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Articles de revues sur le sujet « Geomagnetic field variations and reversals »

Auteur : Grafiati

Publié le 10 mars 2023

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1

Kocharov, G. E., A. V. Blinov, A. N. Konstantinov et V. A. Levchenko. « Temporal 10Be and 14C Variations : A Tool for Paleomagnetic Research ». Radiocarbon 31, n^o 2 (1989) : 163–68. http://dx.doi.org/10.1017/s0033822200044829.

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Temporal variations of cosmogenic radionuclide atmospheric concentrations can be caused by such global phenomena as solar activity and geomagnetic field changes as well as atmospheric circulation processes. These causes can be distinguished by the comparison of several isotope records corresponding to the same time period. We discuss a possibility for reconstructing the geomagnetic moment during the last 30,000 years from the comparison of 10Be and 14C concentrations in terrestrial archives. The results agree with conventional paleomagnetic data and promise to enrich our knowledge of geomagnetic field variations and reversals.

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2

Kočí, Alois, et A. Janáčková. « Variations of the geomagnetic field at the time of reversals ». Studia Geophysica et Geodaetica 29, n^o 3 (septembre 1985) : 280–89. http://dx.doi.org/10.1007/bf01638439.

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3

Dobretsov, N. L., D. V. Metelkin et A. N. Vasilevskiy. « Typical Characteristics of the Earth’s Magnetic and Gravity Fields Related to Global and Regional Tectonics ». Russian Geology and Geophysics 62, n^o 1 (1 janvier 2021) : 6–24. http://dx.doi.org/10.2113/rgg20204261.

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Abstract —We present a summary and analysis of current views on the magnetic and gravity fields of the Earth as a reflection of global and regional tectonic processes. The discussion concerns the probable interconnection between the distribution of the geomagnetic field characteristics, gravity anomalies and the manifestations of mantle plume magmatism as the most remarkable geologic indicator of deep geodynamics. We demonstrate that the distribution of the characteristics of the main geomagnetic field has a qualitative similarity to anomalies of the gravity field. Brief variations of the geomagnetic field are due to high-frequency oscillations in the ionosphere, do not affect the general state of the field, and are useless when considering issues of global tectonics. On the contrary, variations with long periodicities, first of all geomagnetic reversals, can be among the main indicators of the evolution of the geodynamo – the heat mechanism controlling the entire series of global tectonic processes. The frequency of reversals is determined by the intensity of mantle plumes that cause the cooling of the core, increase the convection rate in the asthenosphere, and respectively, the periodic changes in the tectonosphere. We assume the existence of three modes of behavior for this system. The first one corresponds to steady convection, in which reversals are extremely rare or do not happen at all. These episodes – superchrons – compose no more than 20% of the duration of the Phanerozoic. The second mode occurs significantly more often in the geologic history and is characterized by active convection with frequent reversals happening at least once every 5 Myr. Finally, the third mode, which is rare for the Phanerozoic but was probably more prevalent in the early Precambrian, corresponds to hyperactive turbulent convection, when the frequency of reversals reached 20 and possibly more during one million years. Although the demonstrated qualitative similarity in the position of extreme values of the main geomagnetic field, the centers of free air gravity anomalies, and manifestations of large igneous provinces does not yet have a credible explanation, we consider it to be fundamental and requiring special study and detailed elaboration.

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Maffei, Stefano, Philip W. Livermore, Jon E. Mound, Sam Greenwood et Christopher J. Davies. « Fast Directional Changes during Geomagnetic Transitions : Global Reversals or Local Fluctuations ? » Geosciences 11, n^o 8 (28 juillet 2021) : 318. http://dx.doi.org/10.3390/geosciences11080318.

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Paleomagnetic investigations from sediments in Central and Southern Italy found directional changes of the order of 10∘ per year during the last geomagnetic field reversal (which took place about 780,000 years ago). These values are orders of magnitudes larger than what is expected from the estimated millennial timescales for geomagnetic field reversals. It is yet unclear whether these extreme changes define the timescale of global dipolar change or whether they indicate a rapid, but spatially localised feature that is not indicative of global variations. Here, we address this issue by calculating the minimum amount of kinetic energy that flows at the top of the core required to instantaneously reproduce these two scenarios. We found that optimised flow structures compatible with the global-scale interpretation of directional change require about one order of magnitude more energy than those that reproduce local change. In particular, we found that the most recently reported directional variations from the Sulmona Basin, in Central Italy, can be reproduced by a core-surface flow with rms values comparable to, or significantly lower than, present-day estimates of about 8 to 22 km/y. Conversely, interpreting the observations as global changes requires rms flow values in excess of 77 km/y, with pointwise maximal velocities of 127 km/y, which we deem improbable. We therefore concluded that the extreme variations reported for the Sulmona Basin were likely caused by a local, transient feature during a longer transition.

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Merrill, R. T., et P. L. McFadden. « Secular variation and the origin of geomagnetic field reversals ». Journal of Geophysical Research 93, B10 (1988) : 11589. http://dx.doi.org/10.1029/jb093ib10p11589.

