Magnetic North Research Articles

Paleomagnetic Secular Variations in North Greenland Around 81°N Over the Last 6,000 Years

AbstractWe investigate full vector paleomagnetic changes recorded in high‐resolution sediments of Petermann Fjord, North Greenland, deposited over the last 6 kyr, in the context of the recent rapid changes in the geomagnetic field. A Paleomagnetic Secular Variation (PSV) stack (inclination, declination, and relative paleointensity) was reconstructed using four marine sediment cores with an independent age model constrained by seven radiocarbon ages. Magnetic investigations demonstrate that the paleomagnetic signal is carried by low coercivity ferrimagnetic minerals and is well reproduced in all cores, attesting to the quality and reliability of the paleomagnetic recording of these sediments. This signal is broadly consistent in directional changes with distant records in North America and the northern North Atlantic at centennial and millennial timescales, and has millennial scale intensity variations that are consistent with model predictions. The offset between a magnetization age determined through comparison with a northern North Atlantic PSV reference curve, GREENICE, and the radiocarbon age model indicates either a reasonable lock‐in depth of magnetization (∼11 cm from the coretop) or centennial‐scale reservoir age variation through time in the fjord. Reconstructed virtual geomagnetic pole (VGP) migration for the last 6 kyr shows that the recent migration of the magnetic North Pole is consistent with secular paleomagnetic variations on geologic timescales. Our results suggest that magnetic field intensity variations (temporal and spatial) are linked to magnetic flux lobe dynamics and influence the VGP migration.

Оценки положения Северного магнитного полюса в 2021 году

Based on measurements of magnetic declinations with standard shipboard instruments in three marine expeditions in the Russian Arctic, estimates of the Earth`s North Magnetic Pole position in 2021 were obtained. It is located in the Russian sector of the Arctic. Experiments on determining the North Magnetic Pole in 2021 were carried out on board the research vessels “Professor Molchanov” and the scientific expedition one “Mikhail Somov” supported by the hydrographic ship of “Horizon”. The calculations used a comparison of measurements along the quasi-closed route with magnetic declination data using the International Geomagnetic Analytical Field IGRF13 (International Geomagnetic Reference Field) model with the choice of the minimum discrepancy, a simple inverse matching problem for smooth functions was solved. The results obtained confirm the possibility of regular operational assessment of the Earth`s magnetic poles position. The technology of assessing the magnetic deviation of ships is considered

Integrative mapping of radioactive and alteration zones in Um Had plutons, Egypt: Using Landsat 9, ASTER imagery, and airborne geophysical data

The study aims to assess the effectiveness of using ASTER, Landsat 9, and airborne geophysical data to generate maps depicting hydrothermally altered regions and their correlation with radioactive-mineralized zones in Egypt's Um Had area. Various image processing methods were applied, including color composite images, band ratios, selective principal component analyses, and lineament extraction with enhancement procedures. The ASTER ratios identified the three types of hydrothermal alterations; phyllic, argillic, and propylitic, with other significant alteration zones related to mineralization. Airborne gamma-ray spectrometry contour maps displayed marked varied levels of total count (T.C), eU, eTh, and K, ranging from 1.2 to 21.2 Ur, 0.5–12.34 ppm, 1.45–28 ppm, and 0.13–3.65 %, respectively. The highest anomalies of these radioelements concentration have coincided with the alkali feldspar granite and along their intrusive contact zone with the Hammamat Group sedimentary rocks. Higher anomalies are well recorded in the center and eastern regions of Um Had's, according to the radioelements composite image. The lowest concentrations of these radioelements are associated with gneiss, ophiolitic mélange, metavolcanic, Hammamat Group sedimentary rocks, Taref Formation, and Wadi sediments. To mitigate local magnetic effects, the total aeromagnetic data was reduced to the north magnetic pole (RTP). Power spectrum analysis of the RTP data identified distinct magnetic wavelengths for regional-residual components. In order to identify near-surface magnetic lineaments, such as contacts, shear zones, faults, and dykes, advanced algorithms were applied to the RTP data. The lineaments derived from ASTER and airborne magnetic data revealed dominant fault systems characterized by E–W, NE, NNW, NW and N–S trends, governing the structural framework of the study area. Depth levels of geological contacts and faults that represented pathways for altered and mineralized zones reached more than 1200 m (Euler deconvolution). These findings highlight the consistent results obtained when combining ASTER data with airborne survey data, allowing for the identification of hydrothermally altered zones and primary conductive zones.

