176:
210:. The direction and intensity of the dipole change over time. Over the last two centuries the dipole strength has been decreasing at a rate of about 6.3% per century. At this rate of decrease, the field would reach zero in about 1600 years. However, this strength is about average for the last 7 thousand years, and the current rate of change is not unusual.
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at a rate of about 0.2 degrees per year. This drift is not the same everywhere and has varied over time. The globally averaged drift has been westward since about 1400 AD but eastward between about 1000 AD and 1400 AD.
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or daily variations in currents. Changes over time scales of a year or more mostly reflect changes in the Earth's interior, particularly the iron-rich
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part, like the field around a bar magnet, and a non-dipolar part. The dipolar part dominates the geomagnetic field and determines the direction of the
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Dumberry, Mathieu; Finlay, Christopher C. (2007). "Eastward and westward drift of the Earth's magnetic field for the last three millennia".
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The geomagnetic field changes on time scales from milliseconds to millions of years. Shorter time scales mostly arise from currents in the
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Jackson, Andrew; Jonkers, Art R. T.; Walker, Matthew R. (2000). "Four centuries of
Geomagnetic Secular Variation from Historical Records".
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Secular variation can be observed in measurements at magnetic observatories, some of which have been operating for hundreds of years (the
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is observed to vary over tens of degrees. A movie on the right shows how global declinations have changed over the last few centuries.
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Changes that predate magnetic observatories are recorded in archaeological and geological materials. Such changes are referred to as
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The
Levantine Iron Age anomaly was a fast and spatially localized geomagnetic positive anomaly which took place in the
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Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020, according to three models.
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234:. The records typically include long periods of small change with occasional large changes reflecting
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To analyze global patterns of change in the geomagnetic field, geophysicists fit the field data to a
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Philosophical
Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
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475:(2007). "Dipole Moment Variation". In Gubbins, David; Herrero-Bervera, Emilio (eds.).
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Fournier, Alexandre; Aubert, Julien; Lesur, Vincent; Thébault, Erwan (December 2021).
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on time scales of about a year or more. These changes mostly reflect changes in the
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The
Magnetic Field of the Earth: Paleomagnetism, the Core, and the Deep Mantle
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Estimated declination contours by year, 1590 to 1990 (click to see variation).
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A prominent feature in the non-dipolar part of the secular variation is a
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Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996).
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Rivera, Pablo; Pavón-Carrasco, F. Javier; Osete, María Luisa (2023).
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304:"Physics-based secular variation candidate models for the IGRF"
404:"Modeling geomagnetic spikes: the Levantine Iron Age anomaly"
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202:). The terms in this expansion can be divided into a
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McElhinny, Michael W.; McFadden, Phillip L. (1998).
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30:, while more rapid changes mostly originate in the
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611:. International Geophysics Series. Vol. 63.
16:Short-term changes in the Earth's magnetic field
477:Encyclopedia of Geomagnetism and Paleomagnetism
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67:, the secular variation is the amortized time
249:, with maxima at about 950, 750 and 500 BCE.
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200:International Geomagnetic Reference Field
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290:Merrill, McElhinny & McFadden 1996
148:{\displaystyle {\ddot {\mathbf {B} }}}
668:Paleomagnetic Principles and Practice
586:Paleomagnetism: Continents and Oceans
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352:
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117:{\displaystyle {\dot {\mathbf {B} }}}
7:
57:. These changes are referred to as
49:, and some changes can be traced to
509:Earth and Planetary Science Letters
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343:Jackson, Jonkers & Walker 2000
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228:paleomagnetic secular variation
222:Paleomagnetic secular variation
638:University of California Press
1:
20:Geomagnetic secular variation
633:Essentials of Paleomagnetism
489:10.1007/978-1-4020-4423-6_67
232:paleosecular variation (PSV)
86:{\displaystyle \mathbf {B} }
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530:10.1016/j.epsl.2006.11.026
457:Canadian Geological Survey
429:10.1186/s40623-023-01880-x
379:Dumberry & Finlay 2007
329:10.1186/s40623-021-01507-z
124:. The second derivative,
22:refers to changes in the
408:Earth, Planets and Space
308:Earth, Planets and Space
522:2007E&PSL.254..146D
420:2023EP&S...75..133R
320:2021EP&S...73..190F
561:10.1098/rsta.2000.0569
236:geomagnetic excursions
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71:of the magnetic field
24:Earth's magnetic field
240:geomagnetic reversals
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666:Tauxe, Lisa (1998).
630:Tauxe, Lisa (2010).
483:. pp. 159–161.
473:Constable, Catherine
189:magnetic declination
157:secular acceleration
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97:
75:
553:2000RSPTA.358..957J
449:"Secular variation"
196:spherical harmonic
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51:geomagnetic storms
647:978-0-520-26031-3
547:(1768): 957–990.
498:978-1-4020-3992-8
264:Secular variation
208:geomagnetic poles
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60:secular variation
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650:. Archived from
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163:Recent changes
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700:Geomagnetism
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656:. Retrieved
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441:References
390:Tauxe 1998
314:(1): 190.
69:derivative
63:. In most
43:ionosphere
32:ionosphere
140:¨
109:˙
694:Category
577:40510741
463:July 18,
357:CGS 2011
253:See also
569:2666741
549:Bibcode
518:Bibcode
416:Bibcode
414:(133).
392:, Ch. 1
316:Bibcode
292:, Ch. 2
204:dipolar
155:is the
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672:Kluwer
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495:
459:. 2011
247:Levant
65:models
573:S2CID
565:JSTOR
270:Notes
676:ISBN
642:ISBN
617:ISBN
594:ISBN
493:ISBN
465:2011
238:and
55:core
45:and
557:doi
545:358
526:doi
514:254
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324:doi
230:or
34:or
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412:75
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349:^
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278:^
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136:B
105:B
80:B
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