Axial Dipole Research Articles

The basic solar wind speed distribution and its sunspot cycle variations

In this paper, it is suggested that the latitudinal solar wind speed observed by the Ulysses spacecraft during the lowest solar activity (when both the ecliptic and magnetic equators coincide) may be identified as the basic speed distribution throughout the solar cycle. We demonstrate this suggestion by rotating this particular Ulysses distribution counterclockwise up to 70° in accordance with the rotation of the equivalent dipole axis during active periods of the cycle. The corresponding magnetic equator in the Carrington map latitude-longitude (27 days) becomes quasi-sinusoidal with respect to the ecliptic equator. The quasi-sinusoidal magnetic equator on the Carrington map and its modification associated with the degree of sunspot activities can explain the two high speed peaks (750–800 km/s) and the two lowest speed (350 km/s) during 27-day solar rotation periods, most clearly recognizable after the sunspot peak period. Thus, it may be not necessary to consider coronal holes or open regions as the source of high speed streams. In fact, this particular (lowest solar activity) Ulysses distribution may represent the speed distribution pattern by the basic generation process of the solar wind itself.

Paleomagnetism, rock magnetism and age determination of effusive and explosive Holocene volcanism in the Momotombo-Managua-Masaya region, Nicaragua

The Central America Volcanic Arc shows an intense and continuous volcanic activity spanning the last 10 ky because of the subduction processes parallel to the Middle America Trench. Several volcanic events have occurred during the Plio-Holocene, along the coastal Nicaraguan region, characterized either by explosive or effusive activity. Volcanic deposits were emplaced at high temperatures and have similar basaltic-andesitic composition suggesting a long-lived magma chamber but emplaced and cooled by different mechanisms. We present paleodirectional and paleointensity results of four lava flows, and the paleointensity recorded on different pyroclastic deposits in the Managua-Masaya region, western Nicaragua. For each, we characterize the rock magnetic properties as a function of temperature and magnetic field. Absolute paleointensity experiments estimated a mean range from 38.6 to 52.9 μT; and a mean virtual axial dipole moment from 9.4 × 1022 Am2 to 12.8 × 1022 Am2. Two paleomagnetic ages were determined for two cooling units: (1) the Masaya Caldera Walls with an age range of 8580–8535 BP, and (2) a dating for a lava flow from Momotombo Volcanic Complex estimated of 1500–1600 CE. These results are consistent with the expected values according to the actual paleosecular variation global models, and with the regional stratigraphy and historical ages. The high reliability of paleointensity determination from these pyroclastic deposits and lava flows suggest that both are suitable for paleomagnetic dating. Finally, an accurate chronology of the volcanic events, will improve the understanding of the evolution of the volcanism and their implications for volcanic risk on the region. This knowledge will help to decrease the considerable hazard for the population on the surrounding areas.

Paleomagnetism of the Taseeva Group (Yenisei Ridge): on the Issue of the Geomagnetic Field Configuration at the Precambrian–Phanerozoic Boundary

Abstract —We report results of a detailed study of the paleomagnetic record in the sedimentary rocks of the Taseeva Group of the Yenisei Ridge in three typical sections in the lower courses of the Angara, Taseeva and Irkineeva rivers. Our results confirm that the geomagnetic field was in an anomalous state at the Precambrian–Phanerozoic boundary. It is well known that Ediacaran rocks in general have preserved several different paleomagnetic directions that do not conform to the geocentric axial dipole model. For example, Siberian sections display two equally valid groups of paleopoles that cause many debates over the geometry of the geomagnetic field and whether any of the components correspond to its dipole configuration. The paleomagnetic record we studied is unique in that the rocks of the Chistyakovka and Moshakovka formations have captured both these components, which is factual evidence of a synchronous existence of two sources. To explain these findings, we propose an original hypothesis in which the bipolar component that is widely present in the rocks and corresponds to the Madagascar group of paleomagnetic poles is associated to the field of the geocentric axial dipole. The less widespread monopolar component corresponding to the Australian–Antarctic group of poles is reflective of a stationary anomalous source. The recording of this source became possible due to the abrupt decrease in the strength of the virtual dipole moment that probably was at its lowest during the accumulation of the Chistyakovka and Moshakovka formations. The new paleomagnetic pole calculated for the bipolar component – 39.2°N, 61.1°E – plots on the apparent polar wander path for Siberia and can be considered a key determination for the age ~570 Ma.