Using Magnetic Fields to Enhance the Seed Germination, Growth, and Yield of Plants.

Geomagnetic field (GMF) protects living organisms on the Earth from the radiation coming from space along with other environmental factors during evolution, and it has affected the growth and development of plants. Many researchers have always been interested in investigating these effects in different aspects. In this chapter, we focus on the methods of using different types of magnetic fields (MFs) to investigate the dimensions of their biological effects on plants. The aim is to increase seed germination, growth characters, and yield of plants using the following methods: (1) Using MFs lower than GMF to study effects of GMF on the growth and yield of plants. (2) Using reversed magnetic fields (RMFs) lower than GMF to study its effects on the growth and development of plants during evolution. (3) Using static magnetic fields (SMFs) higher than GMF and reversed SMFs to study effects of the south (S) and north (N) magnetic pole on plants. (4) Using electromagnetic fields (EMFs) to increase and accelerate seed germination, growth, and yield of plants, and establish the status of plants against other environmental stresses. (5) Using magnetized water (MW) to improve plant seed germination, growth, and yield. (6) Using high gradient magnetic field (HGMF) to study magneto-tropism in plants. In this chapter, we recommend application of various types of MFs to study their biological effects on plants to improve crop production.

Study of the origin and correction of compass measurement errors in Doppler current meters

Surface and subsurface currents are two of the Essential Climate Variables (ECVs) defined by the Global Climate Observing System (GCOS). In situ current measurements can be made by Eulerian methods with instruments on moorings fixed in space. These methods require the determination of two metrological quantities: the speed and the direction of the motion. Their measurement and calibration require the determination of reference velocities and the measure of the angular movement of seawater in relation to the measuring device, as well as of the measuring device in relation to a reference direction given by the magnetic North. This reference direction is determined by electronic compasses integrated into current meters and current profilers. Compasses are sensitive to their magnetic environment, and, therefore, to the objects and instruments that surround them. This publication describes experiments conducted with current meters and current profilers to measure the influence of different devices on the accuracy of their compass measurements. It gives some explanations about the origin of measurement errors and proposes solutions to correct or attenuate the defaults in direction measurements and the measured deviations. Correction formulas are given that can be applied to measured data. They allow the reduction of errors of several tens of degrees for data to be within the instrument’s specifications.

A novel approach to seabird posture estimation: finding roll and yaw angles of dynamic soaring albatrosses using tri-axial magnetometers

With advances in bio-logging technology, the posture of animals is now commonly described by inertial measurement units, which include tri-axial accelerometers to estimate pitch and roll angles. Many large seabirds use dynamic soaring flight to travel long distances, but this low-cost flight mode results in high centripetal acceleration, which obscures posture derived from accelerometers. Tri-axial magnetometers are not influenced by acceleration and might provide a way to estimate the posture of animals that experience high centripetal acceleration. We propose a new method to estimate the posture of dynamic soaring seabirds using tri-axial magnetometer data, with the assumption that they do not have large pitch angles during routine flight. This method was field-tested by deploying a combination of bio-logging devices on three albatross species breeding on Marion Island, using bird-borne video loggers to validate the roll angles. Validated data showed that the method worked well in most instances, but accuracy decreased when the heading was close to magnetic north or south. Accurate, fine-scale posture estimates may provide insight into dynamic soaring flight and allow estimates of fine-scale tracks using dead-reckoning, not only for seabirds, but potentially for other species where centripetal acceleration limits the use of accelerometers to estimate posture.

