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Section G G index 101-109 of 425 terms
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geological era—Same as geologic era.
geomagnetic coordinates—A system of spherical coordinates based on the best fit of a centered dipole to the actual magnetic field of the earth. The field due to an earth-centered magnetic dipole is given by the first three terms of the spherical harmonic expression of the IGRF (or DGRF) model.
geomagnetic equator—A great circle on the earth's surface that is everywhere equidistant from the geomagnetic poles, that is, the equator in the system of geomagnetic coordinates. See aclinic line.
geomagnetic latitude—A coordinate used in geomagnetism bearing the same relation to the geomagnetic dipole equator as geographic latitude does to the geographic equator. When meridional variations in phenomena closely related to the earth's magnetic field are plotted according to geomagnetic rather than geographic latitude, more clear-cut relations are usually depicted. Cosmic ray intensities and auroral frequencies are examples of quantities best studied as functions of this type of latitude.
Campbell, W. H., 1997: Introduction to Geomagnetic Fields, Cambridge Univ. Press, p. 32.
geomagnetic meridian—A great circle of the earth through the geomagnetic poles.
geomagnetic pole—A pole in the geomagnetic system of coordinates. Compare magnetic dipole.
geomagnetic storm—See magnetic storm.
geomagnetism—1. (Also called terrestrial magnetism, geomagnetic field.) The earth's magnetic field or the geophysical phenomena caused or affected by this field. 2. The scientific study of the earth's magnetic field, including its variation in space and time, and its relation to other geophysical phenomena (e.g., aurora). Geomagnetism belongs to the same family of earth sciences as geodesy and geomorphology.
geometric mean—For n positive numbers, the positive nth root of their product; that is, for the set of positive numbers x1, x2, . . ., xn, the geometric mean is the quantity (x1x2 · · · xn)1/n. Compare arithmetic mean.
geometric optics—The application of ray tracing to explain scattering and refractive effects by particles that are very large compared with the wavelength of the radiation. Geometric optics provides useful explanations for atmospheric features such as rainbows, halos, and many other ice crystal optical displays.
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