Reanalysis of the Spin Direction Distribution of Galaxy Zoo SDSS Spiral Galaxies

The distribution of the spin directions of spiral galaxies in the Sloan Digital Sky Survey has been a topic of debate in the past two decades, with conflicting conclusions reported even in cases where the same data were used. Here, we follow one of the previous experiments by applying the SpArcFiRe algorithm to annotate the spin directions in an original dataset of Galaxy Zoo 1. The annotation of the galaxy spin directions is carried out after the first step of selecting the spiral galaxies in three different manners: manual analysis by Galaxy Zoo classifications, by a model-driven computer analysis, and with no selection of spiral galaxies. The results show that when spiral galaxies are selected by Galaxy Zoo volunteers, the distribution of their spin directions as determined by SpArcFiRe is not random, which agrees with previous reports. When selecting the spiral galaxies using a model-driven computer analysis or without selecting the spiral galaxies at all, the distribution is also not random. Simple binomial distribution analysis shows that the probability of the parity violation to occur by chance is lower than 0.01. Fitting the spin directions as observed from the Earth to cosine dependence exhibits a dipole axis with statistical strength of 2.33 σ to 3.97 σ . These experiments show that regardless of the selection mechanism and the analysis method, all experiments show similar conclusions. These results are aligned with previous reports using other methods and telescopes, suggesting that the spin directions of spiral galaxies as observed from the Earth exhibit a dipole axis formed by their spin directions. Possible explanations can be related to the large-scale structure of the universe or to the internal structure of galaxies. The catalogs of annotated galaxies generated as part of this study are available.

Lagrangian descriptor and escape time as tools to investigate the dynamics of laser-driven polar molecules.

We consider the nonlinear dynamics of a diatomic polar molecule under a linearly polarized laser field. We assume a model in which the molecule dipole is coupled with a time-dependent electric field. This system presents a bound energy region where the atoms are bound, and a free-energy region where the atoms are dissociated. Due to the nonalignment between the dipole axis and the laser direction, and the time dependence of the external field, this system presents two and a half degrees of freedom, namely the vibrational degree, the rotation degree, and the time. To investigate the system dynamics, instead of using the Poincaré surface-of-section technique, we propose the use of the Lagrangian descriptor associated with the escape times. The Lagrangian descriptor is a quantity that reveals complex structures in the phase space, whereas the escape times are the time span in which a trajectory is initially in the bound region before escaping to the unbound region. The combination of these two quantities allows us to distinguish between real stability regions from other complex structures, including stickiness regions, and a different formation, which we call escape islands. With the help of these tools, we find that for high-field amplitudes the inclusion of rotation leads to an increase of the stability regions, which implies a decrease of the dissociation in comparison with the one-dimensional case.

Characteristics of the Matuyama‐Brunhes Magnetic Field Reversal Based on a Global Data Compilation

AbstractMagnetic field reversals are irregular events in Earth's history when the geomagnetic field changes its polarity. Reversals are recorded by spot and continuous remanent magnetization data collected from lava flows and marine sediments, respectively. The latest field reversal, the Matuyama‐Brunhes reversal (MBR), is better covered by paleomagnetic data than prior field reversals, hence providing an opportunity to understand the physical mechanisms. Despite the quantity of data, a full understanding of the MBR is still lacking. The evolution of the MBR in time and space is explored in this work by compiling a global set of paleomagnetic data, both from sediments and volcanic rocks, which encompass the period 900–700 ka. After careful evaluation of data and dating quality, regional and global stacks of virtual axial dipole moment (VADM), virtual geomagnetic pole (VGP), and paleosecular variation index (Pi) are constructed from the sediment records using bootstrap resampling. Individual VADMs and VGPs calculated from lavas are compared to these stacks. Four phases of full‐vector field instability are observed in these stacks over the period 800–770 ka. The first three phases, observed at 800–785 ka, reflect a rapid weakening of the field coupled with low VGP latitude, after which the field returned to the reverse polarity of the Matuyama chron. The fourth phase, lasting from 780 to 770 ka, is when the field reversal process completed, such that the field entered the Brunhes normal polarity state. These findings point to a complex reversal process lasting ∼30 Kyr, with the reversal ending at ∼770 ka.

