scholarly journals Possible consequences of a dwindling geomagnetic field

1971 ◽  
Vol 2 (3) ◽  
pp. 46
Author(s):  
I.K. Crain
Keyword(s):  
Geomagnetic Field ◽  
Dipole Field

Recently, Facer (1971) has discussed the problem of the dwindling of the geomagnetic field, and estimated that in 810 years (AD 2781) the dipole and non-dipole fields will be roughly equal and that in 1931 years (AD 3902) the dipole field will be essentially zero. Various authors (Crain and Crain, 1970; Cox, 1968; Parker, 1969) have suggested that these conditions are highly favourable for the production of geomagnetic reversals.

scholarly journals Features of the next reversal of the geomagnetic field

2021 ◽  
pp. 131-140
Author(s):  
В.В. Кузнецов
Keyword(s):  
Geomagnetic Field ◽  
Dipole Field ◽  
Total Field

В статье обсуждаются возможность проявления очередной инверсии геомагнитного поля (ГМП) и его некоторые особенности. Дипольное поле (ДП) приблизится к нулевой отметке, которую достигнет примерно в 3500 году. С 1500 года, на фоне понижения ДП происходит рост октупольного и квадрупольного компонент ГМП и их суммы (О+К). ДП, согласно нашей модели геомагнетизма, после прохождения нулевой отметки начнет расти с обратным знаком и противодействовать (О+К) полю, понижая его уровень до нуля. В этот момент (≈ 6000 год) поле (N) будет иметь минимальную величину. Затем начнется рост ДП обратного значения (R). Инверсия закончится при достижении этим полем устойчивой величины. The possibility of a new reversal of the geomagnetic field (GMF) and some of its features are discussed. In 3500 the dipole field (DF) will become near zero. Since 1500, along with the decrease of DF, there has been an increase of the octupole and quadrupole components of the GMF as well as their sum (O+Q). According to our model of geomagnetism, after passing the zero the reversing DF will start its rise counteracting the (O+Q) field and lowering its value to zero. In about 6000 the total field DF+O+Q (N) will be minimum. After DF reaches a stable value the reversal will complete.

New technique to diagnose the geomagnetic field based on the single circular current loop model

2020 ◽  
Author(s):  
Zhaojin Rong ◽  
Yong Wei ◽  
Wenyao Xu ◽  
Dali Kong ◽  
Jun Cui ◽  
...  
Keyword(s):  
Electric Current ◽  
Geomagnetic Field ◽  
Dipole Field ◽  
New Technique ◽  
Current Loop ◽  
Loop Model ◽  
Effective Technique ◽  
Circular Current ◽  
Planetary Magnetism ◽  
Geomagnetic Dipole

<p>A quick and effective technique is developed to diagnose the geomagnetic dipole field based on an unstrained single circular current loop model. In comparsion with previous studies, this technique is able to separate and solve the loop parameters successively. With this technique, one can search the optimum full loop parameters quickly, including the location of loop center, the loop orientation, the loop radius, and the electric current carried by the loop, which can roughly indicate the locations, sizes, orientations of the interior current sources. The technique tests and applications demonstrate that this technique is effective and applicable. This technique could be applied widely in the fields of geomagnetism, planetary magnetism and palaeomagnetism. The further applications and constrains are discussed and cautioned.</p>

Geophysical Studies of North African Cenozoic Volcanic Areas: III. Garian, Libya

1975 ◽  
Vol 12 (8) ◽  
pp. 1264-1271 ◽  
Author(s):  
J. M. Ade-Hall ◽  
Susann Gerstein ◽  
Robert E. Gerstein ◽  
Peter H. Reynolds ◽  
P. Dagley ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Field Direction ◽  
Dipole Field ◽  
Plate Motion ◽  
Paleomagnetic Data ◽  
North African ◽  
Axial Dipole ◽  
Repeated Sampling ◽  
Absolute Age ◽  
E 32