Evaluation of Groundwater Potentiality and Subsurface Structural Setting by Using Geophysical Data in Wadi Hubuna, Southwest Najran, Saudi Arabia

A geophysical study was conducted to explore the shallow groundwater aquifer and to identify the subsurface structure on the basis of resistivity and geomagnetic surveys. The study area is situated in the southwestern portion of Saudi Arabia, southwest of the Najran region. The total intensity magnetic map is reduced to the northern magnetic pole. The estimated mean depths of the regional and residual magnetic sources are 3 km and 1.4 km respectively. Eighty vertical electrical soundings were measured using the Schlumberger configuration with AB/2 spacing of up to 700 m. Four geoelectrical layers were identified, and could be described from ground surface to deeper layers as the following: The first layer encompasses wadi deposits with true resistivity values ranging from 452 Ω.m to 1353 Ω.m and thicknesses of 2-4 m. The second layer is comprised of dry fine to medium grain-sized deposits with true resistivity values ranging from 104 Ω.m to 451 Ω.m, and thickness varying between 2 and 16 m. The third layer consists of water-bearing friable deposits beside the topmost part of the underlying weathered (fractured) basement. The true resistivity of this layer ranges from 22 Ω.m to 188 Ω.m, whereas the thickness of this layer is highly variable and ranges from 5 to 35 m. Generally, the resistivity values and the thickness of these three layers exhibit an increasing trend toward the main wadi stream. A fourth layer was also detected and is represented by a thin clay layer directly overlying the hard rocks of the basement complex. The dominant tectonic trends controlling the shallower parts are N-S and NNW-SSE. Meanwhile, the structural trend controlling the deeper parts is NE-SW, E-W, and. NNE-SSW. The ideal areas for drilling wells, according to the interpreted cross-sections, are along the main stream of Wadi hubuna and other small wadis, as well as the lower portions of the wadi in the extreme east direction.

Study on the Transition to True North in Air Navigation

The paper is an introductory study on the possible transition from Magnetic North reference to True North reference in air navigation, as envisaged by the International Association of Institutes of Navigation’s AHRTAG Group. The use of the Magnetic Field of the Earth as a direction reference in aviation is explained briefly. Magnetic North is an unstable and irregular directional reference that aviation manages well, but with significant costs. The unpredictability and uncertainties of the Magnetic Field of the Earth might be critical in the future, especially in the case of reversal of the magnetic poles, or incipient reversal. The paper puts forward the case for calculating the probability of such a catastrophic event, with a view to engaging further expert research in the geomagnetic phenomena. The purpose of such a probability estimate would be for the aviation decision makers to determine whether contingency planning might be required or not. Furthermore, the paper analyses the adoption of True North in maritime navigation as a possible model.

SEPARATION OF MAGNETIC ANOMALIES USING FRACTAL METHOD IN THE ESFORDI REGION FOR IRON EXPLORATION, CENTRAL EAST OF IRAN

Link for citation: Amin Karimi Kalvarzi, Aref Shirazi, Adel Shirazy, Amin Beiranvand Pour, Ardeshir Hezarkhani, Hamed Nazerian, Timkin T.V., . Voroshilov V.G. Separation of magnetic anomalies using fractal method in the Esfordi region for iron exploration, central east of Iran. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 3, рр. 197-209. In Rus.
 The relevance of research is determined by the possibilities of measuring the potential magnetic field, which has self-similar (fractal) properties, as well as a practical tool for prospecting and exploration of iron ores. In the Esfordi area, this method was used by us for the first time to identify, separate and interpret geophysical (magnetic) anomalies. The main aim of this thematic and practical study is the qualitative interpretation of geophysical data, the application of new methods in the prospecting and exploration of mineral deposits, modeling the geological environment and forecasting new promising areas. Object: Esfordi region, Yazd province, Iran. Methods. To obtain additional information about the subsurface, magnetometric data were used with their interpretation by the RTP (reduction to the north magnetic pole) method. For modeling purposes, an artificial sample was made, consisting of a sphere, a cube and a cuboid, and it was found that the fractal method can be used to separate anomalies for unipolar models (cube and cuboid). Results. The results of the study were applied to the Esfordi region, where it was found that at a survey scale of 1:100000, there is a direct relationship between the fractal method and the 3D model, which can be used to locate iron ore mineralization.

