The steady part of the secular variation of the Earth's magnetic field

1992 ◽  
Vol 97 (B13) ◽  
pp. 19565 ◽  
Author(s):  
Jeremy Bloxham
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Earth’S Magnetic Field ◽  
Earth's Magnetic Field

The westward drift of the Earth's magnetic field

1950 ◽  
Vol 243 (859) ◽  
pp. 67-92 ◽  
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Outer Part ◽  
Earth’S Magnetic Field ◽  
Dynamo Theory ◽  
The Core ◽  
The Earth ◽  
Earth's Magnetic Field ◽  
Harmonic Analyses ◽  
Westward Drift

The westward drift of the non-dipole part of the earth’s magnetic field and of its secular variation is investigated for the period 1907-45 and the uncertainty of the results discussed. It is found that a real drift exists having an angular velocity which is independent of latitude. For the non-dipole field the rate of drift is 0.18 ± 0-015°/year, that for the secular variation is 0.32 ±0-067°/year. The results are confirmed by a study of harmonic analyses made between 1829 and 1945. The drift is explained as a consequence of the dynamo theory of the origin of the earth’s field. This theory required the outer part of the core to rotate less rapidly than the inner part. As a result of electromagnetic forces the solid mantle of the earth is coupled to the core as a whole, and the outer part of the core therefore travels westward relative to the mantle, carrying the minor features of the field with it.

Secular variation of the Earth's magnetic field revealed by Mexican Geomagnetic Repeat Stations during the last two centuries

2021 ◽  
pp. 103652
Author(s):  
Avto Goguitchaichvili ◽  
Esteban Hernández ◽  
Rafael García ◽  
Vadim Kravchinsky ◽  
Rubén Cejudo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Earth’S Magnetic Field ◽  
Earth's Magnetic Field

scholarly journals Multipole Analysis. II. Geomagnetic Secular Variation

1969 ◽  
Vol 22 (4) ◽  
pp. 481 ◽  
Author(s):  
RW James
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Time Trends ◽  
Earth’S Magnetic Field ◽  
Geomagnetic Secular Variation ◽  
Rates Of Change ◽  
Multipole Analysis ◽  
Earth's Magnetic Field

The method of multipole analysis described in Part I is applied to the Earth's magnetic field for various epochs between 1845 and 1965, allowing the geomagnetic secular variation to be illustrated by time trends in the multipole parameters. The rates of change of the multipole parameters are used to separate the secular variation into non.drifting, meridional drifting, and longitudinal drifting components, which are discussed in detail for the epoch 1965.

Paleomagnetism of the Abitibi dyke swarm, southern Superior Province, and implications for the Logan Loop

1993 ◽  
Vol 30 (9) ◽  
pp. 1886-1897 ◽  
Author(s):  
Richard E. Ernst ◽  
Kenneth L. Buchan
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Dyke Swarm ◽  
Earth’S Magnetic Field ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Earth's Magnetic Field ◽  
Reversed Polarity ◽  
Magma Pulses ◽  
Middle Proterozoic

The trace of the Middle Proterozoic Logan Loop of the North American apparent polar wander path is controversial. The older 1270–1110 Ma limb of the loop is poorly constrained, while the depth of the loop, based on the 1110–1080 Ma Keweenawan data of the younger limb, is thought by some to be largely an artifact of reversal asymmetry in the Earth's magnetic field. Paleomagnetism of the 1141 Ma Abitibi mafic dyke swarm is one of the keys to constraining the geometry of the Logan Loop.Unfortunately, previous paleomagnetic studies failed to distinguish dykes of the northeast-trending Middle Proterozoic olivine-bearing Abitibi swarm from subparallel Early Proterozoic olivine-free Biscotasing (formerly Preissac) dykes, and hence paleomagnetic poles determined in these studies should no longer be used. In the present study, sampling of eight Abitibi dykes has identified 23 normally magnetized sites in four dykes and, for the first time, five reversely magnetized sites in three dykes. One of the normally magnetized sites corresponds to the locality for which a high-precision U–Pb age was previously reported. A baked contact test establishes that the characteristic remanence of one normally magnetized dyke is primary. In addition, sites along individual dykes exhibit much smaller secular variation than is observed between dykes, indicating that the remanences of the other dykes are also primary. One of the normally magnetized dykes, the 700 km long Great Abitibi dyke, exhibits two primary directions that correspond to two geochemically distinct magma pulses. The five normally magnetized units, which consist of four separate dykes plus the second pulse of the Great Abitibi dyke, yield a well-defined mean paleomagnetic pole at 42.8°N, 151.5°W, dm = 16.3°, dp = 12.5°. It falls close to the reversely magnetized poles from the Keweenawan Track and establishes a minimum depth for the Logan Loop of about 40°. The reversed-polarity data from three other dykes are more scattered and may not average out secular variation. Hence, the present study is inconclusive regarding asymmetry of the Earth's magnetic field at 1141 Ma, even though a mean pole based on combined normal-and reversed-polarity dykes is indistinguishable from that based on normal-polarity dykes alone.

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