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Ryan, David A., et Graeme R. Sarson. « A coupled low order dynamo/turbulent shell model for geomagnetic field variations and reversals ». Physics of the Earth and Planetary Interiors 188, n^o 3-4 (octobre 2011) : 214–34. http://dx.doi.org/10.1016/j.pepi.2011.09.003.

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7

Ultré-Guérard, Pascale, et José Achache. « Core flow instabilities and geomagnetic storms during reversals : The Steens Mountain impulsive field variations revisited ». Earth and Planetary Science Letters 135, n^o 1-4 (octobre 1995) : 91–99. http://dx.doi.org/10.1016/0012-821x(95)00149-7.

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MOCHIZUKI, Nobutatsu, et Hideo TSUNAKAWA. « Geomagnetic Field Variations at the Beginning of the Polarity Reversal ». Journal of Geography (Chigaku Zasshi) 114, n^o 2 (2005) : 194–200. http://dx.doi.org/10.5026/jgeography.114.2_194.

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9

Pal, Poorna C. « The palaeogeomagnetic field strength, variations in reversal frequency, and geomagnetic dynamo models ». Geophysical & ; Astrophysical Fluid Dynamics 44, n^o 1-4 (décembre 1988) : 189–205. http://dx.doi.org/10.1080/03091928808208885.

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10

Abrahamsen, Niels, et Peter W. Readma. « Geomagnetic secular variation in Late Weichselian Allerød sediments from Nr. Lyngby (Denmark) ». Bulletin of the Geological Society of Denmark 44 (15 mars 1997) : 45–58. http://dx.doi.org/10.37570/bgsd-1998-44-03.

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Palaeomagnetic measurements on 400 specimens from lake sediments exposed in the cliff of the classic Late Glacial Allerød site at Nørre Lyngby in North Jutland, Denmark, are presented. Two profiles in the 7 m sequence of sand, silt and gyttja, spanning the time interval between c. 12 000 and c. 10 700 BP show about 5 cycles in the declination and about 2 cycles in inclination. Secular variation features as observed at this site are also recognizable at sites in southern Sweden and Soviet Karelia. Comparisons with Holocene records indicate that the short time-scale behaviour (i.e. < 103 y) of the geomagnetic field appears to have been similar since 14 000 BP, i.e. for a period considerably longer than the timescale of the variations themselves, thus suggesting that this type of behaviour is a permanent feature of the geomagnetic field. These secular variation features may be useful in local as well as more regional stratigraphical correlations for the Late Glacial and Holocene on a much more detailed timescale than is obtained from the magnetic reversal timescale used for older materials.

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11

Shcherbakova, V. V., A. J. Biggin, R. V. Veselovskiy, A. V. Shatsillo, L. M. A. Hawkins, V. P. Shcherbakov et G. V. Zhidkov. « Was the Devonian geomagnetic field dipolar or multipolar ? Palaeointensity studies of Devonian igneous rocks from the Minusa Basin (Siberia) and the Kola Peninsula dykes, Russia ». Geophysical Journal International 209, n^o 2 (28 février 2017) : 1265–86. http://dx.doi.org/10.1093/gji/ggx085.

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Abstract Defining variations in the behaviour of the geomagnetic field through geological time is critical to understanding the dynamics of Earth's core and its response to mantle convection and planetary evolution. Furthermore, the question of whether the axial dipole dominance of the recent palaeomagnetic field persists through the whole of Earth's history is fundamental to determining the reliability of palaeogeographic reconstructions and the efficacy of the magnetosphere in shielding Earth from solar wind radiation. Previous palaeomagnetic directional studies have suggested that the palaeofield had a complex configuration in the Devonian period (419–359 Ma). Here we present new high-quality palaeointensity determinations from rocks aged between 408 and 375 Ma from the Minusa Basin (southern Siberia), and the Kola Peninsula that enable the first reliable investigation of the strength of the field during this enigmatic period. Palaeointensity experiments were performed using the thermal Thellier, microwave Thellier and Wilson methods on 165 specimens from 25 sites. Six out of eight successful sites from the Minusa Basin and all four successful sites from the Kola Peninsula produced extremely low palaeointensities (<10 μT). These findings challenge the uniformitarian view of the palaeomagnetic field: field intensities of nearly an order of magnitude lower than Neogene values (except during relatively rare geomagnetic excursions and reversals) together with the widespread appearance of strange directions found in the Devonian suggest that the Earth's field during this time may have had a dominantly multipolar geometry. A persistent, low intensity multipolar magnetic field and associated diminished magnetosphere would increase the impact of solar particles on the Earth's magnetosphere, ionosphere and atmosphere with potential major implications for Earth's climate and biosphere.

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Silva, Regia Pereira, Jose Humberto Andrade Sobral, Daiki Koga et Jonas Rodrigues Souza. « Evidence of prompt penetration electric fields during HILDCAA events ». Annales Geophysicae 35, n^o 5 (27 octobre 2017) : 1165–76. http://dx.doi.org/10.5194/angeo-35-1165-2017.