Multipole expansion of the local expansion rate

We design a new observable, the expansion rate fluctuation $\ensuremath{\eta}$, to characterize deviations from the linear relation between redshift and distance in the local universe. We also show how to compress the resulting signal into spherical harmonic coefficients in order to better decipher the structure and symmetries of the anisotropies in the local expansion rate. We apply this analysis scheme to several public catalogs of redshift-independent distances, the Cosmicflows-3 and Pantheon datasets, covering the redshift range $0.01<z<0.05$. The leading anisotropic signal is stored in the dipole. Within the standard cosmological model, it is interpreted as a bulk motion ($307\ifmmode\pm\else\textpm\fi{}23\text{ }\text{ }\mathrm{km}/\mathrm{s}$) of the entire local volume in a direction aligned at better than 4 degrees with the bulk component of the Local Group (LG) velocity with respect to the cosmic microwave background (CMB). This term alone, however, provides an overly simplistic and inaccurate description of the angular anisotropies of the expansion rate. We find that the quadrupole contribution is non-negligible ($\ensuremath{\sim}50%$ of the anisotropic signal), in fact, statistically significant, and signaling a substantial shearing of gravity in the volume covered by the data. In addition, the 3D structure of the quadrupole is axisymmetric, with the expansion axis aligned along the axis of the dipole. Implications for the determination of the ${H}_{0}$ parameter are discussed. We find that Hubble constant estimates may show variation as high as $\mathrm{\ensuremath{\Delta}}{H}_{0}=(4.1\ifmmode\pm\else\textpm\fi{}1.1)\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ between antipodal directions along the dipole axis. In the case of the Pantheon sample, this systematic difference is reduced to $\mathrm{\ensuremath{\Delta}}{H}_{0}=(2.4\ifmmode\pm\else\textpm\fi{}1.1)\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ once model-dependent correction for peculiar velocity flows are implemented. Notwithstanding, the axial anisotropy in the general direction of the CMB dipole is still detected. We thus show how to optimally subtract redshift anisotropies from Pantheon data in a fully model-independent way by exploiting the $\ensuremath{\eta}$ observable. As a result, the value of the best fitting ${H}_{0}$ is systematically revised upwards by nearly $0.7\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ (about $2\ensuremath{\sigma}$) compared to the value deduced from the Hubble diagram using the uncorrected observed redshift. The goodness of fit is also improved.

Numerical study of rotor unsteady forces and noise due to ingestion of grid-generated turbulence

In many aeronautics and marine applications, the unsteady forces generated by propulsion rotors due to turbulence ingestion are a significant source of noise and create serious concerns. The understanding of rotor turbulence ingestion and the rotor noise generation mechanisms is vital to achieve an optimal design or apply noise control strategy. The current study is the first attempt to numerically investigate an underwater rotor ingesting grid-generated turbulence by large eddy simulation combined with the Ffowcs-Williams and Hawkings equation. The flow characteristics of two directly simulated turbulence grids with a mesh spacing of 4 and 6 in. are investigated and proved to be adequate for the rotor turbulence ingestion study. The simulated unsteady force spectra of the rotor show better agreement with the experimental results in terms of amplitudes and frequency ranges of the first haystack and broadband components compared to previous theoretical and numerical studies. The unsteady forces and noise of the rotor downstream of the 4-in. grid are slightly higher than those downstream of the 6-in. grid. A far-field noise prediction approach based on the time derivatives of the rotor axial and radial unsteady forces are investigated and validated. The far-field noise spectra and the rotor noise directivities predicted by the time derivative approach agree well with the Ffowcs-Williams and Hawkings equation in the main frequency range of underwater rotor noise. The noise directivities are found to be dominated by axial force related dipole sources.

Archaeomagnetism in the Levant and Mesopotamia Reveals the Largest Changes in the Geomagnetic Field.

