Geomagnetic Intensity Research Articles

Geomagnetic Field Intensity During the First Millennium BCE From Royal Judean Storage Jars: Constraining the Duration of the Levantine Iron Age Anomaly

AbstractThe rich and extensively studied archaeological record of the Near East provides an opportunity to develop a comprehensive archaeomagnetic dataset for exploring the behavior of the geomagnetic field with high precision. The Levantine archaeomagnetic curve (LAC) project is an ongoing effort to develop a continuous high‐resolution geomagnetic intensity curve for the Levant and Mesopotamia. The first version of the LAC covered the period between 3000 and 550 BCE. Here, we report archaeointensity data from 169 samples compiled into 32 groups dating between the 7th and the 1st centuries BCE aiming at extending the LAC up to the end of the first millennium BCE. Twenty‐two groups are assembled from storage jar handles bearing different types of royal seal impressions, which were used in Judah as part of a taxation administrative system. These groups are combined with 10 other groups of pottery assemblages, three of which are from Hellenistic destruction layers dated using radiocarbon and coins. The new curve shows that the Levantine Iron Age Anomaly (LIAA) spanned 550 years (1100 ‐ 550 BCE) and that the rate of decline during the last spike around 600 BCE could have reached ∼0.6 μT/year. During the 6th century, the virtual axial dipole moment (VADM) dropped from 160 ZAm2 to 125 ZAm2 after which field intensity only slightly increased to 135 ZAm2, until another considerable decline to ∼90 ZAm2 during the 3rd to the 1st centuries BCE. We highlight the archaeomagnetic implication of the new curve in inferring the relative chronological relationship between different stamp types.

Navigation by magnetic signatures in a realistic model of Earth's magnetic field.

Certain animal species use the Earth's magnetic field (i.e. magnetoreception) alongside their other sensory modalities to navigate long distances that include continents and oceans. It is hypothesized that several animals use geomagnetic parameters, such as field intensity and inclination, to recognize specific locations or regions, potentially enabling migration without a pre-surveyed map. However, it is unknown how animals use geomagnetic information to generate guidance commands, or where in the world this type of strategy would maximize an animal's fitness. While animal experiments have been invaluable in advancing this area, the phenomenon is difficult to studyin vivoorin situ, especially on the global scale where the spatial layout of the geomagnetic field is not constant. Alongside empirical animal experiments, mathematical modeling and simulation are complementary tools that can be used to investigate animal navigation on a global scale, providing insights that can be informative across a number of species. In this study, we present a model in which a simulated animal (i.e. agent) navigates via an algorithm which determines travel heading based on local and goal magnetic signatures (here, combinations of geomagnetic intensity and inclination) in a realistic model of Earth's magnetic field. By varying parameters of the navigation algorithm, different regions of the world can be made more or less reliable to navigate. We present a mathematical analysis of the system. Our results show that certain regions can be navigated effectively using this strategy when these parameters are properly tuned, while other regions may require more complex navigational strategies. In a real animal, parameters such as these could be tuned by evolution for successful navigation in the animal's natural range. These results could also help with developing engineered navigation systems that are less reliant on satellite-based methods.

A channel state information and geomagnetic fused fingerprint localisation algorithm based on multi‐input convolutional neural network

AbstractNumerous applications require indoor localisation, and one of the current research areas is how to leverage low‐cost ubiquitous signals for indoor localisation. This research designs a multi‐input convolutional neural network (Multi‐CNN) localisation approach to combine natural geomagnetic signals and universal 5G communication signals. To create the location fingerprint data, the geomagnetic three‐component data and channel state information (CSI) must first undergo independent preprocessing. Subsequently, the rebuilt CSI amplitude and geomagnetic intensity are employed for separate offline training to efficiently extract the corresponding data features. Lastly, Multi‐CNN is used to estimate the user's location online. The localisation outcomes for the conference room and hall demonstrate that the Multi‐CNN algorithm can achieve average localisation accuracies of 1.41 and 2.66 m, respectively. These are higher than the single‐input CNN algorithms by 21% and 15%, and higher than backpropagation network (BPNN) algorithm by 24% and 17%, and higher than the weighted K‐nearest neighbour algorithm by 34% and 28%. The Multi‐CNN‐based localisation approach successfully fuses the diverse data, potentially satisfying most indoor localisation applications.