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Abstract. High-intensity, long-duration continuous auroral electrojet (AE) activity (HILDCAA) events may occur during a long-lasting recovery phase of a geomagnetic storm. They are a special kind of geomagnetic activity, different from magnetic storms or substorms. Ionized particles are pumped into the auroral region by the action of Alfvén waves, increasing the auroral current system. The Dst index, however, does not present a significant downward swing as it occurs during geomagnetic storms. During the HILDCAA occurrence, the AE index presents an intense and continuous activity. In this paper, the response of Brazilian equatorial ionosphere is studied during three HILDCAA events that occurred in the year of 2006 (the descending phase of solar cycle 23) using the digisonde data located at São Luís, Brazil (2.33° S, 44.2° W; dip latitude 1.75° S). Geomagnetic indices and interplanetary parameters were used to calculate a cross-correlation coefficient between the Ey component of the interplanetary electric field and the F2 electron density peak height variations during two situations: the first of them for two sets daytime and nighttime ranges, and the second one for the time around the pre-reversal enhancement (PRE) peak. The results showed that the pumping action of particle precipitation into the auroral zone has moderately modified the equatorial F2 peak height. However, F2 peak height seems to be more sensitive to HILDCAA effects during PRE time, showing the highest variations and sinusoidal oscillations in the cross-correlation indices.

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13

Nowaczyk, Norbert R., Jiabo Liu et Helge W. Arz. « Records of the Laschamps geomagnetic polarity excursion from Black Sea sediments : magnetite versus greigite, discrete sample versus U-channel data ». Geophysical Journal International 224, n^o 2 (23 octobre 2020) : 1079–95. http://dx.doi.org/10.1093/gji/ggaa506.

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SUMMARY Magnetostratigraphic investigation of sediment cores from two different water depths in the SE Black Sea based on discrete samples, and parallel U-channels in one of the cores, yielded high-resolution records of geomagnetic field variations from the past about 68 ka. Age constrains are provided by three tephra layers of known age, accelerator mass spectrometry 14C dating, and by tuning element ratios obtained from X-ray fluorescence scanning to the oxygen isotope record from Greenland ice cores. Sedimentation rates vary from a minimum of ∼5 cm ka−1 in the Holocene to a maximum of ∼50 cm ka−1 in glacial marine isotope stage 4. Completely reversed inclinations and declinations as well as pronounced lows in relative palaeointensity around 41 ka provide evidence for the Laschamps geomagnetic polarity excursion. In one of the investigated cores also a fragmentary record of the Mono Lake excursion at 34.5 ka could be revealed. However, the palaeomagnetic records are more or less affected by greigite, a diagenetically formed magnetic iron sulphide. By definition of an exclusion criterion based on the ratio of saturation magnetization over volume susceptibility, greigite-bearing samples were removed from the palaeomagnetic data. Thus, only 25–55 per cent of the samples were left in the palaeomagnetic records obtained from sediments from the shallower coring site. The palaeomagnetic record from the deeper site, based on both discrete samples and U-channels, is much less affected by greigite. The comparison of palaeomagnetic data shows that the major features of the Laschamps polarity excursion were similarly recovered by both sampling techniques. However, several intervals had to be removed from the U-channel record due to the presence of greigite, carrying anomalous directions. By comparison to discrete sample data, also some directional artefacts in the U-channel record, caused by low-pass filtering of the broad magnetometer response functions, averaging across fast directional and large amplitude changes, can be observed. Therefore, high-resolution sampling with discrete samples should be the preferred technique when fast geomagnetic field variations, such as reversals and excursions, shall be studied from sedimentary records in the very detail.

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Zotov, Oleg, Anatol Guglielmi et Aleksandra Silina. « On possible relation of earthquakes with the sign change of the interplanetary magnetic field radial component ». Solar-Terrestrial Physics 7, n^o 1 (29 mars 2021) : 59–66. http://dx.doi.org/10.12737/stp-71202108.

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This work is devoted to an experimental study of the possible relationship between earthquakes and interplanetary magnetic field (IMF) variations. For the analysis, we use world and regional catalogs of earthquakes and a catalog containing data on the IMF sector structure for several decades. The main methodological technique consists in a comparative analysis of the occurrence rate of earthquakes on the days when Earth crosses the boundary between IMF sectors with the days when Earth is inside the sector. The sign of the IMF radial component is utilized as an indicator of the events on which the oscillation mode of Earth's magnetosphere depends. The sign reversal signals the probable crossing of the boundary between the IMF sectors by Earth, or, in other words, the crossing of the heliospheric current sheet by Earth. The hypothesis about the relationship between IMF variations and seismic activity is that IMF fluctuations, penetrating into the magnetosphere, excite ULF electromagnetic oscillations in the magnetosphere, which, in principle, can affect the physical processes in upcoming earthquake sources. We have found a weak, but statistically significant relationship between IMF variations and seismic activity. We also consider other IMF parameters that control ultra-low-frequency oscillations of the geomagnetic field.