Our understanding of geomagnetic field intensity prior to the era of direct instrumental measurements relies on paleointensity analysis of rocks and archaeological materials that serve as magnetic recorders. Only in rare cases are absolute paleointensity data sets continuous over millennial timescales, in sub-centennial resolution, and directly dated using radiocarbon. As a result, fundamental properties of the geomagnetic field, such as its maximum intensity and rate of change have remained a subject of lively discussion. Here, we place firm constraints on these two quantities using Bayesian modeling of well-dated archaeomagnetic intensity data from the Levant and Upper Mesopotamia. We report new data from 23 groups of pottery collected from 18 consecutive radiocarbon-dated archaeological strata from Tel Megiddo, Israel. In the Near East, the period of 1700-550BCE is represented by 84 groups of archaeological artifacts, 55 of which were dated using radiocarbon or a direct link to clear historically dated events, providing unprecedented sub-century resolution. Moreover, stratigraphic relationships between samples collected from multi-layered sites enable further refinement of the data ages. The Bayesian curve shows four geomagnetic spikes between 1050 and 600BCE, with virtual axial dipole moment (VADM) reaching values of 155-162ZAm2, much higher than any prediction from geomagnetic field models. Rates of change associated with the four spikes are ∼0.35-0.55μT/year (∼0.7-1.1ZAm2/year), at least twice the maximum rate inferred from direct observations spanning the past 180years. The increase from 1750 to 1030BCE (73-161ZAm2) depicts the Holocene's largest change in field intensity.

Examining statistical isotropy of CMB low multipoles from Planck PR4 data

Low multipoles (l) in cosmic microwave background (CMB) temperature anisotropies have shown some ‘peculiarities’ when examined since the release of the full sky CMB maps, using a variety of tests. In this paper, we concern ourselves with the very first peculiarities seen in CMB data viz., a breakdown of statistical isotropy in the form of axiality and planarity of these low-l modes, and preferred alignments among them. We scrutinize the latest CMB data from ESA's Planck mission, PR4, to evaluate the current status of these deviations. We employ the Power tensor method which allows an invariant characterization of the distribution of power in a given multipole, and apply it to probe the first sixty multipoles i.e., l=2 to 61. We find that there are significant number of modes that are intrinsically anisotropic with a cumulative probability of 0.3%. However since the planarity study reveals that those modes that are unusually planar are subset of these anisotropic modes, we conclude that they may not be intrinsically planar. The quadrupole is still well aligned with the octopole. Besides, l=3, higher multipoles aligned with quadrupole are found to be insignificant. Interestingly, the collective alignment axis of the first sixty multipoles is found to be broadly closer to the axis of dipole, quadrupole, octopole and other modes aligned with l=2.

Optical conductivity of the threefold Hopf semimetal

A multifold Hopf semimetal is a topological point node semimetal possessing an anisotropy in the internal electronic structure, e.g., the dipole structure of the Berry curvature. In this paper, the unique features of threefold Hopf semimetals in terms of the optical conductivity are theoretically investigated with a minimal theoretical model by using linear response theory for a linearly polarized photon. The frequency spectrum of the optical conductivity shows an anisotropic dependence on the polarization angle of the incident photon even if the electronic band structure is completely isotropic. The longitudinal optical conductivity linearly depends on the photon frequency and possesses steplike changes in the frequency spectrum. The anisotropic electronic structure has a varying number of steps with the orientation of the photon polarization axis. We reveal that the anisotropy is attributed to symmetries preserving the point node in threefold Hopf semimetals and that the threefold fermion in the Hopf semimetal is qualitatively different from so-called spin-1 fermion. The linearly polarized photon also induces a Hall current, but it vanishes with the photon polarization axis parallel to the Berry dipole axis. The numerical calculations show that these characteristic features can be observed even with a nonzero temperature and disorder.

MCADAM: A Continuous Paleomagnetic Dipole Moment Model for at Least 3.7 Billion Years

AbstractUnderstanding the evolution of Earth's magnetic field can provide insights into core processes and can constrain plate tectonics and atmospheric shielding. The absolute paleointensity database PINT provides a curated repository of site mean (i.e., cooling unit), estimates of the strength of the magnetic field. We present a minor update to the PINT database to version 8.1.1 by adding 295 records from 34 studies. The PINT database is used to define a continuous model of the dipole field, using an approach combining non‐parametric and Monte Carlo (MC) resampling termed Monte Carlo Axial Dipole Average Model (MCADAM). Three dipole field strength models spanning 50 ka to 3.7–4.2 Ga (MCADAM.1a‐c) are presented, reflecting three tiers of increasingly more stringent data selection. The MCADAM models allow for the estimation of the magnetic standoff distance, constraining the shielding of Earth's atmosphere against solar wind erosion provided by the geodynamo.

