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In recent years, it has been found that magnetic dip caused by diamagnetic motion of injected plasma can provide an appropriate environment for excitation of electromagnetic ion cyclotron (EMIC) waves. These findings have been widely reported in the Earth's magnetic environment. However, it has rarely been reported in Jupiter's magnetic environment. This paper reports the characteristics of EMIC waves observed by Juno in the magnetic dip of Jupiter. Multiple‐band EMIC waves are observed in frequency range from 10−3 Hz to several Hz. The theoretical analysis shows that in this event both He+ band and O+ band EMIC waves can be constrained in the magnetic dip, which is consistent with the wave emissions observed inside the magnetic dip. Our result provides the first evidence that EMIC wave can be ducted inside a magnetic dip in Jupiter's magnetosphere. Plain Language Summary: The relationship between magnetic structures and electromagnetic waves in the Earth's magnetosphere has been widely reported. Recent studies have theoretically displayed the effects of the magnetic dip on the EMIC wave propagation in Earth's magnetic field. In this paper, we use the event observed by Juno in the magnetic environment of Jupiter to analyze the effect of the magnetic dip on the propagation of EMIC waves. As a result, the observed EMIC waves can be ducted inside the magnetic dip of Jupiter's magnetosphere. Since these ducted waves would influence the dynamics of energetic protons through longtime scattering effects, the magnetic dip is expected to play an important role in the dynamics of Jupiter's magnetosphere. Key Points: Electromagnetic ion cyclotron (EMIC) waves are observed during the magnetic dip by JunoTheoretical analysis about the effects of magnetic dips on the EMIC wave propagation in Jupiter's magnetosphere is performedBoth He+ and O+ band EMIC waves can be ducted inside the magnetic dip in Jupiter's magnetosphere [ABSTRACT FROM AUTHOR]

How and when sedimentary rocks record Earth's magnetic field is complex. Most studies assume a time‐progressive lock‐in mechanism during sediment deposition called depositional remanent magnetization (DRM). However, magnetic minerals can also form in situ, recording a chemical remanent magnetization (CRM) that is discontinuous in time. Disentangling the two mechanisms represents a major hurdle, and differences in their recording efficiencies remain unexplored. Here, our theoretical solutions demonstrate that CRM intensities exceed DRM by a factor of six when acquired in the same magnetic field. Novel experiments growing greigite (Fe3S4) in sediments and subsequent redeposition under identical magnetic field conditions confirm the predicted difference in recording efficiency. Thus, if left unrecognized, CRM leads to overestimated paleointensity and deserves more attention when interpreting Earth's magnetic history from sedimentary records. Recognition of fundamental differences between CRM and DRM characteristics provide a way forward to distinguish the recording mechanisms through routine laboratory protocols. Plain Language Summary: Remanent magnetizations preserved in sedimentary rocks serve as a continuous record of Earth's magnetic field history and play a fundamental role in understanding the Earth system. It is commonly assumed that magnetic minerals align with the magnetic field as a particle settles through the water column, known as a depositional remanent magnetization (DRM). However, diagenesis can lead to chemical growth of magnetic minerals, known as a chemical remanent magnetization (CRM). CRM lacks stratigraphic continuity and can obscure or completely overprint the original magnetization any time after sediment deposition, leading to a magnetic record that is uncorrelated with the age of the rock. Yet, CRMs go largely unrecognized. Theory and experiments in our paper document that CRMs record the magnetic field six times more efficiently than DRMs. Our work provides a way to distinguish the two through routine laboratory protocols. Key Points: Recording efficiency of chemical remanent magnetization (CRM) is six times higher than depositional remanent magnetization (DRM)Undetected chemical remanences lead to overestimated relative paleointensity estimatesComparison of natural and laboratory magnetization and demagnetization behavior help identify chemical remanent magnetizations in sediments [ABSTRACT FROM AUTHOR]

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth's thermosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N2 and neutral temperature (at ∼160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe a heretofore unseen spatial morphology simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator‐to‐pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K. Plain Language Summary: On Saturday 10 May 2024, the sun launched a wave of energized plasma toward the Earth. A large disturbance in the Earth's magnetic field associated with the solar wind resulted in an extreme geomagnetic storm. The storm impacted power grids, disrupted navigational systems used by farming equipment, and produced aurora seen around the globe. The storm produced remarkable effects in the Earth's upper atmosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission. In this letter, we use images measured by GOLD to directly link atmospheric dynamics resulting from the May 10–12 superstorm with dramatic changes in composition, temperature, and global circulation in the Earth's upper atmosphere. We observe previously unseen structure in the upper atmosphere associated with equator‐to‐pole temperature differences exceeding 400 K. Peak neutral temperatures near 160 km exceed 1400 K at high latitudes. Key Points: GOLD disk images of ΣO/N2 and neutral temperature link storm time dynamics with changes in thermospheric composition and temperatureWe observe a previously unseen spatial morphology in ΣO/N2, neutral temperature, and total electron contentPeak equator‐to‐pole temperature differences exceed 400 K but relax to pre‐storm conditions well before ΣO/N2 [ABSTRACT FROM AUTHOR]