Elizabeth Robins's Alaskan Fiction and the Global New South

ABSTRACT: In the summer of 1900, at the height of the Nome gold rush, actress and soon-to-be suffragist Elizabeth Robins traveled to Alaska. Following her return, Robins published two novels and several stories set in the region. Yet even as she capitalized on the popularity of gold rush settings and tropes, Robins's Alaskan fiction consistently undermines the romantic mythology that typically characterizes gold rush narratives, highlighting instead the environmental and human degradation that gold mining entailed. Focusing primarily on her novel The Magnetic North (1904) and the connected story "Monica's Village" (1905), this essay explores how Robins's Alaskan fiction recycles US Southern plantation mythology in order to imagine an alternative form of Alaskan development, one that would transform Alaska's Indigenous population into a racialized labor force to be exploited in ways comparable to African Americans under Jim Crow. Though the environmental conditions of Alaska foreclosed the possibility of traditional plantation agriculture, Robins's fiction maps plantation dynamics onto the forms of mineral extraction transforming the region. In doing so, these texts reveal the pliability of the plantation imaginary as well as the global scope of plantation modernity. This essay argues that the Plantationocene offers a useful framework for reconsidering the intertwined histories of plantation agriculture and mineral extraction. Robins's vision of Alaska as a New South ultimately highlights the ways in which mineral extraction in the Far North follows a pattern established by plantation agriculture throughout the Global South.

Elizabeth Robins's Alaskan Fiction and the Global New South

ABSTRACT: In the summer of 1900, at the height of the Nome gold rush, actress and soon-to-be suffragist Elizabeth Robins traveled to Alaska. Following her return, Robins published two novels and several stories set in the region. Yet even as she capitalized on the popularity of gold rush settings and tropes, Robins's Alaskan fiction consistently undermines the romantic mythology that typically characterizes gold rush narratives, highlighting instead the environmental and human degradation that gold mining entailed. Focusing primarily on her novel The Magnetic North (1904) and the connected story "Monica's Village" (1905), this essay explores how Robins's Alaskan fiction recycles US Southern plantation mythology in order to imagine an alternative form of Alaskan development, one that would transform Alaska's Indigenous population into a racialized labor force to be exploited in ways comparable to African Americans under Jim Crow. Though the environmental conditions of Alaska foreclosed the possibility of traditional plantation agriculture, Robins's fiction maps plantation dynamics onto the forms of mineral extraction transforming the region. In doing so, these texts reveal the pliability of the plantation imaginary as well as the global scope of plantation modernity. This essay argues that the Plantationocene offers a useful framework for reconsidering the intertwined histories of plantation agriculture and mineral extraction. Robins's vision of Alaska as a New South ultimately highlights the ways in which mineral extraction in the Far North follows a pattern established by plantation agriculture throughout the Global South.

On the Determination of the Geographic North on Archeological Plans in Connection with the Problem of the Quality of Geographic Education

The publication is dedicated to the memory of N.A. Bogdanov (1954-2020), Doctor of Geography, Leading Researcher of the Laboratory of Geomorphology of the Institute of Geography of the Russian Academy of Sciences, who participated in the preparation of materials and publication of abstracts on March 1, 2020. The article raises the question of the need for the development of universal geographic education, which forms the cultural appearance of a person and the scientific picture of the world of our era. The consequences of typical technical errors in working with the topographic plan are analyzed: the sides of the horizon are not indicated; north is specified with an error; the original high-quality materials were used incorrectly; magnetic north is indicated, but the year of the topographic survey is not indicated; supplemented topographic maps are superimposed on the historically previous topographic base. The changes in the current situation, according to the authors, are facilitated by the following tasks: to increase the number of hours of teaching geography at school; pay more attention to practical orienteering exercises; expand the selection of popular geographic literature to raise public awareness of the possibilities of classical methods and fundamental achievements of modern geography; and some others. Keywords: cartography, education, archaeological sites, interpretation, information