Geomagnetic paleointensity dating of mid-ocean ridge basalts from the neo-volcanic zone of the Central Indian Ridge

Describing the evolution of the neo-volcanic zone in the spreading ridge is essential for understanding the dynamics and environments of abyssal basins. However, the absolute dating of ocean floor basalts is generally difficult. As a characteristic age indicator, absolute intensity of past geomagnetic field (absolute paleointensity, API) is useful to date ocean floor basalts. In this study, we adopted the Tsunakawa–Shaw method to measure APIs of whole-rock seafloor basalts collected from a conical cone on the Central Indian Ridge and performed rock magnetic experiments. We conducted the experiments on a total of 18 specimens (two or three specimens from each of eight lava sites). Six specimens from two lava sites with different morphologies (pillow and sheet), three for each, passed the acceptance criteria. API means at site level are 33.0 ± 1.0 and 35.8 ± 1.7 μT, respectively. The similarity of API site means suggests that they erupted within a short period. These site-level API means are approximately 0.7 to 0.8 times the present geomagnetic intensity of 46.0 μT at the sampling sites. The accepted specimens show higher Curie temperature, lower initial intensity of natural remanent magnetization, higher ratio of saturation remanence to saturation magnetization (Mrs/Ms), and signal of harder magnetic mineral than rejected ones. Our primary comparison between the two site-level API means and the 1590–present high-resolution IGRF-13 + gufm1 model constrains that the eruption timing of the conical cone to be < 1590 CE. When we compared the two site-level API means with the paleointensity curves calculated from the BIGMUDI4k.1 and ArchKalmag14 k.r, we found that they overlap in the period of − 7575 to −1675 CE or − 25 to 1590 CE, which may be the eruption timing of the conical cone. We concluded that timing of recent volcanic eruption in abyssal environment could be investigated by using appropriate rock magnetic selection and carefully examined API.Graphical

Exploring geomagnetic variations in ancient mesopotamia: Archaeomagnetic study of inscribed bricks from the 3rd-1st millennia BCE.

This study presents 32 high-resolution geomagnetic intensity data points from Mesopotamia, spanning the 3rd to the 1st millennia BCE. These data contribute to rectifying geographic disparities in the resolution of the global archaeointensity curve that have hampered our understanding of geomagnetic field dynamics and the viability of applying archaeomagnetism as a method of absolute dating of archaeological objects. A lack of precise and well-dated intensity data in the region has also limited our ability to identify short-term fluctuations in the geomagnetic field, such as the Levantine Iron Age geomagnetic Anomaly (LIAA), a period of high field intensity from ca. 1050 to 550 BCE. This phenomenon has hitherto not been well-demonstrated in Mesopotamia, contrary to predictions from regional geomagnetic models. To address these issues, this study presents precise archaeomagnetic results from 32 inscribed baked bricks, tightly dated to the reigns of 12 Mesopotamian kings through interpretation of their inscriptions. Results confirm the presence of the high field values of the LIAA in Mesopotamia during the first millennium BCE and drastically increase the resolution of the archaeointensity curve for the 3rd-1st millennia BCE. This research establishes a baseline for the use of archaeomagnetic analysis as an absolute dating technique for archaeological materials from Mesopotamia.