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15

Prévot, Michel, Edward A. Mankinen, Robert S. Coe et C. Sherman Grommé. « The Steens Mountain (Oregon) geomagnetic polarity transition : 2. Field intensity variations and discussion of reversal models ». Journal of Geophysical Research 90, B12 (1985) : 10417. http://dx.doi.org/10.1029/jb090ib12p10417.

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16

Zotov, Oleg, Anatol Guglielmi et Aleksandra Silina. « On possible relation of earthquakes with the sign change of the interplanetary magnetic field radial component ». Solnechno-Zemnaya Fizika 7, n^o 1 (29 mars 2021) : 74–83. http://dx.doi.org/10.12737/szf-71202108.

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This work is devoted to an experimental study of the possible relationship between earthquakes and interplanetary magnetic field (IMF) variations. For the analysis, we use world and regional catalogs of earthquakes and a catalog containing data on the IMF sector structure for several decades. The main methodological technique consists in a comparative analysis of the occurrence rate of earthquakes on the days when Earth crosses the boundary between IMF sectors with the days when Earth is inside the sector. The sign of the IMF radial component is utilized as an indicator of the events on which the oscillation mode of Earth's magnetosphere depends. The sign reversal signals the probable crossing of the boundary between the IMF sectors by Earth, or, in other words, the crossing of the heliospheric current sheet by Earth. The hypothesis about the relationship between IMF variations and seismic activity is that IMF fluctuations, penetrating into the magnetosphere, excite ULF electromagnetic oscillations in the magnetosphere, which, in principle, can affect the physical processes in upcoming earthquake sources. We have found a weak, but statistically significant relationship between IMF variations and seismic activity. We also consider other IMF parameters that control ultra-low-frequency oscillations of the geomagnetic field.

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17

Nowaczyk, N. R., E. M. Haltia, D. Ulbricht, V. Wennrich, M. A. Sauerbrey, P. Rosén, H. Vogel et al. « Chronology of Lake El'gygytgyn sediments – a combined magnetostratigraphic, palaeoclimatic and orbital tuning study based on multi-parameter analyses ». Climate of the Past 9, n^o 6 (1 novembre 2013) : 2413–32. http://dx.doi.org/10.5194/cp-9-2413-2013.

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Abstract. A 318-metre-long sedimentary profile drilled by the International Continental Scientific Drilling Program (ICDP) at Site 5011-1 in Lake El'gygytgyn, Far East Russian Arctic, has been analysed for its sedimentologic response to global climate modes by chronostratigraphic methods. The 12 km wide lake is sited off-centre in an 18 km large crater that was created by the impact of a meteorite 3.58 Ma ago. Since then sediments have been continuously deposited. For establishing their chronology, major reversals of the earth's magnetic field provided initial tie points for the age model, confirming that the impact occurred in the earliest geomagnetic Gauss chron. Various stratigraphic parameters, reflecting redox conditions at the lake floor and climatic conditions in the catchment were tuned synchronously to Northern Hemisphere insolation variations and the marine oxygen isotope stack, respectively. Thus, a robust age model comprising more than 600 tie points could be defined. It could be shown that deposition of sediments in Lake El'gygytgyn occurred in concert with global climatic cycles. The upper ~160 m of sediments represent the past 3.3 Ma, equivalent to sedimentation rates of 4 to 5 cm ka−1, whereas the lower 160 m represent just the first 0.3 Ma after the impact, equivalent to sedimentation rates in the order of 45 cm ka−1. This study also provides orbitally tuned ages for a total of 8 tephras deposited in Lake El'gygytgyn.

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de Paor, A. « A theory of the Earth's magnetic field and of sunspots, based on a self-excited dynamo incorporating the Hall effect ». Nonlinear Processes in Geophysics 8, n^o 4/5 (31 octobre 2001) : 265–79. http://dx.doi.org/10.5194/npg-8-265-2001.

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Abstract. A new viewpoint on the generation and maintenance of the Earth's magnetic field is put forward, which integrates self-exciting dynamo theory with the possibility of energy coupling along orthogonal axes provided by the Hall effect. A nonlinear third-order system is derived, with a fourth equation serving as an observer of unspecified geophysical processes which could result in field reversal. Lyapunov analysis proves that chaos is not intrinsic to this system. Relative constancy of one of the variables produces pseudo equilibrium in a second order subsystem and allows for self-excitation of the geomagnetic field. Electromagnetic analysis yields expressions for key parameters. Models for secular variations recorded at London, Palermo and at the Cape of Good Hope over the past four hundred years are offered. Offset of the Earth's magnetic axis from the geographic axis is central to time-varying declination, but its causes have not yet been established. Applicability of the model to the explanation of sunspot activity is outlined. A corroborating experiment published by Peter Barlow in 1831 is appended.

