Geomagnetism (science)

Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties.

A magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force).

It is approximately the field of a magnetic dipole tilted at an angle of 11 degrees with respect to the rotational axis—as if there were a bar magnet placed at that angle at the center of the Earth.

It is approximately the field of a magnetic dipole tilted at an angle of 11 degrees with respect to the rotational axis—as if there were a bar magnet placed at that angle at the center of the Earth.

The region above the ionosphere, and extending several tens of thousands of kilometers into space, is called the magnetosphere.

It is generally reported in nanoteslas (nT) or gauss, with 1 gauss = 100,000 nT.

Earth's magnetic field (also known as the geomagnetic field) is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun.

Earth's magnetic field (also known as the geomagnetic field) is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun.

Spherical harmonics can represent any scalar field (function of position) that satisfies certain properties.

Isogonic lines give the declination in signed degrees.

A Coriolis effect, caused by the overall planetary rotation, tends to organize the flow into rolls aligned along the north-south polar axis.[27][28]

Variations in the magnetic field strength have been correlated to rainfall variation within the tropics.[14]

[edit]Time dependence

[edit]Short-term variations


Background: a set of traces from magnetic observatories showing a magnetic storm in 2000.

The Magnetic North Pole wanders, fortunately slowly enough that the compass is useful for navigation.

The region above the ionosphere, and extending several tens of thousands of kilometers into space, is called the magnetosphere.

Information on declination for a region can be represented by a chart with isogonic lines (contour lines with each line representing a fixed declination).

[edit]Magnetic poles
Main articles: North Magnetic Pole, South Magnetic Pole, and Geomagnetic pole


The movement of Earth's North Magnetic Pole across the Canadian arctic, 1831–2001.

It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator.

The average magnetic field in the Earth's outer core was calculated to be 25 Gauss, 50 times stronger than the field at the surface.[29][30]

[edit]Numerical models


Computer simulation of the Earth's field in a normal period between reversals.[31]

This remanent magnetization, or remanence, can be acquired in more than one way.

A ship towing a magnetometer on the surface of the ocean can detect these stripes and infer the age of the ocean floor below.

It can be estimated by comparing the magnetic north/south heading on a compass with the direction of a celestial pole.

Variations in the magnetic field strength have been correlated to rainfall variation within the tropics.[14]

[edit]Time dependence

[edit]Short-term variations


Background: a set of traces from magnetic observatories showing a magnetic storm in 2000.

It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator.

~ 1:50,000).[36]

[edit]Crustal magnetic anomalies


A model of short-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies.[37]

Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped.

The declination or variation is the angle the needle would make with true north if it were constrained to lie in a horizontal plane (as in an ordinary compass).

Frequently, the Earth's magnetosphere is hit by solar flares causing geomagnetic storms, provoking displays of aurorae.

The past magnetic field is recorded mostly by iron oxides, such as magnetite, that have some form of ferrimagnetism or other magnetic ordering that allows the Earth's field to magnetize them.

For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind.

For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind.

These effects can be combined in an equation for the magnetic field only called the magnetic induction equation:


where u is the velocity of the fluid, B is the magnetic B-field; and η=1/σμ is the magnetic diffusivity with σ electrical conductivity and μ permeability.[27]