Earth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm. Plain Language Summary: The layer of Earth's atmosphere above 100 km is referred to as the "thermosphere" and can be thought of as the boundary between the space environment above it and the atmosphere below it. In early May 2024, an active sunspot ejected a significant amount of charged particles (protons and electrons) within a strong magnetic field toward Earth. This "coronal mass ejection" or CME encountered Earth's high atmosphere 10–13 May, causing a significant "geomagnetic storm" that significantly heated the thermosphere and modified its chemical composition. The effects of this storm were observed by the SABER instrument which is flying on the NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observes infrared light emitted by carbon dioxide, nitric oxide, molecular oxygen, and ionized nitric oxide produced during the storm. The 10–13 May storm caused the global average infrared radiation levels to increase by nearly a factor of 10 at some wavelengths in 1 day. The storm and the infrared radiation levels dissipated back to pre‐storm levels over the next 2 days. This storm was the third strongest in terms the power (2.64 trillion watts) radiated by the thermosphere in the past 22 years observed by SABER. The observed enhancements in infrared radiation at multiple wavelengths offer the opportunity to more fully understand how the Sun interacts with and influences Earth's highest atmosphere. Key Points: The daily Ap (273 nT) and Dst (−291.94 nT) indexes on 11 May 2024 were the largest since the launch of the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite in December 2001The power radiated 11 May by NO and CO2 exceeded 1 TW each and the NO power (1.41 TW) exceeded the CO2 power (1.35 TW) for the first timeTotal storm radiated power, above background, is 2.64 TW (2.28 × 1017 J), making it the third strongest storm during the TIMED era [ABSTRACT FROM AUTHOR]

Twenty‐two years (2002–2023) of infrared radiative cooling rate data derived from the SABER instrument on the NASA TIMED satellite are presented. Global daily and global annual infrared power (Watts, W) emitted by nitric oxide (NO) and carbon dioxide (CO2) illustrate the variability of the geospace environment on timescales from days to decades. The 11‐year solar cycle (SC) is evident in the global power data and in vertical profiles of infrared cooling rates (nW/m3). The global annual power radiated by NO and CO2 are larger in 2023 than at any time since 2003 and 2002, respectively. The to‐date peak in NO infrared power in SC 25 is larger than in SC 24, is comparable to SC 20, but is less than in SCs 18–19 and 21–23. Two geomagnetic storms in 2023 radiated more than 1 TW and are in the top 10 strongest storms observed by SABER. Plain Language Summary: SABER is an instrument on the NASA TIMED satellite, launched in December 2001, and is still operating nominally in 2024. SABER measures the amount of infrared energy emitted by the nitric oxide (NO) molecule and the carbon dioxide (CO2) molecule from Earth's thermosphere, the region of atmosphere above 100 km altitude. These measurements are used to derive the amount of power (Watts) radiated globally by these two molecules on daily to annual timescales. The infrared power data is then analyzed to determine its variability in the lower thermosphere from daily to decadal time scales. Of particular interest is the influence of the well‐known 11‐year cycle of solar activity which is readily evident in the infrared power data. SABER also observes the effects of geomagnetic storms, identifying two strong storms in 2023 that each produced over 1 TW of infrared power. Key Points: SABER on TIMED has observed infrared radiation from the thermosphere since January 2002, for 22 years, the equivalent of two solar cyclesGlobal annual infrared power radiated by NO and CO2 are larger in 2023 than any time since 2003 and 2002, respectivelyTwo geomagnetic storms in 2023 exceeded 1 TW of radiated energy, above background, and are in the top 10 strongest storms observed [ABSTRACT FROM AUTHOR]