Possible evidence for geomagnetic intensity anomaly around 5500 BP from archaeomagnetic analyses of San Jacinto pottery, Caribbean Colombia

San Jacinto archaeological site in Northern Colombia hosts America's oldest pottery, radiometrically dated between 5940 ± 60 BP and 5190 ± 40 BP. Eleven ceramic fragments were subjected to detailed archaeomagnetic and archaeointensity investigation. Alternating field and thermal demagnetization, as well as magnetic mineralogy experiments, were carried out before double heating paleointensity determination to select the most suitable samples. Magnetic susceptibility vs. temperature curves revealed that magnetite and hematite grains are the main carriers of the thermoremanent magnetization. However, the contribution of hematite in total remanence seems to be negligible. Thirty-six samples corresponding to six pottery fragments were selected for Thellier-type paleointensity determinations. Mean intensity values range from 50.7 ± 4.7 to 65.3 ± 11.9 μT while virtual Axial Dipole Moments vary from 12.6 ± 1.2 to 16.2 ± 2.9 × 1022 Am2, indicating high geomagnetic field strength compared to values predicted by global geomagnetic models. This represents the first evidence of relatively high archaeointesities before 1000 BC. Similar or even higher geomagnetic strengths are observed in the Levant around 1100–800 BC and SW Pacific Region at 1450 AD. The actual cause of such anomalously high intensity, often attributed to the processes in the vicinity of the Core-Mantle Boundary, is still not fully understood.

Intelligent Geomagnetic Indoor Positioning System

In the past, several firefighters have died in disaster relief operations. Although the firefighters were fully equipped, the scene of the disaster was smoky and disorienting, making the firefighters unable to identify their location. The commander wanted to direct the firefighters outside but could not confirm the correct location of the firefighters, causing delays in rescue. GPS cannot support indoor positioning or preset indoor positioning facilities at the moment of fire extinguishing. However, geomagnetism is everywhere, and it can be used to identify one’s location. Unfortunately, due to the uncertainty of the magnetic field strength, indoor geomagnetism is affected by the building environment, and the existing magnetic positioning methods have difficulty obtaining a location. To solve this problem, we propose a new incremental indoor localization scheme based on the difference in geomagnetic intensity. The proposed method achieves indoor localization in 2D environments successfully. The novelty of our geomagnetic indoor positioning system is that it can perform indoor positioning without adding any indoor positioning facilities, and the accuracy can reach 0.8~1.5 m. This article aims to verify that the geomagnetic turbulence filtering algorithm can filter out abnormal geomagnetic intensity, that the incremental algorithm can estimate the position of human motion, and that geomagnetism can be used for indoor positioning without any preset infrastructure. The contribution of this paper is that we have developed a practical system that can be used without any infrastructure and can be used for indoor positioning with meter-level accuracy. The geomagnetic indoor positioning system can be integrated with a wireless network and applied to disaster relief.

Significance of Short‐Wavelength Magnetic Anomaly Low Along the East Pacific Rise Axis, 9°50′N

AbstractMagnetic anomaly variations near mid‐ocean ridge spreading centers are sensitive to a variety of crustal accretionary processes as well as geomagnetic field variations when the crust forms. We collected near‐bottom vector magnetic anomaly data during a series of 21 autonomous underwater vehicle Sentry dives near 9°50′N on the East Pacific Rise (EPR) covering ∼26 km along‐axis. These data document the 2–3 km wide axial anomaly high that is commonly observed at fast‐spreading ridges but also reveal the presence of a superimposed ∼800 m full wavelength anomaly low. The anomaly low is continuous for ≥13 km along axis and may extend over the entire survey region. A more detailed survey of hydrothermal vents near 9°50.3′N reveals ∼100 m diameter magnetic lows, which are misaligned relative to active vents and therefore cannot explain the continuous axial low. The axial magnetization low persists in magnetic inversions with variable extrusive source thickness, indicating that to the extent to which layer 2A constitutes the sole magnetic source, variations in its thickness alone cannot account for the axial low. Lava accumulation models illustrate that high geomagnetic intensity over the past ∼2.5 kyr, and decreasing intensity over the past ∼900 years, are both consistent with the broad axial anomaly high and the superimposed shorter wavelength low. The continuity of this axial low, and similar features elsewhere on the EPR suggests, that either crustal accretionary processes responsible for this anomaly are common among fast‐spread ridges, or that the observed magnetization low may partially reflect global geomagnetic intensity fluctuations.