Further evidence of unstable reverse polarity geomagnetic field across the Olduvai subchron: paleomagnetic and multispecimen paleointensity study on Khertvisi lava flows (Lesser Caucasus)

Goguitchaichvili et al. (Physics of the Earth and Planetary Interiors, doi.org/10.1016/j.pepi.2020.106641, 2021) reported a detailed rock-magnetic and paleointensity study of a Lesser Caucasus lava sequence comprised between 1.93 ± 0.09 and 1.78 ± 0.11 Ma. Reverse polarity magnetization determined for 20 consecutive lava flows permitted to suggest that the Olduvai subchron is probably disrupted by a short reverse-polarity episode. No paleointensity was obtained because of thermally unstable samples. Here, we report a detailed rock-magnetic, paleomagnetic, and multispecimen parallel differential pTRM absolute paleointensities performed on the nearby parallel Khertvisi lava succession. New isotopic age determinations indicate that the lavas of the Khertvisi section erupted in the Early Pleistocene, at the boundary of Gelasian and Calabrian ages in a time span of 1.88 ± 0.10 to 1.71 ± 0.12 Ma. All lava flows yielded well-defined reverse polarity magnetization with site mean directions Inc. = −56.1°, Dec = 189.5°, N = 20 (lava flows), α95 = 2.3°, k = 187. These directions are close to the Toloshi mean paleodirections, and both slightly deviate clockwise from the geocentric axial dipole and expected Plio-Quaternary directions. The values of the virtual geomagnetic pole (VGP) scatter parameters indicate that the studied sequence was formed during a very short time, most probably insufficient to average paleosecular variation. The multispecimen methodology provided a relatively low paleointensity for most analyzed lava flows, comparable to the transitional field intensity in Georgia during the Bruhnes and Matuyama chrons. These results definitively confirm a rather unstable, reverse polarity geomagnetic field regime across the Olduvai normal superchron. Thus, we propose to consider the Khertvisi section as the firm, volcanic evidence of Olduvai's short-lived geomagnetic event.

The role of slow magnetostrophic waves in the formation of the axial dipole in planetary dynamos

The preference for the axial dipole in planetary dynamos is investigated through the analysis of wave motions in spherical dynamo models. Our study focuses on the role of slow magnetostrophic waves, which are generated from localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces. Since the slow waves are known to intensify with increasing field strength, simulations in which the field grows from a small seed towards saturation are useful in understanding the role of these waves in dynamo action. Axial group velocity measurements in the energy-containing scales show that fast inertial waves slightly modified by the magnetic field and buoyancy are dominant under weak fields. However, the dominance of the slow waves is evident for strong fields satisfying ∣ωM/ωC∣∼ 0.1, where ωM and ωC are the frequencies of the Alfvén and inertial waves respectively. A MAC wave window of azimuthal wavenumbers is identified in which helicity generation by the slow waves strongly correlates with dipole generation. Analysis of the magnetic induction equation suggests a poloidal–poloidal field conversion in the formation of the dipole. Finally, the attenuation of slow waves may result in polarity reversals in a strongly driven Earth's core.

Molecular sensors producing circularly polarized luminescence responses

Circularly polarized luminescence (CPL) refers to spontaneous emission with the oscillation axis of the emission's electric dipole rotating either right handedly or left handedly along the propagation axis. CPL provides a unique principle in luminescence visualization of target analytes: both the direction and magnitude of light polarization are sensitive to an asymmetric environment around a luminophore, which enables chirality sensing. In addition, CPL spectra are usually less complex than electric circular dichroism spectra because they emerge only from the lowest excited state. To exploit these benefits, researchers have vigorously developed CPL probes. This minireview provides the basic principles for creating molecular CPL activity, including asymmetric exciton coupling and helical intramolecular charge transfer. Emphasis is placed on molecular design. Analyte interactions can perturb the magnitude, reverse the polarization direction, or shift the peak wavelength of CPL, thereby enabling tractable strategies for creating CPL sensors. This minireview outlines selected examples of CPL sensors for physical stimuli, including changes in external magnetic fields, solvent polarity, and temperature. Probes capable of detecting chemical species, such as protons, metal ions, anions, amino acids, nucleosides and DNA, reactive oxygen species, and humidity, are also highlighted. These examples demonstrate the unique sensing utility of CPL sensors. We hope that this minireview will stimulate future research interest toward developing advanced CPL sensors with applications in bioimaging.

