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Topic: Geomagnetic field

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North Pole

Dipole moment

Polar drift

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Timeline of events leading to the American Civil War

2003

	Earth's magnetic field - Wikipedia, the free encyclopedia
		Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole and the other near the geographic south pole.
		The cause of the field is probably explained by dynamo theory.
		The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated spins of electrons and nuclei within iron atoms.
	en.wikipedia.org /wiki/Earth's_magnetic_field (1509 words)

	Geomagnetic reversal - Wikipedia, the free encyclopedia
		A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged.
		Since the field is stable in either the present North-South orientation or a reversed orientation, they propose that when the field recovers from such a disruption it spontaneously chooses one or the other state, such that a recovery is seen as a reversal in about half of all cases.
		A possible explanation is that the solar wind may induce a sufficient magnetic field in the Earth's ionosphere to shield energetic particles even in the absence of the Earth's normal magnetic field [1].
	en.wikipedia.org /wiki/Geomagnetic_reversal (1182 words)

	Magnetic field - Wikipedia, the free encyclopedia
		A changing electric field can be caused by the movement of an electrically charged object, as in an electric current; or a combination of the orbit of an electron around an atom and the spin of electrons themselves, as in a permanent magnet.
		Thus, according to Einstein's field transformation equations (that is, the Lorentz transformation of the field from a proper reference frame to a non-moving reference frame), part of it is manifested as an electric field component.
		It is a response of a medium to the presence of a magnetic field.
	en.wikipedia.org /wiki/Magnetic_field (3043 words)

	Geomagnetism: The Magnetic Field of the Earth
		The geomagnetic field model is also vital to various kinds of magnetic surveys, such as those used in mineral exploration and the mapping of hazardous earthquake faults.
		The geomagnetic reference model is the basis for establishing the declination and its variation across the surface of the globe.
		The influence of this distortion of the geomagnetic field is quite small near Earth's surface (except during solar eruptions associated with sunspots) and becomes larger with increasing distance from Earth.
	www.nationalatlas.gov /articles/geology/a_geomag.html (677 words)

	USGS National Geomagnetism Program \| Intro to Geomag
		The dipolar part of the field is actually tilted by approximately 11° with respect to the rotational axis, and there are additional, non-dipolar ingredients in the geomagnetic field, all of which, when added together, are the total surficial field in all of its complex detail.
		The geographic variation of declination is indicative of the field's complexity, with declination contours converging at the geomagnetic poles.
		The magnetosphere is the outer part of the Earth's magnetic field, a region in the near-Earth space environment where the shape and behavior of the geomagnetic field is governed by the Sun.
	geomag.usgs.gov /intro.php (2887 words)

	Geomagnetic field decay - CreationWiki
		The theory is that as lava cools, the magnetic fields of the atoms align with the Earth's field, that as the sea floor spreads a record of Earth's past fields is preserved.
		The way the theory is illustrated is with present magnetic field direction and reverse magnetic field direction in nice neat strips across the ocean floor, as produced by the theory.
		The existence of the magnetic field of Mercury, since the field's source is a decaying current in its core and it is not related to spin.
	www.creationwiki.net /index.php?title=Geomagnetic_field_decay (1159 words)

	Remote Sensing of Geomagnetic Field and Applications to Climate Prediction
		The exact mechanism for the observed close relationship between global geomagnetic field and the tropospheric weather patterns is not clear.
		Therefore, atmospheric circulation patterns leave signature on the geomagnetic field lines whose global variations can be easily monitored by satellite borne sensors and thus assist in weather and climate prediction.
		Field aligned currents in discrete auroral arcs are visible manifestations of atmospheric vertical mixing coupled to solar wind pumping of negative space charges downwards accompanied by simultaneous upward transport of terrestrial positive ions.
	www.geocities.com /CapeCanaveral/Lab/5833/geomag/geoclim.html (3544 words)

	Background: Magnetic field models
		The Earth's real magnetic field is the sum of several contributions including the main (core) and crustal (anomaly) fields (also referred to as the geomagnetic field), and the external source (magnetospheric) fields.
		The Earth's magnetic field is a sum of several contributions including the main (core) field, the crustal (anomaly) field, and the external source (magnetospheric) fields.
		The model is capable of accurately representing the dayside magnetic field at geosynchronous orbit for all magnetic conditions and the nightside field for non-substorm conditions.
	www.spenvis.oma.be /spenvis/help/background/magfield/magfield.html (1646 words)

	Rouse, I. E. --- Paleomagnetism II
		The actual amount of energy necessary to maintain the geomagnetic field is dependent on the model as well as the conditions in the core, which are not well known.
		The determination of the direction and intensity of the paleomagnetic field of the earth necessitates the careful measurement, using a magnetometer, of the direction and magnitude of the magnetic moment or field of a cylindrical sample of material having a volume of a few cubic centimeters.
		Reversals of the geomagnetic field, magnetostratigraphic, and relative magnitude of paleosecular variation in the phanerozoic.
	www.grisda.org /origins/10066.htm (7922 words)