Evolution of the Earth's magnetic field strength in northwestern Argentina during the last two millennia: Towards the improvement of south American geomagnetic paleosecular variation curve

A magnetic mineralogy and absolute geomagnetic intensity study was carried out on prehispanic ceramic fragments from the Southern Andes region (Northwest Argentina). Magnetic susceptibility vs. temperature curves and alternating field demagnetization treatments were applied to select the most suitable samples for the absolute archaeointensity experiments. A total of 66 samples were analyzed following the Thellier modified by Coe protocol, including cooling rate corrections and potential mitigation of the magnetic anisotropy effect. Thirty-eight samples (out of 66) belonging to nine pottery fragments yielded reliable absolute intensity determinations The new data, accompanied by associated radiocarbon ages, were integrated into previously published data in order to construct an improved paleosecular variation curve for South America. The highest quality data covers only the last 1000 years. The general variation patterns show good agreement with global geomagnetic prediction models. This updated regional curve may be used as the reference curve for archaeomagnetic dating in the major part of South America (Brazil, Argentina, Chile, Uruguay and Bolivia), even though caution should be paid for the areas and time periods poorly covered by data.

Quaternary Magnetic Stratigraphy of Deep‐Sea Sediments in the Western North Pacific: Influences of Paleomagnetic Recording Efficiency and Lock‐In Delay

AbstractUnderstanding past environmental changes in the western North Pacific is rather limited due to the general paucity of robust chronology for carbonate‐lacking pelagic clay sediments. Here, we present a new magnetostratigraphy of Quaternary deep‐sea sediments in the northern Mariana Basin. A comprehensive set of paleomagnetic, rock magnetic, and microscopic results reveal that paleomagnetic signals are mainly carried by detrital magnetic minerals of Asian eolian dust and volcanic origins. The volcanic materials, most likely from the Mariana Arc, are characterized by low coercivity (∼30 mT) interacting single domain (SD) and pseudo‐SD grains, associated with abundant dendritic magnetic crystals/inclusions. This volcanic component is a suitable remanence carrier but is less efficient in recording geomagnetic intensity than the higher coercivity eolian component. The relative paleointensity record derived with minimum rock magnetic artifacts shows comparable patterns with global templates. At the Matuyama‐Brunhes transition, a ∼2‐cm remanence lock‐in depth offset is identified from beryllium isotope records, and the estimated magnetostratigraphic age delay is small (∼8 kyr). Our results provide an improved understanding of remanence recording processes in carbonate‐poor deep‐sea clays and demonstrate magnetic stratigraphy as a valuable chronology in the western North Pacific region.

Archaeointensity record of weak field recurrence in Japan: new data from Late Yayoi and Kofun ceramic artifacts

Summary We present new absolute archaeointensity data from six archaeological sites situated in the Okayama Prefecture, Japan. The materials studied are well-dated fragments from pottery, ceramic coffins and haniwa artifacts. Their ages range from 160 AD to 675 AD, covering the Late Yayoi and Kofun periods. Rock magnetic experiments suggest the presence of magnetite and/or Ti-magnetite as the main carrier of the remanence, with a possible minor contribution of higher coercivity minerals. After thermal demagnetization experiments, the most magnetically stable samples were selected for archaeointensity analysis performed following the double-heating method proposed by Thellier and modified by Coe. Partial thermoremanent magnetization (pTRM) checks and pTRM tail-checks were performed for monitoring possible chemical alterations during heating. All measurements were corrected for both anisotropy and cooling-rate effects. Successful archaeointensity determinations, following rigorous selection criteria, were obtained for samples from all the investigated archaeological sites. Compared with literature data from Japan, the new high-quality data show significantly lower intensity values. They also reveal possible fast secular variation changes during the Late Yayoi period and very weak geomagnetic intensity field around 630 AD. Such values offer evidence of a possible recurrence of weak intensity field in East Asia, suggesting an ancient recurrence of the West Pacific Anomaly. The new data might change the archaeomagnetic field models interpretations in the area, even though more data are still necessary to better understand the secular variation in Japan and the temporal evolution of the geomagnetic field's behavior in East Asia.