Paleomagnetic and K/Ar whole rock absolute age data are described for material from the Garian area of Libya, centered at 13°E, 32°N. Within-unit cleaned paleomagnetic directions from the essentially unaltered lavas are very well defined and can almost certainly be taken as reliable measurements of the geomagnetic field direction during the initial cooling of each flow. However, the distributions of mean direction, from which the effect of repeated sampling of the field at one time has been removed, does not suggest that a reversing axial dipole field has been recorded in a representative manner. Both N and R groups of directions are azimuthally elongated, and the average poles for the N and R groups differ by 21°, or four times the 95% level uncertainty for each average pole. A number of possible physical explanations for the paleomagnetic results are discussed. The conventional overall average pole at 88°N, 123°E, δp: 3°, δm: 7 °does not differ significantly from the geographic pole, a result which agrees closely with that of Schult and Soffel (1973). However, the value of these overall average poles in estimating absolute plate motion must await an understanding of the sources of the asymmetries in the paleomagnetic data.

When the dipole geomagnetic field dwindles away

1971 ◽  
Vol 2 (2) ◽  
pp. 29 ◽  
Author(s):  
R.A. Facer
Keyword(s):  
Geomagnetic Field ◽  
Dipole Field ◽  
Magnetic Studies ◽  
The Past ◽  
The Future ◽  
Intensity Study

It is now widely accepted that the geomagnetic field changes sign from time to time, generally irregularly, this "reversal" being accompanied by a decrease in intensity. Study of these changes in the past geomagnetic field has been limited to consideration of the dipole field. Unfortunately, the non-dipole geomagnetic field is more significant than has been considered previously - not only in palaeo-magnetism (Facer, 1970), but perhaps in the future in exploration magnetic studies also.

scholarly journals Earth’s magnetic field is probably not reversing

2018 ◽  
Vol 115 (20) ◽  
pp. 5111-5116 ◽  
Author(s):  
Maxwell Brown ◽  
Monika Korte ◽  
Richard Holme ◽  
Ingo Wardinski ◽  
Sydney Gunnarson
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Extreme Event ◽  
South Atlantic ◽  
Field Structure ◽  
Mono Lake ◽  
Dipole Field ◽  
South Atlantic Anomaly ◽  
Cosmogenic Nuclide ◽  
The Relationship

The geomagnetic field has been decaying at a rate of ∼5% per century from at least 1840, with indirect observations suggesting a decay since 1600 or even earlier. This has led to the assertion that the geomagnetic field may be undergoing a reversal or an excursion. We have derived a model of the geomagnetic field spanning 30–50 ka, constructed to study the behavior of the two most recent excursions: the Laschamp and Mono Lake, centered at 41 and 34 ka, respectively. Here, we show that neither excursion demonstrates field evolution similar to current changes in the geomagnetic field. At earlier times, centered at 49 and 46 ka, the field is comparable to today’s field, with an intensity structure similar to today’s South Atlantic Anomaly (SAA); however, neither of these SAA-like fields develop into an excursion or reversal. This suggests that the current weakened field will also recover without an extreme event such as an excursion or reversal. The SAA-like field structure at 46 ka appears to be coeval with published increases in geomagnetically modulated beryllium and chlorine nuclide production, despite the global dipole field not weakening significantly in our model during this time. This agreement suggests a greater complexity in the relationship between cosmogenic nuclide production and the geomagnetic field than is commonly assumed.

V. The remanent magnetization of unstable Keuper Marls

1957 ◽  
Vol 250 (974) ◽  
pp. 130-143 ◽  
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Laboratory Experiments ◽  
Natural Remanent Magnetization ◽  
Single Domain ◽  
Dipole Field ◽  
Main Field ◽  
Axial Dipole ◽  
Geocentric Axial Dipole ◽  
Three Components

