence that continents have moved over time?
How does the Coriolis force twist fluid motion in Earth’s outer core?
How does the bow shock deflect solar-wind particles around Earth?
How does the freezing of Earth’s liquid core release energy for the geomagnetic dynamo?
How does the solar wind shape Earth’s magnetosphere?
How far is Earth’s magnetic dipole tilted from its rotation axis?
How is Earth’s geomagnetic field similar to the field around a bar magnet?
How might a weak magnetic field during a reversal allow more cosmic rays to reach Earth?
How often has Earth’s magnetic field reversed during geologic history?
How were the Van Allen radiation belts discovered by Explorer 1?
What are the omega effect and alpha effect in the geomagnetic dynamo?
What are the sudden-commencement, initial, main, and recovery phases of a geomagnetic storm?
What does a compass measure in Earth’s magnetic field?
What happens at the magnetopause between the solar wind and Earth’s magnetosphere?
What happens to Earth’s dipole magnetic field during a polarity reversal?
Where does magnetic reconnection occur on Earth’s dayside and nightside?
Why are Earth’s geomagnetic poles not located exactly at the North and South geographic poles?
Why are magnetic field lines considered a visualization tool rather than physical objects?
Why can regional geomagnetic anomalies affect compass readings?
Why do auroras usually appear in oval regions around the geomagnetic poles?
Why do symmetrical magnetic stripes form on opposite sides of the Mid-Atlantic Ridge?
Why does Earth’s magnetic field depart from a simple dipole shape far from the planet?
Why does the South Atlantic region have an unusually weak geomagnetic field?
Why is Earth’s geomagnetic field not produced by a giant bar magnet inside the planet?
Why is Earth’s magnetic field strongest near the magnetic poles?
Why is Earth’s magnetosphere compressed on the side facing the Sun?
Why is the geomagnetic dynamo the leading explanation for Earth’s main magnetic field?
Why must Earth’s magnetic field be continuously regenerated in the core?
Why must the fluid in Earth’s outer core conduct electricity for the dynamo to work?
Why was the theory of a permanently magnetized Earth rejected?

Science Earth Science, Geologic Time & Fossils Earth Sciences

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External Websites

Massachusetts Institute of Technology - MIT News - Origins of EarthÂ’s magnetic field remain a mystery
Geosciences LibreTexts - EarthÂ’s Magnetic Field
National Center for Biotechnology Information - PubMed Central - New perspectives in the study of the Earthï¿½s magnetic field and climate connection: The use of transfer entropy
IOPscience - Journal of Physics: Conference Series - The multifractality of the internal geomagnetic field
APS Physics - How Earthï¿½s Magnetic Field Influences Flows in the Planetï¿½s Core
NASA Science - Flip Flop: Why Variations in Earthï¿½s Magnetic Field Arenï¿½t Causing Todayï¿½s Climate Change
USGS - Introduction to Geomagnetism
Australian Government - Geoscience Australia - Geomagnetism
University of Colorado Boulder - Geomagnetism: Theories of Since 1900
Dartmouth Digital Commons - Characterizing the Geomagnetic Field at High Southern Latitudes: Evidence From the Antarctic PeninsulaEvidence From the Antarctic Peninsula (PDF)
Space.com - Earth's magnetic field: Explained

geomagnetic field

geophysics

Also known as: Earth’s magnetic field, geomagnetism, terrestrial magnetism(Show More)

Written by

Robert L. McPherron

Professor of Geophysics and Space Physics, University of California, Los Angeles.

Robert L. McPherron

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 1, 2026 •History

geomagnetic field, magnetic field associated with Earth. It is primarily dipolar (i.e., it has two poles, the geomagnetic North and South poles) on Earth’s surface. Away from the surface the dipole becomes distorted. In the 1830s the German mathematician and astronomer Carl Friedrich Gauss studied Earth’s magnetic field and concluded that the principal dipolar component had its origin inside Earth instead of outside. He demonstrated that the dipolar component was a decreasing function inversely proportional...

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