Evidence for magnetic orientation in Clethrionomys glareolus in a water maze assay (Rodentia: Cricetidae)

A long-term issue when studying magnetic orientation is the replicability of the experiments conducted in different laboratories. Attempts to replicate experiments have failed many times. After our previous study where we successfully found magnetoreception in the bank vole (Clethrionomys glareolus) we decided to replicate the water maze experiment. The bank voles were trained and tested in a four-arm “plus” maze in different magnetic conditions – natural magnetic field and three magnetic fields with shifted position of magnetic north (+90°, +180°, and +270°). The tested bank voles showed learned directional preference in the water maze therefore we can consider this species magnetoreceptive, able to use magnetic field for orientation. However, the results were more scattered than in the study with C57BL/6J mice. This difference probably corresponds with the absence of the protection against disturbing radio frequency magnetic fields during experiment, as well as, with the behavioural differences of free-living voles and laboratory mice.

Evidence of the Hall Effect Providing the Core Field inside a Magnetic Flux Rope in an Antiparallel Magnetic Reconnection

The observations from the Magnetospheric Multiscale mission on 2015 November 12 showed the existence of tripolar Hall magnetic fields north of the X line in a quasi-antiparallel reconnection at the dayside of the magnetopause. The bipolar variation in the normal component of the magnetic field inside the middle polar region of the tripolar Hall fields indicated the presence of an ion-scale magnetic flux rope. The coexistence of Hall fields and a magnetic flux rope provides the first evidence that the Hall effect in quasi-antiparallel magnetic reconnection can generate the core field inside a magnetic flux rope. There is one dip in the core field of the observed magnetic flux rope. We interpret the core field and the dip with the Hall effect associated with sequential multiple-X-line reconnection. The results of this study shed light on the mechanism of the generation of the core field inside the magnetic flux rope.

Subsurface structural characterization as deduced from potential field data—West Beni Suef, Western Desert, Egypt

The goal of present study is determining subsurface structural elements by analyzing geomagnetic data sets aiming to examine their impacts on geological surface structures characterizing the western region in Beni-Suef Governorate, Western Desert, Egypt. A land-magnetic survey is conducted by two exceedingly sensitive proton magnetometers to measure the total intensity of geomagnetic field at the region under investigation. The measurements of regional gradients and time variation were applied to get the required reduction of daily variation. The regional expansions of subsurface structural units were obtained after applying the reduction to north magnetic pole (RTP) method to the corrected magnetic data acquired from land-magnetic survey along with Bouguer maps (1:100,000 scale and 1-mGal contouring interval). Regional-residual technique was applied depending on the power spectrum analysis. Moreover, the edge detection approach is conducted to depict the structures and subsurface hidden anomalies. Different handling processes were applied for acquired land magnetic datasets such as Euler deconvolution and trend analysis. The results of current study revealed that four significant structural forces across the N-S, NW–SE, NE-SW, and E-W directions affected the region. Estimating the basement depth was accomplished using a number of spectral analysis techniques. The values of estimated depths are used for creating a basement relief map. Moreover, the achieved results show that depths to the basement at the region under study vary between 2.3 and 4.7 km.