	Background: Dipole approximations of the geomagnetic field
		In order to approximate the geomagnetic field with a dipole which is not necessarily located at the centre of the Earth, the criterion to be used to judge the best fit to the observed field has to be defined.
		Because of the displacement of the eccentric pole away from the Earth's centre the eccentric dipole axis and associated magnetic field, in particular, are not perpendicular to the surface at the axial poles.
		At these points there is enough curvature of the dipole field lines away from the eccentric dipole axis to compensate for the small angle made by the axis with the Earth's surface and thus to bring the field lines perpendicular to the surface (see figure 2).
	www.spenvis.oma.be /spenvis/help/background/magfield/cd.html (1953 words)

	Magnetic Field - Declination Component for the Epoch 1995.0
		This field is what causes a compass needle to point north, and it can be seen in the aurora that is sometimes visible at high latitudes.
		Geomagnetic storms (rapid variations in the magnetic field) pose significant hazards to satellites, electrical power distribution systems, radio communications, and geophysical surveys.
		Scientists at the USGS and at other agencies around the world compile data on the magnetic field in five year increments, which is then used to produce a model of the magnetic field called the International Geomagnetic Reference Field (IGRF).
	nationalatlas.gov /mld/dmfcntl.html (652 words)

	Ships shed light on geomagnetic field (May 2006) - News - PhysicsWeb (Site not responding. Last check: 2007-10-31)
		Such geomagnetic flips are thought to occur once every 300,000 years or so, with the actual reversal taking thousands of years to complete.
		However, it is not known whether a decline in the Earth's magnetic field strength is inevitable.
		These results show that the magnetic field strength was relatively stable from 1590 to 1840, and has steadily fallen by about 5% each century since then (see figure).
	physicsweb.org /articles/news/10/5/7/1?rss=1.0 (444 words)

	cat1aa
		The Earth's magnetic field is described by seven parameters.To measure the Earth's magnetism in any place, we must measure the direction and intensity of the field.
		The intensity of the total field (F) is described by the horizontal component (H), vertical component (Z), and the north (X) and east (Y) components of the horizontal intensity.
		The geomagnetic field measured at any point on the Earth's surface is a combination of several magnetic fields generated by various sources.
	www.wdcb.ru /stp/cat1GEO.html (1641 words)

	USGS Geomagnetic Field Calculator
		Model Types For most users interested in the present geomagnetic field the IGRF-2000 model will be of most use, it being a reasonably accurate depiction of the field everywhere on the Earth?s surface for the years 2000-2005.
		On the other hand, the DGRF (Definitive Geomagnetic Reference Field) models are ?post-dictive?, in that they are based on data collected in the past, over a certain duration of time, and are intended to represent the field in the past, over the same duration of time.
		Since the magnetic field is extremely complicated, in both space and time, magnetic-field models are, by practical necessity, something of an approximation of the actual magnetic field.
	gcmd.gsfc.nasa.gov /records/Geomag_Field_Calc.html (563 words)

	Slide 2
		The geomagnetic field measures approximately 0.00004 Tesla (Hecht, 2003) and that is rather weak compared to the magnetic force (~0.3 to 0.4 Tesla) of a large ferromagnetic bar (2003).
		The field lines of a bar magnet always point from north to south as does a compass needle; conventionally, the magnetic North Pole is called 'north' because of its geographic location.
		The motion of the fluid is thought to be complicated by the differential rotational movement of Earth's layers, by a resistivity at the boundaries and the Coreolis effect, a torque exerted by Earth's rotational movement.
	ffden-2.phys.uaf.edu /104_spring2004.web.dir/Carla_Tomsich/Slide2.htm (1125 words)

	Psi and Geomagnetic Effects
		The geomagnetic activity levels of the earth are measured by the fluctuation of the planets magnetic field in a unit called Gauss.
		The activity of the earth's magnetic field is caused by internal as well as external factors, such as solar radiation radio broadcasts.
		The earth's magnetic field is measured around the planet by many observatories, the data retrieved is processed and turned in to measurement indices.
	www.fpc.edu /pages/Academics/behave/psych/web96-1.htm (1634 words)

	PERCY SEYMOUR
		We've found out that the strength of the field that we've calculated is in keeping with the strength of the field measured by other methods, such as the Zeeman effect, which is how the magnetic field affects the light of the Sun.
		This process and the differential rotation of the Sun are the astrophysical processes that "prepare" the solar magnetic field to respond to the resonant tidal tug of the planets.
		This reversal of the Sun's magnetic field is called the Sun's magnetic cycle, which is approximately 22 years long, twice the duration of the eleven-year solar/sunspot cycle.
	www.tmgnow.com /repository/solar/percyseymour1.html (6777 words)

