terrestrial magnetism

terrestrial magnetism
Name	Terrestrial magnetism
Field	Geophysics
Major figures	William Gilbert; Carl Friedrich Gauss; Kristian Birkeland; Walter M. Elsasser; J. A. Jacobs
Institutions	United States Geological Survey; British Geological Survey; Institut de Physique du Globe de Paris; Scripps Institution of Oceanography; Lamont–Doherty Earth Observatory

terrestrial magnetism is the study of the magnetic properties and magnetic field of the Earth and its interactions with space, atmosphere, and living systems. This multidisciplinary subject spans observational programs, theoretical models, laboratory experiments, and applications ranging from navigation to space weather prediction. Research draws on expertise from historical figures, national agencies, and contemporary observatories to resolve the dynamics of the geomagnetic field and its consequences.

Overview and Historical Development

The scientific investigation of terrestrial magnetism traces from antiquity through Renaissance experiments to modern geophysics, involving figures such as William Gilbert, Galileo Galilei, Pierre-Simon Laplace, Alexander von Humboldt, and Carl Friedrich Gauss who established global observational networks and mathematical descriptions. Observatories including Royal Observatory, Greenwich, Kew Observatory, International Geophysical Year, Magnetic Observatory, Helsinki, and institutions like United States Geological Survey and British Geological Survey standardized measurement methods and catalogues. Explorers and cartographers such as James Cook, Alexander von Humboldt, and Ferdinand Magellan integrated magnetic declination into navigation; expeditions by Charles Darwin and surveys by John Herschel contributed magnetic data. Theoretical milestones were advanced by Michael Faraday, James Clerk Maxwell, Walter M. Elsasser, Edward Bullard, and John A. Jacobs who connected magnetism to core dynamics, while laboratory work in magnetism was pursued at institutions including Royal Society, Max Planck Society, and École Normale Supérieure.

Earth's Magnetic Field: Structure and Properties

The geomagnetic field comprises large-scale dipolar components and smaller non-dipolar anomalies characterized by models such as the International Geomagnetic Reference Field (IGRF) and spherical harmonic representations developed by Gauss and modern refinements from NASA, European Space Agency, and research centers like Scripps Institution of Oceanography. Field properties—declination, inclination, and intensity—vary spatially and temporally and are mapped by networks including INTERMAGNET, Swarm (ESA mission), and observatories at Greenwich, Nippon, and Mawson Station. Crustal magnetization produces local anomalies catalogued in regional compilations from USGS and Geological Survey of Canada; mantle and ionospheric sources are studied by satellites such as Ørsted (satellite), CHAMP (satellite), and MAGSAT. Boundary layers like the magnetopause and magnetotail form interactions with the Solar wind, Coronal Mass Ejection, and phenomena observed by Voyager 1, ACE (spacecraft), and Parker Solar Probe.

Geodynamo Theory and Core Processes

Geodynamo theory explains field generation through magnetohydrodynamic convection in the fluid outer core, drawing on work by Florence Nightingale David influences through mathematics, and foundational theory from Walter M. Elsasser, Eugene Parker, S. Chandrasekhar, and Edgar C. Bullard. Numerical simulations are run at centers like Princeton University, University of Cambridge, ETH Zurich, Lamont–Doherty Earth Observatory, and NCAR, using codes influenced by studies at Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and European Centre for Medium-Range Weather Forecasts. Core composition models reference elements studied by Linus Pauling and laboratories such as Carnegie Institution for Science and Argonne National Laboratory, while high-pressure experiments employ facilities at Lawrence Berkeley National Laboratory and European Synchrotron Radiation Facility. Dynamo scaling laws, thermal and compositional convection, inner-core growth, and coupling mechanisms involve contributions from Don L. Anderson, Maurice Ewing, and Gordon McMurtry.

Temporal Variations: Secular Variation, Reversals, and Excursions

Temporal behavior includes secular variation, geomagnetic jerks, excursions, and full polarity reversals documented in stratigraphic records compiled by researchers like Keith Runcorn, Vine–Matthews–Morley seafloor studies, and paleomagnetic databases curated by NOAA and PANGAEA. Chronologies link reversals to geomagnetic polarity timescales developed by C. R. Scotese, W. Jason Morgan, and stratigraphers at Lamont–Doherty Earth Observatory. Excursions and reversals are studied via marine magnetic anomalies from expeditions on R/V JOIDES Resolution, HMS Challenger, and cores analyzed at British Antarctic Survey and Alfred Wegener Institute. Short-term phenomena are monitored by observatories within INTERMAGNET, and models of secular acceleration involve contributions from J. Bloxham, Nicolas Alekseevich],] and Christopher Finlay.

Measurement Methods and Instrumentation

Instrumentation spans fluxgate magnetometers, proton precession magnetometers, optically pumped magnetometers, superconducting quantum interference devices (SQUIDs), and satellite magnetometers developed by teams at GEOMAGIA, ESA, NASA Goddard Space Flight Center, JPL, JAXA, and ISRO. Ground surveys use magnetometers produced by firms like Geometrics and platforms including airborne surveys by USGS contractors, marine surveys aboard NOAA Ship Ronald H. Brown and drilling programs like IODP. Calibration standards are maintained by national metrology institutes such as NIST, PTB, and NPL. Laboratory techniques include rock magnetism analyses at University of Minnesota Paleomagnetism Laboratory and paleointensity methods refined at ETH Zurich and University of Tokyo.

Effects on Navigation, Atmosphere, and Biosphere

Geomagnetism impacts navigation systems used by mariners, aviators, and space missions maintained by International Civil Aviation Organization, IMO, and agencies like NASA and ESA; historical reliance on compasses influenced voyages by Ferdinand Magellan and Christopher Columbus. Geomagnetic storms driven by Solar flares and Coronal Mass Ejections disrupt satellites operated by Intelsat, Iridium Communications, and power grids managed by organizations such as National Grid (UK) and Federal Energy Regulatory Commission. Atmospheric coupling produces aurorae observed from stations like McMurdo Station and satellites such as IMAGE (satellite), while magnetoreception in animals is studied by biologists at Max Planck Institute for Ornithology, Cornell Lab of Ornithology, and University of Oxford.

Applications and Modeling in Geophysics

Applied geophysics uses geomagnetic models for mineral exploration by companies and surveys undertaken by Rio Tinto, BHP, and national geological surveys; tectonic reconstructions by Paleomap Project and hazard assessment by USGS integrate magnetic data. Numerical models are implemented in software frameworks developed at MIT, Stanford University, Imperial College London, and research programs at Institut de Physique du Globe de Paris. Space weather forecasting ensembles employ inputs from NOAA Space Weather Prediction Center, Met Office (UK), and private services like Spire Global. Ongoing collaborations across agencies including World Data Center for Geomagnetism, Kyoto, INTERMAGNET, International Association of Geomagnetism and Aeronomy, and universities ensure continuous improvement of models used in navigation, resource exploration, and scientific inquiry.

Category:Geophysics