A sensor fusion approach to MARG module orientation estimation for a real-time hand tracking application

This paper introduces a new algorithm (Gravity & Magnetic North Vector correction — Double SLERP, or “GMV-D”) to estimate the orientation of a MEMS Magnetic/Angular-Rate/Gravity (MARG) sensor module using sensor fusion in the context of a real-time hand tracking application, for human–computer interaction purposes.Integrated MEMS MARG modules are affordable, small, light and consume minimal power. As such, there is interest in using them for monitoring the orientation of various body segments, to which they can be attached (e.g., the finger segments of a gloved hand). However, each of the 3 types of signals they provide has proven insufficient to yield robust orientation estimates, particularly in regions of space where the geomagnetic field is distorted. The significance (main contribution) of the approach we present is the computation of a final orientation estimate that uses all the signals generated by inexpensive (e.g., less than 20 USD, in large quantities) integrated MEMS MARG modules but weighs their contributions with simple, real-time-updatable parameters that prevent erroneous corrections when the pre-conditions for their valid use are not met. This will enable the use of inexpensive integrated MEMS MARG modules for hand tracking applications in human–computer interaction and other areas of work where tracking the orientation of body segments in real-time is important.In each iteration, GMV-D defines an initial orientation estimate from integration of gyroscopic signals (“dead reckoning”), and also calculates accelerometer-based and magnetometer-based corrections. These corrections are defined on the assumptions that the module is near static and affected by an undistorted geomagnetic field.Because these assumptions are seldom fully met simultaneously, the information fusion challenge is to apply each correction only to the extent that its corresponding pre-conditions are met, as inappropriate corrections will introduce significant error in the future orientation estimates. To achieve this, GMV-D develops an accelerometer correction trustworthiness parameter, 0 ≤α≤ 1, and a magnetometer correction trustworthiness parameter, 0 ≤μ≤ 1, both of which are updated on a sample-by-sample basis and are available at each iteration of the algorithm. The information fusion phase of the algorithm implements the corrections in a two-tiered application of Spherical Linear Interpolation (SLERP) of the quaternions representing the initial dead reckoning estimate and the available corrections, scaled according to their corresponding levels of trustworthiness.GMV-D was evaluated in comparison to 2 other orientation correction approaches (Kalman Filtering and GMV-S) and contrasted with 2 contemporary complementary filter approaches (Madgwick , Mahony). The results confirm that GMV-D displayed better orientation estimation performance when the algorithms operated in an area with known distortion of the geomagnetic field.

Reconstruction of the Virtual Geomagnetic Pole (VGP) path at high latitude for the last 22 kyr: The role of radial field flux patches as VGP attractor

Reconstruction of geomagnetic field changes has a strong potential to complement geodynamo modeling and improve the understanding of Earth's core dynamics. Recent works based on geomagnetic measurements pointed out that over the last two decades the position of the north magnetic pole has been largely determined by the influence of two competing flux lobes under Canada and Siberia.In order to understand if the waxing and waning of magnetic flux lobes have driven the path of geomagnetic paleopoles in the past, we present an augmented and updated record of the chronology and paleosecular variation of geomagnetic field for the last 22 kyr derived from sedimentary cores collected along the north-western margin of Barents Sea and western margin of Spitsbergen (Arctic). The path of the virtual geomagnetic pole (VGP) has been reconstructed over this time period and compared with the maps of the radial component of the geomagnetic field at the core-mantle boundary, obtained from the most recent models. The VGP path includes centuries during which the VGP position is stable and centuries during which its motion accelerates. We recognize both clockwise and counterclockwise VGP paths, mostly developing inside the surface projection of the inner core tangent cylinder in the Arctic region. The VGP path seems to follow the appearance of Br patches of normal magnetic flux, especially those located under Siberia and Canada areas, but also those that may cause peculiar paleomagnetic features such as the Levantine Iron Age Anomaly.