	Geodynamo
		In addition, paleomagnetic records show that the dipole polarity of the geomagnetic field has reversed many times in the past, the mean time between reversals being roughly 200,000 years with individual reversal events taking only a couple thousand years.
		The simulated magnetic field has an intensity and a dipole dominated structure that is very similar to the Earth's (Figure 2) and a westward drift of the non-dipolar structures of the field at the surface that is essentially the same as the 0.2 degrees/year measured on the Earth.
		A transition occurs at the core-mantle boundary from the intense, complicated field structure in the fluid core, where the field is generated, to the smooth, potential field structure outside the core.
	www.es.ucsc.edu /~glatz/geodynamo.html (1233 words)

	The Earth’s Magnetic Field is Still Losing Energy
		The field of the earth is indeed close to being that of a dipole, though the dipole’s axis tilts about 11.5° away from the earth’s rotational axis.
		Although magnetic fields and energies also exist in the core as well as outside it, observations of the field outside the core cannot determine the field in the core.
		Decay of the earth’s magnetic field and the geochronological implications.
	www.creationresearch.org /crsq/articles/39/39_1/GeoMag.htm (5738 words)

	USGS National Geomagnetism Program \| Home \| Models
		The models are expressed in two ways, in the form of charts, showing the various magnetic-field components at the surface, and in form of calculator which gives the field components at a chosen time and geographical location.
		For most users interested in the present geomagnetic field the IGRF-2000 model will be of most use, it being a reasonably accurate depiction of the field everywhere on the Earth’s surface for the years 2000-2005.
		IGRF (International Geomagnetic Reference Field) models are ‘pre-dictive’, in that they are based on data collected in the recent past, preceding their construction, and are intended to represent the field in the near future, following their construction.
	geomag.usgs.gov /models (552 words)

	International Geomagnetic Reference Field MPEG (Site not responding. Last check: 2007-10-31)
		The magnetic fields are calculated for an epoch of 1994.0.
		The spherical harmonic coefficients of the International Geomagnetic Reference Field, IGRF 1991, data set IGRF90.dat for 1990.0 and the projected data set IGRF90s.dat, for 1995.0 were interpolated to 1994.0.
		The IGRF model does not show effects on the magnetic field near the earth due to "external" processes such as the solar wind or ionospheric currents.
	powerweb.grc.nasa.gov /pvsee/info/movies/igrf94.html (339 words)

	Geomagnetic Field
		The geomagnetic field of the earth is very similar to that of a large bar magnet placed at the center of the Earth, with its south end oriented toward the north magnetic pole.
		The field is dipolar, vertically downward at the north magnetic pole, vertically upward at the south magnetic pole, and horizontal at the (magnetic) equator.
		In the United States, it is acceptable for the purposes of simple modeling to assume that a field declination of about 60 degrees has a strength of 55,000 gammas.
	www.freewebtown.com /geophysics2/geomag.html (494 words)

	WHEN NORTH GOES SOUTH: Three-Dimensional Simulation of Geomagnetic Field Reversal
		Between the mantle and the inner core is a fluid layer, the outer core.
		Contrary to what anyone guessed till now, the model shows that in the inner core the magnetic field has an opposite polarity from the outer core, and this stabilizes the field against a tendency to reverse more frequently.
		The left hemisphere shows that the field penetrating the inner core is opposed in polarity to the outer core, a feature completely unanticipated by theory.
	www.psc.edu /science/Glatzmaier/glatzmaier.html (1130 words)

	Geomagnetism
		The Earth's magnetic field (or geomagnetic field) is an ever-changing phenomenon that influences human activity and the natural world in a myriad of ways.
		The geomagnetic field changes from place to place, and on time scales ranging from seconds to decades to eons.
		The geomagnetic field, along with its associated phenomena, can both assist and degrade navigation and surveying techniques; it can impede geophysical exploration; it can disrupt electric power utilities, and pipeline operations; and it can influence modern communications systems, spacecraft, and more.
	gsc.nrcan.gc.ca /geomag/index_e.php (143 words)

	CPCP \| Simulation of Earth's Geomagnetic Field
		Why does the field change its polarity at irregular intervals separated by intervals of order a million years.
		It has long been realized that the field must be due to electric currents flowing in the electrically conducting core.
		Becasue of the statistical indifference of the field to the sense of polarity it seems certain that these currents are driven by self-excited dynamo action.
	www.igpp.ucla.edu /cpcp/field.html (357 words)

	Nigeria Journal of Pure and Applied Physics - Vol. 3, No. 1 (2004)
		This study investigated the variation of the ranges of the geomagnetic field elements H, D, Z at seasonal and yearly levels.
		The relationship of the geomagnetic field ranges with the solar cycle is also examined.
		During disturbed condition, the d-season range of Z is greater than range of H. The solar cycle influence the geomagnetic field at the subauroral region must be directional.
	www.ajol.info /viewarticle.php?id=20443 (291 words)

	Glossary: Geomagnetic field
		The geomagnetic field is the magnetic force field that surrounds the Earth.
		It is attributed to the combined effects of the planetary rotation and the movement of molten iron in the Earth's' core.
		Some birds (particularly migratory species) and other animals seem to rely on the geomagnetic field to orient themselves.
	www.greenfacts.org /glossary/ghi/geomagnetic-field.htm (114 words)

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