Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.

Possible links between long-term geomagnetic variations and whole-mantle convection processes

Abstract: The Earth's internal magnetic field varies on timescales of months to billions of years. The field is generated by convection in the liquid outer core, which in turn is influenced by the heat flowing from the core into the base of the overlying mantle. Much of the magnetic field's variation is thought to be stochastic, but over very long timescales, this variability may be related to changes in heat flow associated with mantle convection processes. Over the past 500 Myr, correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late Mesozoic era, beginning about 180 Myr ago. Simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability — such as occurred between the Middle Jurassic and Middle Cretaceous periods — may have been triggered by a decrease in core-mantle boundary heat flow either globally or in equatorial regions. This decrease in heat flow could have been linked to reduced mantle-plume-head production at the core-mantle boundary, an episode of true polar wander, or a combination of the two.

Physics of the upper polar atmosphere

Abstract: 1. The Sun as a radiation source.- 1.1 General about the Sun .- 1.2 The solar atmosphere.- 1.3 The electromagnetic radiation from the Sun .- 1.4 Planck's radiation law.- 1.5 The greenhouse effect.- 1.6 Radiowave emissions from the Sun.-1.7 The sunspots - Solar cycle.-1.8 The electromagnetic radiation from the disturbed Sun.- 1.9 Particle emissions from the quiet Sun.-1.10 Fluid flow in a nozzle.- 1.11 The solar wind equation.- 1.12 The frozen-in field concept 1.13 The garden hose effect.- 1.14 Exercises.- 2. The atmosphere of the Earth 2.1 Nomenclature.- 2.2 The temperature structure of the atmosphere.- 2.3 Atmospheric drag on satellites.- 2.4 The atmosphere as an ideal gas.- 2.5 The exosphere.- 2.6 Height-dependent temperature.- 2.7 The adiabatic lapse rate.- 2.8 Diffusion.- 2.9 The equation of motion of the neutral gas.- 2.10 The geostrophic and thermal winds.- 2.11 The wind systems of the upper atmosphere.- 2.12 Observations of the neutral wind.- 2.13 Collisions between particles.- 2.14 Collisions in gases with different temperatures.- 2.15 Drag effects.- 2.16 Thermospheric neutral winds.- 2.17 The E-region winds.- 2.18 Observations of E-region neutral winds.- 2.19 The vertical motion.- 2.20 Exercises.- 3. The Earth's magnetic field and magnetosphere.- 3.1 An historical introduction.- 3.2 Description of the Earth's magnetic field.- 3.3 Mathematical representation of the Earth's magnetic system.- 3.4 Secular variations in the Earth's magnetic field.- 3.5 Tracing the magnetic field lines.- 3.6 E-field mapping along conducting magnetic field lines.- 3.7 The source of the magnetic field of the Earth.- 3.8 The unipolar inductor.- 3.9 The magnetic field away from the Earth.- 3.10 The magnetic tail.- 3.11 Magnetic field merging.- 3.12 Effects of the magnetic force.- 3.13 The energy flux into the magnetosphere.-3.14 Some aspects of the energy balance.- 3.15 Magnetic field convection.- 3.16 High-latitude convection patterns and field-aligned currents 3.17 Exercises .- 4. The ionosphere.- 4.1 The production of ionization by solar radiation.- 4.2 The ionization profile of the upper atmosphere.- 4.3 The Chapman ionization profile.- 4.4 The recombination process.- 4.5 The O+ dominant ionosphere.- 4.6 Ambipolar diffusion.- 4.7 Multicomponent topside ionosphere.- 4.8 Diffusion in the presence of a magnetic field.- 4.9 The E-layer ionization and recombination.- 4.10 The time constant of the recombination process.-4.11 The D-region ionization and recombination.- 4.12 Equatorial fountain effect.- 4.13 Ferraro's theorem.- 4.14 The magnetospheric convection close to the Earth 4.15 Exercises .-5 Currents in the ionosphere.- 5.1 The steady-state approach.- 5.2 Rotation of the ion velocity by height in the ionosphere.- 5.3 The current density in the ionosphere.- 5.4 Height-dependent currents and heating rates.- 5.5 Heating due to collisions.- 5.6 Heating of an oscillating electric field.- 5.7 Currents due to gravity and diffusion.- 5.8 Exercises.- 6. Magnetic fluctuations in response to height-integrated currents.- 6.1 Height-integrated currents and conductance.- 6.2 Magnetic field fluctuations from auroral currents.- 6.3 Equivalent current systems.- 6.4 Equivalent currents at different latitudes.- 6.5 The Sq current system.- 6.6 Mapping of E-fields in the ionosphere.- 6.7 Polarization fields around an auroral arc.- 6.8 Currents related to an auroral arc.- 6.9 Exercises.- 7 The aurora.- 7.1 An historical introduction.- 7.2 The height of the aurora.- 7.3 The occurrence frequency of the aurora.- 7.4 The global distribution of the aurora.- 7.5 The auroral appearance.- 7.6 Auroral particles.- 7.7 Precipitation patterns of auroral particles.- 7.8 The energy deposition profiles of auroral particles.- 7.9 Deriving energy spectra from electron density profiles.- 7.10 Excitation processes in the aurora.-7.11 The quenching process.- 7.12 The proton aurora.- 7.13 Exercises References Symbols Index.

Storm sudden commencement events and the associated geomagnetically induced current risks to ground-based systems at low-latitude and midlatitude locations

Abstract: [1] Large impulsive geomagnetic field disturbances from auroral current systems have always been well understood as a concern for power grids in close proximity to these disturbance regions, predominantly at high-latitude locations. Magnetospheric shocks (SSCs) due to large-scale interplanetary pressure pulses are familiar from a geomagnetic disturbance perspective but have not been understood in the context as a potential driver for large geomagnetically induced currents (GICs). Observational evidence and analysis contained in this paper illustrate such events are capable of producing large geoelectric fields and associated GIC risks at any latitude, even equatorial locations. A large SSC disturbance on 24 March 1991 produced some of the largest GICs ever measured in the United States at midlatitude locations. The analysis methods and understanding of electromagnetic coupling processes at that time were unable to fully explain these observations. Electrojet-driven disturbances common at high-latitude locations during geomagnetic substorms cause large amplitude variations in locally observed B field, while SSC events are characterized as low-amplitude B field disturbance events. Disturbance amplitude only accounts for part of the electromagnetic coupling process. The attribute of spectral content of the disturbance is equally important and heretofore had not been well understood and was not well measured unless high-cadence observations were conducted. The deep-earth ground conductivity also provides an important enabling role at higher frequencies. Deep-earth ground response to geomagnetic field disturbances is highly frequency-dependent. Therefore for nearly all ground conditions the higher the spectral content of the incident magnetic field disturbance, the higher the relative geoelectric field response.