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Chapanov, Yavor, et Daniel Gambis. « Solar-terrestrial energy transfer during sunspot cycles and mechanism of Earth rotation excitation ». Proceedings of the International Astronomical Union 5, S264 (août 2009) : 404–6. http://dx.doi.org/10.1017/s1743921309992997.

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AbstractThe solar-terrestrial energy transfer, due to the total solar irradiance (TSI), solar wind and interplanetary magnetic field, has 11-year modulation during the sunspot cycles. Other oscillations of solar-terrestrial energy transfer are with periods of 22 and 45 year due to the magnetic reversal and equatorial solar asymmetry, which cause corresponding oscillations of all Earth systems, including climate and weather, atmosphere and ocean circulations, geomagnetic field and core processes. A part of this energy variation is transformed to oscillations of the Earth rotation. A model of indirect mechanism of Earth rotation excitation during sunspot cycles is proposed, which is based on global water circulation and periodical mass transfer between oceans and polar ice caps. The oscillations of the mean sea level (MSL) with periods 11, 22 and 45 years are determined by sea level data for the last two centuries from 13 maregraph stations. The necessary energy of water evaporation, corresponding to the observed MSL variations is provided by TSI oscillations with amplitudes between 0.2-0.5W/m2, determined by means of reconstructed time series of the TSI since 1610. The determined mean Universal Time (UT1) amplitudes, corresponding to the 22-year and 45-year cycles of the solar activity are 185ms and 310ms.

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Sahai, Y., P. R. Fagundes, R. de Jesus, A. J. de Abreu, G. Crowley, T. Kikuchi, C. S. Huang et al. « Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005 ». Annales Geophysicae 29, n^o 5 (27 mai 2011) : 919–29. http://dx.doi.org/10.5194/angeo-29-919-2011.

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Abstract. In the present investigation, we have studied the response of the ionospheric F-region in the Latin American sector during the intense geomagnetic storm of 21–22 January 2005. This geomagnetic storm has been considered "anomalous" (minimum Dst reached −105 nT at 07:00 UT on 22 January) because the main storm phase occurred during the northward excursion of the Bz component of interplanetary magnetic fields (IMFs). The monthly mean F10.7 solar flux for the month of January 2005 was 99.0 sfu. The F-region parameters observed by ionosondes at Ramey (RAM; 18.5° N, 67.1° W), Puerto Rico, Jicamarca (JIC; 12.0° S, 76.8° W), Peru, Manaus (MAN; 2.9° S, 60.0° W), and São José dos Campos (SJC; 23.2° S, 45.9° W), Brazil, during 21–22 January (geomagnetically disturbed) and 25 January (geomagnetically quiet) have been analyzed. Both JIC and MAN, the equatorial stations, show unusually rapid uplifting of the F-region peak heights (hpF2/hmF2) and a decrease in the NmF2 coincident with the time of storm sudden commencement (SSC). The observed variations in the F-region ionospheric parameters are compared with the TIMEGCM model run for 21–22 January and the model results show both similarities and differences from the observed results. Average GPS-TEC (21, 22 and 25 January) and phase fluctuations (21, 22, 25, 26 January) observed at Belem (BELE; 1.5° S, 48.5° W), Brasilia (BRAZ; 15.9° S, 47.9° W), Presidente Prudente (UEPP; 22.3° S, 51.4° W), and Porto Alegre (POAL; 30.1° S, 51.1° W), Brazil, are also presented. These GPS stations belong to the RBMC/IBGE network of Brazil. A few hours after the onset of the storm, large enhancements in the VTEC and NmF2 between about 20:00 and 24:00 UT on 21 January were observed at all the stations. However, the increase in VTEC was greatest at the near equatorial station (BELE) and enhancements in VTEC decreased with latitude. It should be pointed out that no phase fluctuations or spread-F were observed in the Latin American sector during the post-sunset pre-reversal time in the geomagnetic disturbance (21 January). The disturbance dynamo electric field possibly resulted in downward drift of the F-region plasma and inhibited the formation of spread-F.

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McFadden, P. L., et R. T. Merrill. « Inhibition and geomagnetic field reversals ». Journal of Geophysical Research : Solid Earth 98, B4 (10 avril 1993) : 6189–99. http://dx.doi.org/10.1029/92jb02574.

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Valet, Jean-Pierre, Alexandre Fournier, Vincent Courtillot et Emilio Herrero-Bervera. « Dynamical similarity of geomagnetic field reversals ». Nature 490, n^o 7418 (octobre 2012) : 89–93. http://dx.doi.org/10.1038/nature11491.

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Bogue, Scott W., et Hilary A. Paul. « Distinctive field behavior following geomagnetic reversals ». Geophysical Research Letters 20, n^o 21 (5 novembre 1993) : 2399–402. http://dx.doi.org/10.1029/93gl02473.

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Gurarii, G. Z., M. V. Aleksyutin et N. Ataev. « Wavelet analysis of paleomagnetic data : 1. Characteristic average times (5–10 kyr) of variations in the geomagnetic field during and immediately before and after the Early Jaramillo reversal (Western Turkmenistan) ». Izvestiya, Physics of the Solid Earth 43, n^o 10 (octobre 2007) : 819–29. http://dx.doi.org/10.1134/s1069351307100047.