Paleomagnetism and paleolatitude of igneous drill core samples from the Izu-Bonin forearc and implications for Philippine Sea plate motion

The Philippine Sea plate is an integral part of the east Asian plate mosaic but its past motions can only be reconstructed from paleomagnetic data. Moreover, because the plate is largely submarine, few fully-oriented paleomagnetic data are available. International Ocean Discovery Program (IODP) Expedition 352 cored at four sites on the Izu-Bonin forearc, penetrating ∼1170 m of forearc igneous crust radiometrically dated at ∼51 Ma. Paleomagnetic measurements on 361 samples produced paleo-inclination data that were used to estimate paleolatitude. Twenty five independent magnetic units give a paleocolatitude of 90.1° ±4.4° (2σ uncertainty), implying a paleolatitude exactly on the equator. Unit variance agrees with global paleosecular variation models, implying that these variations have been properly sampled and averaged. The paleolatitude implies northward drift of ∼28°, which agrees with other Izu-Bonin forearc sites of similar age. A slight difference in northward drift with southern Philippine Sea plate sites is consistent with plate rotation. Certain parts of the cored sections yield samples that were remagnetized to the present geocentric axial dipole inclination after ∼30 Ma, implying a tectonic event of unclear origin.

Paleointensity Estimates From the Pleistocene of Northern Israel: Implications for Hemispheric Asymmetry in the Time‐Averaged Field

AbstractTwenty‐two sites, subjected to an IZZI‐modified Thellier‐Thellier experiment and strict selection criteria, recover a paleomagnetic axial dipole moment (PADM) of 62.2 ± 30.6 ZAm2 in Northern Israel over the Pleistocene (0.012–2.58 Ma). Pleistocene data from comparable studies from Antarctica, Iceland, and Hawaii, re‐analyzed using the same criteria and age range, show that the Northern Israeli data are on average slightly higher than those from Iceland (PADM = 53.8 ± 23 ZAm2, n = 51 sites) and even higher than the Antarctica average (PADM = 40.3 ± 17.3 ZAm2, n = 42 sites). Also, the data from the Hawaiian drill core, HSDP2, spanning the last half million years (PADM = 76.7 ± 21.3 ZAm2, n = 59 sites) are higher than those from Northern Israel. These results, when compared to Pleistocene results filtered from the PINT database (www.pintdb.org) suggest that data from the Northern hemisphere mid‐latitudes are on average higher than those from the southern hemisphere and than those from latitudes higher than 60°N. The weaker intensities found at high (northern and southern) latitudes therefore, cannot be attributed to inadequate spatiotemporal sampling of a time‐varying dipole moment or low quality data. The high fields in mid‐latitude northern hemisphere could result from long‐lived non‐axial dipole terms in the geomagnetic field with episodes of high field intensities occurring at different times in different longitudes. This hypothesis is supported by an asymmetry predicted from the Holocene, 100 kyr, and 5 million year time‐averaged geomagnetic field models.

Analysis of spin directions of galaxies in the DESI Legacy Survey

ABSTRACT The DESI Legacy Survey is a digital sky survey with a large footprint compared to other Earth-based surveys, covering both the Northern and Southern hemispheres. This paper shows the distribution of the spin directions of spiral galaxies imaged by DESI Legacy Survey. A simple analysis of dividing nearly 1.3 × 106 spiral galaxies into two hemispheres shows a higher number of galaxies spinning counterclockwise in the Northern hemisphere, and a higher number of galaxies spinning clockwise in the Southern hemisphere. That distribution is consistent with previous observations, but uses a far larger number of galaxies and a larger footprint. The larger footprint allows a comprehensive analysis without the need to fit the distribution into an a priori model, making this study different from all previous analyses of this kind. Fitting the spin directions of the galaxies to cosine dependence shows a dipole axis alignment with probability of P < 10−5. The analysis is done with a trivial selection of the galaxies, as well as simple explainable annotation algorithm that does not make use of any form of machine learning, deep learning, or pattern recognition. While further work will be required, these results are aligned with previous studies suggesting the possibility of a large-scale alignment of galaxy angular momentum.