The Cretaceous Normal Superchron: A Mini-Review of Its Discovery, Short Reversal Events, Paleointensity, Paleosecular Variations, Paleoenvironment, Volcanism, and Mechanism

The Cretaceous Normal Superchron (CNS) was first defined in the 1960s to explain the Cretaceous Quiet Zone in marine magnetic anomaly profiles, which includes no or fewer geomagnetic reversals. This ∼37 million years period is considered the most unique and extreme geomagnetic feature for the last 160 Myr. Superchrons may be caused by the geodynamo operating at peak efficiency with a unique heat flux at the core-mantle boundary (CMB). Previous studies suggest that the CNS is a sign of the connection between Earth’s interior and surface. During the CNS, the geomagnetic intensity may have fluctuated significantly, and the average may have changed with time, and the paleosecular variations had unique features. The warm climate around the CNS may have been caused by volcanic activity associated with active mantle convection. Such mantle convection increases heat flux at the CMB during the CNS, but geodynamo simulations predict small heat flux, which are inconsistent. This discrepancy may be resolved by the growth and collapse of a superplume or by an increase and decrease in the subduction flux.

Position Correction and Trajectory Optimization of Underwater Long-Distance Navigation Inspired by Sea Turtle Migration

Accumulating evidence suggests that migrating animals store navigational “maps” in their brains, decoding location information from geomagnetic information based on their perception of the magnetic field. Inspired by this phenomenon, a novel geomagnetic inversion navigation framework was proposed to address the error constraint of a long-distance inertial navigation system. In the first part of the framework, the current paper proposed a geomagnetic bi-coordinate inversion localization approach which enables an autonomous underwater vehicle (AUV) to estimate its current position from geomagnetic information like migrating animals. This paper suggests that the combination of geomagnetic total intensity (F) and geomagnetic inclination (I) can determine a unique geographical location, and that there is a non-unique mapping relationship between the geomagnetic parameters and the geographical coordination (longitude and latitude). Then the cumulative error of the inertial navigation system is corrected, according to the roughly estimated position information. In the second part of the framework, a cantilever beam model is proposed to realize the optimal correction of the INS historical trajectory. Finally, the correctness of the geomagnetic bi-coordinate inversion localization model we proposed was verified by outdoor physical experiments. In addition, we also completed a geomagnetic/inertial navigation integrated long-distance semi-physical test based on the real navigation information of the AUV. The results show that the geomagnetic inversion navigation framework proposed in this paper can constrain long-distance inertial navigation errors and improve the navigation accuracy by 73.28% compared with the pure inertial navigation mode. This implies that the geomagnetic inversion localization will play a key role in long-distance AUV navigation correction.

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IDENTIFICATION OF ROCK LAYER CONTACTS IN THE SURROUNDING OF THE SUTAMI DAM USING GEOMAGNETIC METHODS