Measurements of the directions and intensities of magnetization of Keuper Marls from Sidmouth are described. The natural remanent magnetization of these rocks is shown to be unstable in the geomagnetic field. Certain laboratory experiments are described which show the natural remanent magnetization to consist of three components, a primary component created on, or soon after, deposition, in the same direction as that of the natural remanent magnetization of Keuper Sandstones and Marls described by Clegg, Almond & Stubbs (1954); a secondary component in the direction of a geocentric axial dipole field in Britain acquired since the last reversal of the main field and a temporary component built up by the geomagnetic field between collection and measurement. The temporary and secondary components are believed to be isothermal remanent magnetizations and to be due to the red haematite cement. Application of Néel’s theory of the magnetization of small single-domain particles shows that haematite grains of less than 0·15 μ in diameter will be magnetically unstable. The temporary and secondary components of magnetization are explained in terms of Néel’s theory. A suggested test of stability is described.

Evidence for geomagnetic field excursions and secular variation from the Wrangell Volcanics of Alaska

1976 ◽  
Vol 13 (4) ◽  
pp. 547-554 ◽  
Author(s):  
D. K. Bingham ◽  
D. B. Stone
Keyword(s):  
Geomagnetic Field ◽  
Remanent Magnetization ◽  
Lava Flows ◽  
Dipole Field ◽  
Common Occurrence ◽  
Late Tertiary ◽  
Field Activity ◽  
Field Excursion ◽  
Geocentric Axial Dipole ◽  
Final Flow

Paleomagnetic studies have been made on 36 late Tertiary lava flows (3–4 m.y.) from the Wrangell Volcanics. Final flow mean remanent magnetization directions show excursions of the geomagnetic field away from a mean corresponding to a geocentric axial dipole field. They also point to the possibility that such excursions may have been a more common occurrence at the time of extrusion of these lavas than appears to have been the case in Quaternary times. These excursions may be due to increased non-dipole field activity. Calculation of the paleosecular variation including field excursion data leads to high values of PSV which do not agree with existing models. Exclusion of field excursion data gives a result that is consistent with current PSV models, but does not allow differentiation between them.

Pulses and decay of the dipolar field during the Holocene

2020 ◽  
Author(s):  
Alicia González-López ◽  
Saioa A. Campuzano ◽  
Alberto Molina-Cardín ◽  
Francisco Javier Pavón-Carrasco ◽  
Angelo De Santis ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Dipole Field ◽  
Long Wavelength ◽  
Axial Dipole ◽  
Maximum Value ◽  
Mode Decomposition ◽  
The Fourier Transform ◽  
The Magnetic Field

<p>Temporal changes in the main geomagnetic field, the so-called secular variation, can range from decades to millennia without showing any clear periodicity. A better knowledge of the secular variation behaviour is important to determine the mechanisms that maintain the magnetic field and can help to establish constraints in dynamo theories. Considering that the magnetic dipole contributes to around 90 % of the total main field, we have searched for periodicities in this component over the last 10,000 years using four global paleomagnetic field reconstructions (SHA.DIF.14k, CALS10k2, BIGMUDI4 and SHAWQ2k). We have applied three techniques commonly used in signal analysis: a) the Fourier transform to identify the characteristic frequencies of the dipole field; b) the Empirical Mode Decomposition to separate the secular variation of the dipole into short and long wavelength signals; and c) the wavelet analysis to know how the characteristic periods are distributed over the time studied. Results show that for short-wavelength terms we find a recurrent periodicity of 700 – 800 years, present throughout most of the last 10,000 years with small variations. Focusing on long-wavelength terms for SHA.DIF.14k and CALS10k2, we observed a drop in the dipole field, controlled by the axial dipole, starting around 7000 BC. We have fitted it as an exponential decay obtaining a relaxation time of 8,000 – 10,000 years, which well agrees with the theoretical diffusion time of the geomagnetic field. The dipole field starts to increase around 4,500 BC for nearly 4,000 years. If we consider that this increase is comparable to the charge of a capacitor, it would give a characteristic time of 15,000 years. However, the theoretical maximum value obtained for the axial dipole field is never reached and the charge stops at 40 % around the year 100 AD. At that time, the dipole impulse ended and the present large trend dipole decrease seems to start, with a relaxation time of 13,000 years.</p>

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