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Gurarii, G. Z. « Geomagnetic field reversals : Main results and basic problems ». Russian Journal of Earth Sciences 7, n^o 3 (22 juin 2005) : 1–13. http://dx.doi.org/10.2205/2005es000175.

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Reshetnyak, M. Yu. « Geostrophic balance and reversals of the geomagnetic field ». Russian Journal of Earth Sciences 13, n^o 1 (17 mars 2013) : 1–6. http://dx.doi.org/10.2205/2013es000526.

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Wicht, Johannes, et Domenico G. Meduri. « A gaussian model for simulated geomagnetic field reversals ». Physics of the Earth and Planetary Interiors 259 (octobre 2016) : 45–60. http://dx.doi.org/10.1016/j.pepi.2016.07.007.

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Bogue, S. W., et R. T. Merrill. « The Character of the Field During Geomagnetic Reversals ». Annual Review of Earth and Planetary Sciences 20, n^o 1 (mai 1992) : 181–219. http://dx.doi.org/10.1146/annurev.ea.20.050192.001145.

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McFadden, P. L., et R. T. Merrill. « Sawtooth paleointensity and reversals of the geomagnetic field ». Physics of the Earth and Planetary Interiors 103, n^o 3-4 (novembre 1997) : 247–52. http://dx.doi.org/10.1016/s0031-9201(97)00036-8.

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Coe, Robert S., et Michel Prévot. « Evidence suggesting extremely rapid field variation during a geomagnetic reversal ». Earth and Planetary Science Letters 92, n^o 3-4 (avril 1989) : 292–98. http://dx.doi.org/10.1016/0012-821x(89)90053-8.

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Gurarii, G. Z. « Wavelet analysis of paleomagnetic data : 5. Early Jaramillo reversal and main characteristic times in the interval from 3 to 70 ka in the variations of the elements of geomagnetic field (Western Turkmenia) ». Izvestiya, Physics of the Solid Earth 49, n^o 1 (janvier 2013) : 130–43. http://dx.doi.org/10.1134/s1069351312100011.

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Séran, E., H. U. Frey, M. Fillingim, J. J. Berthelier, R. Pottelette et G. Parks. « Demeter high resolution observations of the ionospheric thermal plasma response to magnetospheric energy input during the magnetic storm of November 2004 ». Annales Geophysicae 25, n^o 12 (2 janvier 2007) : 2503–11. http://dx.doi.org/10.5194/angeo-25-2503-2007.

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Abstract. High resolution Demeter plasma and wave observations were available during one of the geomagnetic storms of November 2004 when the ionospheric footprint of the plasmasphere was pushed below 64 degrees in the midnight sector. We report here onboard observations of thermal/suprathermal plasma and HF electric field variations with a temporal resolution of 0.4 s, which corresponds to a spatial resolution of 3 km. Local perturbations of the plasma parameters at the altitude of 730 km are analysed with respect to the variation of the field-aligned currents, electron and proton precipitation and large-scale electric fields, measured in-situ by Demeter and by remote optical methods from the IMAGE/Polar satellites. Flow monitoring in the 21:00 and 24:00 MLT sectors during storm conditions reveals two distinct regions of O+ outflow, i.e. the region of the field-aligned currents, which often comprises few layers of opposite currents, and the region of velocity reversal toward dusk at sub-auroral latitudes. Average upward O+ velocities are identical in both local time sectors and vary between 200 and 450 m s−1, with an exception of a few cases of higher speed (~1000 m s−1) outflow, observed in the midnight sector. Each individual outflow event does not indicate any heating process of the thermal O+ population. On the contrary, the temperature of the O+, outflowing from auroral latitudes, is found to be even colder than that of the ambient ion plasma. The only ion population which is observed to be involved in the heating is the O+ with energies a few times higher than the thermal energy. Such a population was detected at sub-auroral latitudes in the region of duskward flow reversal. Its temperature raises up to a few eV inside the layer of sheared velocity. A deep decrease in the H+ density at heights and latitudes, where, according to the IRI model, these ions are expected to comprise ~50% of the positive charge, indicates that the thermospheric balance between atomic oxygen and hydrogen was re-established in favour of oxygen. As a consequence, the charge exchange between oxygen and hydrogen does not effectively limit the O+ production in the regions of the electron precipitation. According to Demeter observations, the O+ concentration is doubled inside the layers with upward currents (downward electrons). Such a density excess creates the pressure gradient which drives the plasma away from the overdense regions, i.e. first, from the layers of precipitating electrons and then upward along the layers of downward current. In addition, the downward currents are identified to be the source regions of hiss emissions, i.e. electron acoustic mode excited via the Landau resonance in the multi-component electron plasma. Such instabilities, which are often observed in the auroral region at 2–5 Earth radii, but rarely at ionospheric altitudes, are believed to be generated by an electron beam which moves through the background plasma with a velocity higher than its thermal velocity.