On 24 April 2023, a Coronal Mass Ejection event caused the solar wind to become sub‐Alfvénic, leading to the development of an Alfvén Wing configuration in the Earth's magnetosphere. Alfvén Wings have previously been observed as cavities of low flow around moons in Jupiter's and Saturn's magnetospheres, but the observing spacecraft did not have the ability to directly measure the Alfvén Wings' current structures. Through in situ measurements made by the Magnetospheric Multiscale spacecraft, the 24 April event provides us with the first direct measurements of current structures during an Alfvén Wing configuration. These structures are observed to be significantly more anti‐field‐aligned and electron‐driven than the typical diamagnetic magnetopause current, indicating the disruption caused to the magnetosphere current system by the Alfvén Wing formation. The magnetopause current is then observed to recover more of its typical, perpendicular structure during the magnetosphere's recovery from the Alfvén Wing formation. Plain Language Summary: The solar wind applies pressure on the Earth's magnetic field, distorting it from a dipole into its compressed dayside and stretched tail configuration. However, this typical structure can be disrupted by eruptive solar events such as Coronal Mass Ejections (CMEs), which may cause the solar wind's pressure to drop low enough that it is no longer able to push the magnetosphere back to form a single unified tail. When this occurs, the tail splits into two separate structures, called Alfvén Wings. While this configuration is rare at Earth, it is common from interactions of the outer planets' magnetosphere's with their moons, where Alfvén Wing configurations have been studied and modeled. However, because the observing spacecraft lacked the necessary instrumentation, we have not yet directly observed the Alfvén Wing current structures. On 24 April 2023, a CME event led to the creation of an Alfvén Wing formation in the Earth's magnetosphere. We observed this event using the Magnetospheric Multiscale spacecraft, which enabled us to make the first direct observations of Alfvén Wing current structures. These currents were found to be mainly parallel to the local magnetic field, in contrast to typical magnetopause currents. Key Points: On 24 April 2023, the Magnetospheric Multiscale (MMS) spacecraft observed an Alfvén Wing formation along the dawn‐flank of Earth's magnetosphereMMS's observations represent the first in situ measurements of Alfvén Wing current structuresThe current structures are found to be primarily anti‐field‐aligned, electron‐driven, and filamentary [ABSTRACT FROM AUTHOR]

Surface atmospheric electric field (AEF) measurements were conducted using a Kelvin water dropper equalizer by the Japan Meteorological Agency's geomagnetic observatory at Kakioka, Ibaraki Prefecture, Japan, from 1929 to February 28, 2021. To obtain AEF data successive to the water dropper measurement, we independently installed the field mills at Kakioka. In this present study, we estimated the calibration coefficients based on comparisons between the water dropper and the field mills through parallel observations over 3 days. The results revealed that the new observations could be regarded as continuous data. Our new data from the field mills in this study have begun the process of being distributed in GLObal Coordination of Atmospheric Electricity Measurements (GloCAEM) as both archived and real‐time data in 1 min and 1 s samplings. [ABSTRACT FROM AUTHOR]

Paleomagnetic data is collected from bulk samples, containing a mixture of stable and unstable magnetic particles. Recently, magnetic microscopy techniques have allowed the examination of individual magnetic grains. However, accurately determining the magnetic moments of these grains is difficult and time‐consuming due to the inherent ambiguity of the data and the large number of grains in each image. Here we introduce a fast and semi‐automated algorithm that estimates the position and magnetization of dipolar sources solely based on the magnetic microscopy data. The algorithm follows a three‐step process: (a) employ image processing techniques to identify and isolate data windows for each magnetic source; (b) use Euler Deconvolution to estimate the position of each source; (c) solve a linear inverse problem to estimate the dipole moment of each source. To validate the algorithm, we conducted synthetic data tests, including varying particle concentrations and non‐dipolarity. The tests show that our method is able to accurately recover the position and dipole moment of particles that are at least 15 μm apart for a source‐sensor separation of 5 μm. For grain concentrations of 6,250 grains/mm3, our method is able to detect over 60% of the particles present in the data. We applied the method to real data of a speleothem sample, where it accurately retrieved the expected directions induced in the sample. The semi‐automated nature of our algorithm, combined with its low processing cost and ability to determine the magnetic moments of numerous particles, represents a significant advancement in facilitating paleomagnetic applications of magnetic microscopy. Plain Language Summary: Very small magnetic particles in rocks and other materials can store information about what the Earth's magnetic field was like in the past. But not all particles are good recorders of this magnetic information, and some may have recorded different overlapping directions and strengths. So it is important to measure each particle separately in order to identify and separate the good recorders from the bad ones. A device called a "quantum diamond microscope" is able to measure the magnetic field near the surface of a rock sample at microscopic scale. We propose a new method for processing data from this microscope that is able to find out the individual magnetizations of large amounts of small magnetic particles automatically. We created a computer program to execute the method, which calculates the 3D position and magnetization of each particle using the simple model of a magnetic dipole. We tested the method on simulated data, using fake magnetic particles for which we know the correct magnetization and position, and real data, both of which showed good results in most cases. The method we created has the potential to enable the widespread study of the magnetism of natural materials with more detail than before. Key Points: We present a fast algorithm to estimate the position and magnetization of individual sources using only magnetic microscopy dataThe algorithm was validated using synthetic samples that included both dipolar and non‐dipolar sources with varying depths and intensitiesThe successful application of the algorithm on a speleothem sample represents an advancement of this methodology for paleomagnetic studies [ABSTRACT FROM AUTHOR]