A summary of paleomagnetic secular variation and excursions for the last 380 ky of the Brunhes normal polarity Chron

This study develops composite high-resolution, full-vector PSV records for the last 380 ka from three regions associated with ODP Leg 172 in the western North Atlantic Ocean. These records identify 207 inclination features and 196 declination features that are common to all three regions. The average sediment accumulation rates are ~25 cm/ky, which produce sampling intervals of ~100–200 years. Each region has been dated by a combination of oxygen isotope stratigraphy and carbonate stratigraphy. We also have developed relative paleointensity records from all three regions that have 34 features in common. The paleointensity features can also be correlated to the PISO-1500 global paleointensity record of Channell et al. (2009) and provide an independent chronostratigraphy. The directions have near Gaussian distributions with inclinations averaging about 6° lower than axial dipole expectation due to the ΔI anomaly. The intensities also have a near Gaussian distribution, but have some more low intensities than expected. There is reproducible evidence for 7 excursions in these records with good waveform information. The excursions last from ~900 to ~8400 years. Five of the excursions are Class I excursions with out-of-phase inclination and declination variability that produces clockwise or counter-clockwise circularity. Two of the excursions (Blake Event, 8α Excursion) are Class II excursions with in-phase inclination and declination variability. Both of these excursions should be considered local reversals due to their very fast (<200 year) in-phase directional movement to reversed polarity directions that hover there before returning quickly to normal polarity directions. We have complete full-vector PSV records that surround each of these excursions. Some excursions occur quickly with no distinctive pre- or post-excursion anomalous directional variability. Other excursions are preceded by 10–20 ky of anomalous directional variability (high angular dispersion). Some also show continuing anomalous directions for 10–20 ky after the excursions. All of these features suggest a close relationship between excursions themselves and the surrounding PSV. Statistical studies of the PSV also show distinctive patterns to the PSV variability. The angular dispersion in 3-ky intervals shows a distinctive bimodal distribution with high (low) values associated with low (high) intensities. The high angular dispersion (and low intensity) are associated with the seven recorded excursions in these regions. There is reproducible evidence for another 5 excursions elsewhere in the world, but not in our records, that are also associated with high angular dispersion intervals. We think this is corroborative evidence for the reality of these excursions. That means that 12 excursions have occurred in the last 380 ka. Overall assessment of the PSV records suggests that important non-linear behavior occurs in the geodynamo as a function of intensity. This behavior is noted in the sharp changes between low/high angular dispersion intervals. It suggests that the 9-ky averaged field is more multipolar and far from axial dipole expectation during low paleointensity. Non-linearity is also seen in the fast polarity flips associated with the two Class II excursions.

Paleosecular variation record from Pleistocene-Holocene lava flows in southern Colombia

Improvements in the spatial and temporal coverage of paleomagnetic data are essential to better evaluate paleofield behaviour over the past 10 Myr, especially due to data scarcity at low latitudes in the South American region. Here, we provide new Pleistocene-Holocene (0–2 Ma age interval) paleodirectional data from three volcanic systems (Doña Juana Volcanic Complex, Galeras Volcanic Complex and Morasurco Volcano) in southwestern Colombia between latitudes 1.2 and 1.4°N. A total of 38 paleodirectional sites were studied using progressive alternating field and thermal demagnetization treatments. After excluding transitional data, we obtain thirty site-mean directions for analysis of paleosecular variation (PSV) and the time-averaged field (TAF) in the study area. The mean direction (Dec = 351.2°, Inc = −3.4°, α95 = 6.2°, k = 20.0) and the paleomagnetic pole (Plat = 80.7°N, Plon = 173.1°E, A95 = 5.2°, K = 29.1) of these sites are not statistically compatible with the expected geocentric axial dipole (GAD) field direction and geographic north pole, respectively. Virtual geomagnetic pole dispersion (SB) for our filtered dataset (SB(2Ma) = 15.212.017.6°) and the Brunhes chron (SB(Bru) = 16.011.619.1°) are consistent at the 95% confidence level with South American studies at equatorial latitudes and recent PSV models for the 0–10 Ma and Brunhes intervals. Likewise, the corresponding inclination anomaly (ΔI) for two age groups ΔI2Ma = − 5.9−12.10.3° and ΔIBru = − 5.3−13.73.1° suggests large deviations relative to the GAD model, in accordance with predictions from zonal TAF models. The high VGP dispersion could be linked to strong longitudinal variability of the magnetic equator position over South America. This feature reflects the presence of significant non-dipole field components in this region that have been detected in geomagnetic field models for the most recent centuries and millennia, probably associated with the presence of the South Atlantic Magnetic Anomaly in the South American region.