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Engbers, Yael A., Andrew J. Biggin et Richard K. Bono. « Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic ». Proceedings of the National Academy of Sciences 117, n^o 31 (20 juillet 2020) : 18258–63. http://dx.doi.org/10.1073/pnas.2001217117.

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Earth’s magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth’s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core−mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core−mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.

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Gurarii, G. Z., M. V. Aleksyutin et N. M. Ataev. « Wavelet analysis of paleomagnetic data : 4. Characteristic short times (0.4–4.5 ky) of variations in the elements of the geomagnetic field during the early Jaramillo reversal and in the stationary field during the Matuyama and Jaramillo chrons (Western Turkmenia) ». Izvestiya, Physics of the Solid Earth 48, n^o 4 (avril 2012) : 306–19. http://dx.doi.org/10.1134/s1069351312040027.

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Barbosa, Cleiton S., Douglas S. R. Ferreira, Marco A. do Espírito Santo et Andrés R. R. Papa. « Statistical analysis of geomagnetic field reversals and their consequences ». Physica A : Statistical Mechanics and its Applications 392, n^o 24 (décembre 2013) : 6554–60. http://dx.doi.org/10.1016/j.physa.2013.08.025.

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Fagre, Mariano, Bruno S. Zossi, Erdal Yiğit, Hagay Amit et Ana G. Elias. « High frequency sky wave propagation during geomagnetic field reversals ». Studia Geophysica et Geodaetica 64, n^o 1 (20 décembre 2019) : 130–42. http://dx.doi.org/10.1007/s11200-019-1154-2.

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NARTEAU, C., J. LEMOUEL et J. VALET. « The oscillatory nature of the geomagnetic field during reversals ». Earth and Planetary Science Letters 262, n^o 1-2 (15 octobre 2007) : 66–76. http://dx.doi.org/10.1016/j.epsl.2007.07.007.

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Chou, Yu-Min, Xiuyang Jiang, Qingsong Liu, Hsun-Ming Hu, Chung-Che Wu, Jianxing Liu, Zhaoxia Jiang et al. « Multidecadally resolved polarity oscillations during a geomagnetic excursion ». Proceedings of the National Academy of Sciences 115, n^o 36 (20 août 2018) : 8913–18. http://dx.doi.org/10.1073/pnas.1720404115.

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Polarity reversals of the geomagnetic field have occurred through billions of years of Earth history and were first revealed in the early 20th century. Almost a century later, details of transitional field behavior during geomagnetic reversals and excursions remain poorly known. Here, we present a multidecadally resolved geomagnetic excursion record from a radioisotopically dated Chinese stalagmite at 107–91 thousand years before present with age precision of several decades. The duration of geomagnetic directional oscillations ranged from several centuries at 106–103 thousand years before present to millennia at 98–92 thousand years before present, with one abrupt reversal transition occurring in one to two centuries when the field was weakest. These features indicate prolonged geodynamo instability. Repeated asymmetrical interhemispheric polarity drifts associated with weak dipole fields likely originated in Earth’s deep interior. If such rapid polarity changes occurred in future, they could severely affect satellites and human society.

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Feschenko, L. K., et G. M. Vodinchar. « Reversals in the large-scale αΩ-dynamo with memory ». Nonlinear Processes in Geophysics 22, n^o 4 (7 juillet 2015) : 361–69. http://dx.doi.org/10.5194/npg-22-361-2015.

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Abstract. Inversion of the magnetic field in a model of large-scale αΩ-dynamo with α-effect with stochastic memory is under investigation. The model allows us to reproduce the main features of the geomagnetic field reversals. It was established that the polarity intervals in the model are distributed according to the power law. Model magnetic polarity timescale is fractal. Its dimension is consistent with the dimension of the real geomagnetic polarity timescale.

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SORRISO-VALVO, LUCA, VINCENZO CARBONE, MICHAEL BOURGOIN, PHILIPPE ODIER, NICOLAS PLIHON et ROMAIN VOLK. « STATISTICAL ANALYSIS OF MAGNETIC FIELD REVERSALS IN LABORATORY DYNAMO AND IN PALEOMAGNETIC MEASUREMENTS ». International Journal of Modern Physics B 23, n^o 28n29 (20 novembre 2009) : 5483–91. http://dx.doi.org/10.1142/s0217979209063791.

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Statistical properties of the temporal distribution of polarity reversals of the geomagnetic field are commonly assumed to be a realization of a renewal Poisson process with a variable rate. However, it has been recently shown that the polarity reversals strongly depart from a local Poisson statistics, because of temporal clustering. Such clustering arises from the presence of long-range correlations in the underlying dynamo process. Recently achieved laboratory dynamo also shows reversals. It is shown here that laboratory and paleomagnetic data are both characterized by the presence of long-range correlations.

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Xi, Xiao Wen, Shang Kun Ren et Li Hua Yuan. « Finite Element Analysis of Magnetization Reversal Effect Based on Ferromagnetic Specimens ». Applied Mechanics and Materials 620 (août 2014) : 127–32. http://dx.doi.org/10.4028/www.scientific.net/amm.620.127.