Research on rock layer contact at Sutami Dam, Karangkates Village, Sumberpucung District, Malang Regency, Indonesia was undertaken. This research was conducted to identify volcanic sediments layers' which contact with Limestone Sediments in the surrounding of Sutami Dam and to mitigate potential disasters in the dam's surrounding area. This research was conducted by a geomagnetic method. Data were collected using the Proton Precession Magnetometer G-856. The geomagnetic data acquisition started from the Kromengan District (112.494oE; 8.129oS) to the Sukorame District (112.358oE; 8.213oS). The radius of geomagnetic data acquisition was 15 km; the space between the points was 300 meters with 1372 measurement points. The value of the geomagnetic intensity ​​are between -210 nT to 514 nT. The northern part of the research location has a lower total geomagnetic intensity than the southern area. The northern part is thought to be volcanic sediment (Tuff Desposits and Butak Volcanic Sediments), which only covers the surface, while the southern part is (Limestone Sediments) Marine sediment, which is some parts thought to have been volcanoes in ancient times. The ancient volcanoes in the southern part are Mounts Golo, Selorejo, Selumban, Tretes, Soko, Pehlembun and Krowedul. The contact layer between volcanic sediments with Limestone Sediments is more difficult to consolidate, so that the buildings built on them are more vulnerable.

The existence of underground gas storage causes geomagnetic anomaly in this area?

When the stress state of the rock changes, its permeability will also change accordingly, which is the so-called piezomagnetic effect. The piezomagnetic characteristics of rocks are an important and reliable physical basis for the seismomagnetic effect. Based on the experiments of rock magnetism, many scholars have carried out targeted experiments on the relationship between stress and rock magnetism, and achieved many important experimental understandings. As the largest underground gas storage (UGS) in operation in China, the Hutubi UGS has a design storage capacity of 10 billion cubic meters. It is operated periodically every year by gas injecting in summer and gas extracting in winter. During the process of gas injection and gas extraction in Hutubi UGS, the gas well pressure changes up to more than 10 MPa. Periodic injection and extraction operations will induce variations in the in-situ stress field in local areas. Whether these variations can cause local crustal magnetic anomalies is the focus of this paper. An observation network composed of 63 total geomagnetic intensity measuring stations was established in the Hutubi UGS and its surrounding areas, and the geomagnetic anomalies have been systematically observed. Based on the two phases of field observation data in October 2016 and October 2018, a polynomial fitting method was used to obtain the crustal magnetic anomalies in the UGS area. Results show that the existence of the Hutubi UGS has indeed caused the geomagnetic anomaly changes in this areas, the maximum value of the magnetic anomaly is 19 nT. The results of this field observation further confirmed the existence of the piezomagnetic effect in the laboratory and established the internal connection between the meso-scale crustal magnetic anomalies and the underground stress variations.

Fusion of wildlife tracking and satellite geomagnetic data for the study of animal migration

BackgroundMigratory animals use information from the Earth’s magnetic field on their journeys. Geomagnetic navigation has been observed across many taxa, but how animals use geomagnetic information to find their way is still relatively unknown. Most migration studies use a static representation of geomagnetic field and do not consider its temporal variation. However, short-term temporal perturbations may affect how animals respond - to understand this phenomenon, we need to obtain fine resolution accurate geomagnetic measurements at the location and time of the animal. Satellite geomagnetic measurements provide a potential to create such accurate measurements, yet have not been used yet for exploration of animal migration.MethodsWe develop a new tool for data fusion of satellite geomagnetic data (from the European Space Agency’s Swarm constellation) with animal tracking data using a spatio-temporal interpolation approach. We assess accuracy of the fusion through a comparison with calibrated terrestrial measurements from the International Real-time Magnetic Observatory Network (INTERMAGNET). We fit a generalized linear model (GLM) to assess how the absolute error of annotated geomagnetic intensity varies with interpolation parameters and with the local geomagnetic disturbance.ResultsWe find that the average absolute error of intensity is − 21.6 nT (95% CI [− 22.26555, − 20.96664]), which is at the lower range of the intensity that animals can sense. The main predictor of error is the level of geomagnetic disturbance, given by the Kp index (indicating the presence of a geomagnetic storm). Since storm level disturbances are rare, this means that our tool is suitable for studies of animal geomagnetic navigation. Caution should be taken with data obtained during geomagnetically disturbed days due to rapid and localised changes of the field which may not be adequately captured.ConclusionsBy using our new tool, ecologists will be able to, for the first time, access accurate real-time satellite geomagnetic data at the location and time of each tracked animal, without having to start new tracking studies with specialised magnetic sensors. This opens a new and exciting possibility for large multi-species studies that will search for general migratory responses to geomagnetic cues. The tool therefore has a potential to uncover new knowledge about geomagnetic navigation and help resolve long-standing debates.