Najstaršia banská mapa ešte raz: jej georeferencovanie a analýza

The oldest known map of a mine in what is now Slovakia was drawn in 1568 and represents an adit named Gottes gab. The location of the mine is given only by the description “auf der Jeraba” (at Jarabá in the Low Tatras) and the exact whereabouts of the mine was unknown until recently. This article describes the methodology used to locate the adit using other mining maps of this area produced in the 18th century, which depicted some landmarks making geolocation possible – a toponym, segments of some country roads and two other mine entrances. The mining maps were georeferenced using historical geography, field research and a detailed DTM. The correctness of the georeferencing was validated by checking the scale (using the scale bar) and rotation parameters (comparing the magnetic north indications on the maps to the models of the historical magnetic declination). The second part of the paper contains a new interpretation of a unique feature of the Gottes gab map – a survey field book in tabular form, previously analyzed by Bílek (1967). Using statistical analysis we propose the most feasible formula for calculation of the survey line coordinates from the data table. The problems in this reconstruction of the mine survey line are explained using newer, 18th century maps of the same mine.

Secular variations on the North American tectonic plate

Based on the results of geomagnetic observatories located near the North magnetic pole and in the middle latitudes of the North American tectonic plate, the secular variations (SV) of the Earth’s geomagnetic field have been studied. The influence of solar activity on SV on the North American plate has been shown.
 The author has identified the SV source of non-dipole origin with a period of about 22 years. The source did not affect SV in the XX—XXI cycle of solar activity probably due to the influence of the SV jerk, but it showed itself well in the XXII—XXIV cycles of solar activity. It is demonstrated that the influence of the SV source increases with increasing latitude of the observatory and is almost imperceptible at low latitudes.
 According to the Minuk observatory and others, a 100-year cycle of age-related variation has been identified — the early 20th century: a maximum took place in the 1960s and cycle termination was in 2013.
 Following the observatories located on the eastern part of the plate, the SV acceleration triggered by the influence of the Atlantic focus has been calculated. The research identifies that the «activation» of the SV Atlantic focus occurs with an expansion in the number of recurrent geomagnetic storms, which is evidenced in odd cycles of solar activity (the VMS direction from the Sun).
 According to observatories located near the Pacific Plate (west coast of North America), the impact of the Atlantic focus on SV is not as pronounced as in the eastern part. However, there is an influence of the non-dipole SV source depending on the observatory’s latitude and solar activity.

Can machine learning reveal precursors of reversals of the geomagnetic axial dipole field?

SUMMARY It is well known that the axial dipole part of Earth’s magnetic field reverses polarity, so that the magnetic North Pole becomes the South Pole and vice versa. The timing of reversals is well documented for the past 160 Myr, but the conditions that lead to a reversal are still not well understood. It is not known if there are reliable ‘precursors’ of reversals (events that indicate that a reversal is upcoming) or what they might be. We investigate if machine learning (ML) techniques can reliably identify precursors of reversals based on time-series of the axial magnetic dipole field. The basic idea is to train a classifier using segments of time-series of the axial magnetic dipole. This training step requires modification of standard ML techniques to account for the fact that we are interested in rare events—a reversal is unusual, while a non-reversing field is the norm. Without our tweak, the ML classifiers lead to useless predictions. Perhaps even more importantly, the usable observational record is limited to 0–2 Ma and contains only five reversals, necessitating that we determine if the data are even sufficient to reliably train and validate an ML algorithm. To answer these questions we use several ML classifiers (linear/non-linear support vector machines and long short-term memory networks), invoke a hierarchy of numerical models (from simplified models to 3-D geodynamo simulations), and two palaeomagnetic reconstructions (PADM2M and Sint-2000). The performance of the ML classifiers varies across the models and the observational record and we provide evidence that this is not an artefact of the numerics, but rather reflects how ‘predictable’ a model or observational record is. Studying models of Earth’s magnetic field via ML classifiers thus can help with identifying shortcomings or advantages of the various models. For Earth’s magnetic field, we conclude that the ability of ML to identify precursors of reversals is limited, largely due to the small amount and low frequency resolution of data, which makes training and subsequent validation nearly impossible. Put simply: the ML techniques we tried are not currently capable of reliably identifying an axial dipole moment (ADM) precursor for geomagnetic reversals. This does not necessarily imply that such a precursor does not exist, and improvements in temporal resolution and length of ADM records may well offer better prospects in the future.