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Using large finite element analysis (FEA) software ANSYS, the stress-magnetization effect on 20# steel specimens with different shape notches is simulated under the geomagnetic field and tensile load. With the stimulation, the magnetic flux leakage fields at certain positions of the surface specimen were measured. Through analysis the relationship between the magnetic flux leakage fields of certain points with tensile stress, the results showed that the magnetic field value at certain positions of specimen surface first decreases and then increases along with the increase of stress, which is called magnetization reversal phenomenon; Different gaps and different positions of the specimen show different magnetization reversal rules; By measuring the maximal variation of the magnetic field value △Hmax at certain positions of the surface specimen and by analyzing its change law, we can roughly estimate specimen stress size and distribution regularity of stress. Moreover, this article also discusses the effect of lifts-off of the probe on the law of stress magnetization.

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Sokoloff, D. D., G. S. Sobko, V. I. Trukhin et V. N. Zadkov. « A model for grand minima and geomagnetic reversals ». Proceedings of the International Astronomical Union 7, S286 (octobre 2011) : 360–66. http://dx.doi.org/10.1017/s1743921312005091.

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AbstractWe suggest a simple dynamical system which mimics a nonlinear dynamo which is able to provide (in specific domains of its parametric space) the temporal evolution of solar magnetic activity cycles as well as evolution of geomagnetic field including its polarity reversals. A qualitative explanation for the physical nature of both phenomena is presented and discussed.

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Hoffman, K. A. « Findings suggest possible link between geomagnetic reversals and field intensity ». Eos, Transactions American Geophysical Union 76, n^o 29 (1995) : 289. http://dx.doi.org/10.1029/95eo00172.

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Sorriso-Valvo, Luca, Frank Stefani, Vincenzo Carbone, Giuseppina Nigro, Fabio Lepreti, Antonio Vecchio et Pierluigi Veltri. « A statistical analysis of polarity reversals of the geomagnetic field ». Physics of the Earth and Planetary Interiors 164, n^o 3-4 (octobre 2007) : 197–207. http://dx.doi.org/10.1016/j.pepi.2007.07.001.

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Molina-Cardín, Alberto, Luis Dinis et María Luisa Osete. « Simple stochastic model for geomagnetic excursions and reversals reproduces the temporal asymmetry of the axial dipole moment ». Proceedings of the National Academy of Sciences 118, n^o 10 (1 mars 2021) : e2017696118. http://dx.doi.org/10.1073/pnas.2017696118.

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We present a simple model for the axial dipole moment (ADM) of the geomagnetic field based on a stochastic differential equation for two coupled particles in a biquadratic potential, subjected to Gaussian random perturbations. This model generates aperiodic reversals and excursions separated by stable polarity periods. The model reproduces the temporal asymmetry of geomagnetic reversals, with slower decaying rates before the reversal and faster growing rates after it. This temporal asymmetry is possible because our model is out of equilibrium. The existence of a thermal imbalance between the two particles sets a preferential sense for the energy flux and renders the process irreversible.

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Korte, Monika, et Raimund Muscheler. « Centennial to millennial geomagnetic field variations ». Journal of Space Weather and Space Climate 2 (2012) : A08. http://dx.doi.org/10.1051/swsc/2012006.

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Feschenko, L. K., et G. M. Vodinchar. « Reversal in the nonlocal large-scale αΩ-dynamo ». Nonlinear Processes in Geophysics Discussions 1, n^o 2 (18 novembre 2014) : 1715–34. http://dx.doi.org/10.5194/npgd-1-1715-2014.

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Abstract. Inversion of the magnetic field in a large-scale model of αΩ-dynamo with nonlocal α-effect is under the investigation. The model allows us to reproduce the main features of the geomagnetic field reversals. It was established that the polarity intervals in the model are distributed according to the power law. Model magnetic polarity time scale is fractal. Its dimension is consistent with the dimension of the real geomagnetic polarity time scale.

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Henken-Mellies, W. U., J. Beer, F. Heller, K. J. Hsu¨, C. Shen et W. Wo¨lfli. « Be-10 variations in a south atlantic DSDP-core : Interrelation with geomagnetic reversals and climatic variations ». Chemical Geology 70, n^o 1-2 (août 1988) : 119. http://dx.doi.org/10.1016/0009-2541(88)90536-0.

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Valet, Jean-pierre, et Laure Meynadier. « Geomagnetic field intensity and reversals during the past four million years ». Nature 366, n^o 6452 (novembre 1993) : 234–38. http://dx.doi.org/10.1038/366234a0.

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Pierre Valet, Jean, Piotr Tucholka, Vincent Courtillot et Laure Meynadier. « Palaeomagnetic constraints on the geometry of the geomagnetic field during reversals ». Nature 356, n^o 6368 (avril 1992) : 400–407. http://dx.doi.org/10.1038/356400a0.

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