Geomagnetic Field Paleointensity Spanning the Past 11 Myr From Marine Magnetic Anomalies in the Southern Hemisphere

AbstractGlobal variations in geomagnetic intensity can provide dating markers for sedimentary records, which is particularly helpful in precisely reconstructing climate changes. However, there are few continuous relative paleointensity (RPI) records derived from sediments spanning the past 11 Myr, and those that exist generally bear a high degree of uncertainty. Therefore, independent evidence from other continuous paleointensity records is needed to verify the existing information. Here, we analyzed magnetic anomaly profiles from the East Pacific Rise and the Southeast Indian Ridge and discovered correlative tiny wiggles in the stacked profiles from three different areas. A comparison with a previous magnetic study on the South Atlantic Ridge and the synthetic profile from RPI records generated for the past ∼8 Myr confirmed that the small wavelength anomalies result from global geomagnetic intensity fluctuations. The newly calibrated timescales from selected marine magnetic anomalies could provide a potential dating reference for sedimentary strata.

Refining geomagnetic field intensity changes in Europe between 200 CE and 1800 CE. New data from the Mediterranean region

Absolute past geomagnetic intensity values can mainly be recovered by fired archaeological materials and volcanic rocks. Here, we present 10 new archeointensities from the Mediterranean region that help to better constrain geomagnetic field intensity changes in Europe over the last two millennia. The new archeointensity results were obtained from the Thellier classical method including thermoremanent magnetization (pTRM) checks and both the TRM anisotropy and cooling rate corrections and were derived from at least three specimens. The new data presented, together with a selection of previous archeointensities satisfying a set of quality criteria, confirm the presence of several intensity maxima in Europe over the last 2000 years. In particular, the new archeointensities allow to better define the starting point of the double-oscillation feature that occurred in Europe during the second half of the first millennium CE, and reinforce the existence of a relative maximum at the end of the 14th century - beginning of the 15th century in Western Europe. From selected European archeointensities two new paleosecular variation curves are constructed for Western and Eastern Europe using temporal cubic b-splines in a bootstrap approach. The obtained curves suggest that the occurrence of the intensity maxima is characterized by a period of about 300 ± 50 years. In addition, our results suggest that the maxima do not occur simultaneously in Western and Eastern Europe, pointing out an intensity eastward drift with a mean lag-time of about 100 years.

Equatorial auroral records reveal dynamics of the paleo-West Pacific geomagnetic anomaly

Localized regions of low geomagnetic intensity such as the South Atlantic Anomaly allow energetic particles from the Van Allen radiation belt to precipitate into the atmosphere and have been linked to a signature in the form of red aurora-like airglow visible to the naked eye. Smoothed global geomagnetic models predict a low-intensity West Pacific Anomaly (WPA) during the sixteenth to nineteenth centuries characterized by a simple time dependence. Here, we link the WPA to an independent database of equatorial aurorae recorded in Seoul, South Korea. These records show a complex fluctuating behavior in auroral frequency, whose overall trend from 1500 to 1800 AD is consistent with the locally weak geomagnetic field of the WPA, with a minimum at 1650 AD. We propose that the fluctuations in auroral frequency are caused by corresponding and hitherto unknown fluctuations in the regional magnetic intensity with peaks at 1590 and 1720 AD, a time dependence that has been masked by the smoothing inherent in regularized global geomagnetic models. A physical core flow model demonstrates that such behavior requires localized time-dependent upwelling flows in the Earth's core, possibly driven by regional lower-mantle anomalies.