The amount of secular change in the earth’s magnetic field which occurs in 1 year. magnetic annual variation; the small systematic temporal variation in the earth’s magnetic field which occurs after the trend for secular change has been removed from the average monthly values.



Related Terms

ISOGONIC CHART

A chart showing magnetic variation with isogonic lines and the annual rate of change in variation with isoporic lines.

ASTATIC MAGNETOMETER

A magnetometer for determining the gradient of a magnetic field by measuring the difference in reading from two magnetometers placed at different positions.

OPTICALLY PUMPED MAGNETOMETER

A type of magnetometer that measures total magnetic field intensity by observation of the precession frequency of magnetic atoms, usually gaseous rubidium, cesium, or helium, which are magnetized by irradiation with circularly polarized light of a suitable wavelength.

ISOPORIC CHART

A chart with lines connecting points of equal annual rate of change of any magnetic element

ELECTRON-BEAM CHANNELING

The technique of transporting high-energy, high-current electron beams from an accelerator to a target through a region of high-pressure gas by creating a path through the gas where the gas density may be temporarily reduced; the gas may be ionized; or a current may flow whose magnetic field focuses the electron beam on the target.

FLUX GATE

A detector that gives an electric signal whose magnitude and phase are proportional to the magnitude and direction of the external magnetic field acting along its axis; used to indicate the direction of the terrestrial magnetic field.

VIBRATING NEEDLE

A magnetic needle used in compass adjustment to find the relative intensity of the horizontal components of the earth’s magnetic field and the magnetic field at the compass location. Also called HORIZONTAL FORCE INSTRUMENT.

MAGNET

A body which produces a magnetic field around itself. It has the property of attracting certain materials capable of being magnetized. A magnet occurring in nature is called a natural magnet in contrast with a man-made artificial magnet.

DEGAUSSING

Neutralization of the strength of the magnetic field of a vessel, using electric coils permanently installed in the vessel.

LINE OF FORCE

A line indicating the direction in which a force acts, as in a magnetic field

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