Earth's magnetic field

Earth's magnetic field
Public domain · source
Name	Earth's magnetic field
Type	Planetary magnetic field
Strength	~25–65 μT at surface
Generated by	Outer core
Discovery	William Gilbert

Earth's magnetic field is the magnetostatic field surrounding the Earth produced primarily by motion in its liquid Outer core and modulated by interactions with the Sun and solar wind. It extends from the planet's interior into space to form the magnetosphere, protects the Ionosphere and Atmosphere from charged particles, and provides a basis for compass-based navigation used historically by explorers such as those on Age of Discovery voyages. Measurements by missions like Explorer 1, Pioneer 10, and Cluster II have refined models such as the International Geomagnetic Reference Field.

Overview

The planetary-scale magnetic field resembles, to first order, a dipole tilted about 11° relative to the rotation axis and displaced slightly from the planet's center; this dipole approximation underlies the Gauss coefficients used in paleomagnetism studies like those associated with the Geologic time scale and controversies in Plate tectonics. Surface intensities range roughly from 25 to 65 microteslas, varying geographically over continents such as Africa, Antarctica, Australia, South America, and Eurasia and tracked by observatories including Geomagnetic Observatory networks and satellite programs like Swarm.

Origin and geodynamo

Generation of the field is explained by the geodynamo mechanism in the convecting metallic Outer core composed chiefly of iron and nickel with light element admixtures; buoyancy-driven convection, influenced by Coriolis force from planetary rotation, organizes helical flows that amplify magnetic fields via magnetohydrodynamics processes described in theories advanced by researchers influenced by work at institutions such as the Carnegie Institution for Science and Geophysical Laboratory. Heat loss across the Core–mantle boundary and inner core growth drive compositional convection, while laboratory experiments at places like Lawrence Livermore National Laboratory and numerical simulations from groups at Imperial College London and Princeton University reproduce self-sustaining dynamos and secular variation patterns quantified through the Magnetic Reynolds number.

Structure and properties

The field comprises a large-scale internal field dominated by the dipole moment, and smaller-scale crustal magnetization recorded in rocks studied in Paleomagnetism by researchers at institutions like Scripps Institution of Oceanography; external fields arise in the Magnetosphere and Ionosphere, influenced by phenomena such as Aurorae observed over polar regions including Arctic and Antarctic. Key properties include intensity, inclination, and declination mapped globally, and anisotropy linked to features like the South Atlantic Anomaly over Brazil and parts of South Africa and Argentina. Thermal and electrical conductivities in the Outer core and Lower mantle control field diffusion timescales tied to the Magnetic diffusivity concept used in models at national centers such as NASA and European Space Agency.

Temporal variations and reversals

The field exhibits secular variation on timescales from years to millennia monitored by arrays like the INTERMAGNET network and satellite series including Ørsted and CHAMP. Over geological time, polarity reversals recorded in oceanic crust at spreading centers like the Mid-Atlantic Ridge produce magnetic stripes that underpin the marine magnetic anomaly evidence supporting Plate tectonics and the geomagnetic polarity timescale used by geologists at institutions such as the United States Geological Survey. Excursions and full reversals, including the Brunhes–Matuyama reversal, occur irregularly; studies by teams at Lamont–Doherty Earth Observatory and Institute of Geology use paleomagnetic sampling of volcanic sequences and sediments to reconstruct reversal processes and durations.

Interaction with the solar wind and magnetosphere

When the solar wind impacts the Magnetosphere, it compresses the dayside field and stretches the nightside into a magnetotail, driving reconnection events studied in missions such as ACE (spacecraft), THEMIS, and MMS. These interactions produce geomagnetic storms that affect systems monitored by agencies like the National Oceanic and Atmospheric Administration and European Space Agency, stimulate auroral displays near regions like Svalbard and Scandinavia, and inject radiation into the Van Allen radiation belts discovered by James Van Allen with Explorer 1.

Effects on life, navigation, and technology

Biological organisms including migratory Arctic terns, Loggerhead sea turtles, and some bacteria use magnetoreception hypothesized to involve magnetite particles or radical-pair mechanisms investigated by groups at University of Oxford and Max Planck Institute for Biophysics. Human navigation historically relied on the magnetic compass during the Age of Sail and modern navigation integrates geomagnetic models in systems like Global Positioning System augmentation and aeronautical flight planning overseen by authorities such as Federal Aviation Administration. Technological impacts include induced currents in power grids during geomagnetic storms (case studies at Hydro-Québec), disruption of satellite electronics examined by teams at Jet Propulsion Laboratory, and errors in directional drilling mitigated in the oil industry by services from firms like Schlumberger.

Measurement and mapping methods

Measurements employ ground observatories, shipborne surveys across oceans like the Pacific Ocean and Indian Ocean, airborne surveys over terrains such as Canadian Shield, and satellite missions including Magsat, Ørsted, CHAMP, and Swarm. Techniques encompass vector magnetometry, scalar magnetometry, aeromagnetic surveying, and paleomagnetic sampling; data feed global models like the International Geomagnetic Reference Field and regional models used by agencies such as British Geological Survey and Geoscience Australia. Laboratory methods include superconducting quantum interference devices developed at Boulder, Colorado laboratories and rock magnetic analysis conducted in facilities like those at University of Cambridge.

Category:Geomagnetism