Volcanic rocks, preserving paleorecords of Earth's magnetic field, are essential to constrain the working of the geodynamo, provided their primary signal was not biased. Using a thermomagnetometer, we simulate a situation where a sample's primary record, carried by a thermoremanence (TRM, acquired by cooling in air from 600°C to room temperature), is partly overprinted by a chemical remanence (CRM, acquired by 200 hr of isothermal exposure at 400°C). This situation leads to two directional and intensity components (in the form of linear segments) in the Zijderveld and Arai‐Nagata diagrams. In the case of unstable titanomagnetite grains prior to CRM acquisition, we show that both components can be strongly biased by up to ∼50° for paleodirections and ∼50% for paleointensities. In such a worst‐case scenario, the secondary CRM strongly overprints the primary TRM, rendering the common interpretation of Zijderveld and Arai‐Nagata diagrams in terms of characteristic components invalid. Plain Language Summary: Volcanic rocks, the magnetic minerals of which can acquire a thermoremanent magnetization (TRM) from Earth's magnetic field during their initial cooling, are essential to constrain the working of the geodynamo through Earth's history. However, if the rock is subsequently reheated at moderate temperature in another ambient field, the initial record can be partly overprinted by a chemical remanence (CRM). Starting from a TRM applied on materials of various thermostability, we reproduced in laboratory conditions the acquisition of a CRM by annealing the rock in a controlled ambient field for 200 hr at 400°C. Rock‐magnetic and structural analyses at regular intervals, supplemented by continuous measurements of the remanent magnetization, indicate the creation of new phases as a result of oxidation processes. The paleomagnetic analysis of the final products reveals the existence of two distinct components that can be associated with the initial TRM and the secondary CRM. Whereas the paleomagnetic record of the initial TRM is trustworthy for the most stabilized initial products, directional (up to 50°) and intensity (up to 50%) biases are observed for the least stabilized initial products, illustrating a critical example where the interpretation of characteristic components (linear segments in the interpretation diagrams) is invalid. Key Points: We overprint a thermoremanent magnetization (TRM) by cooling from 600°C with a chemical remanent magnetization by 200 hr exposure at 400°CChemical remanent magnetization was produced by the creation of cation‐deficient titanomagnetite phases, then stabilized by oxyexsolutionPaleodirections and intensities are strongly biased in the worst scenario, making the interpretation of characteristic components invalid [ABSTRACT FROM AUTHOR]

Paleomagnetic results obtained from 38 Pliocene—Pleistocene volcanic flows from the Knot of the Pastos and surroundings of Puracé volcano and Popayán (southwestern Colombia) are presented. Using stringent quality criteria and excluding sites that classify as representatives of transitional states of Earth's field, a selected group of 27 sites (16 with normal polarity and 11 with reversed polarity) was obtained with a mean direction (Dec = 357.8°, Inc = 6.4°, α95 = 7.5° and κ = 15) that coincides with the geocentric axial dipole field (GAD: Dec = 0o, Inc = 3.2o) and, unlike similar studies at similar latitudes, does not coincide with the GAD plus a 5% axial quadrupolar component (Dec = 0°, Inc = −1.08°). However, when serial correlation (SC) among several sites with high inclination anomalies is taken into consideration, the mean direction of two resulting groups of sites shows greater consistency with a field that includes a quadrupolar component. It is interpreted that the sites treated for SC record states of the field similar to today's field in the area of study, which is being affected by the South Atlantic Anomaly. Plain Language Summary: The only way to study Earth's magnetic field in the geologic past from experimental data is by studying the magnetization of rocks that record Earth's field in a way comparable to the way compasses point close to the geographic north. Earth's magnetic field changes are significant in relatively short time‐scales like years or centuries. In this study the paleomagnetic directions recorded in volcanic products from extinct volcanoes of the Colombian Andes were obtained. Most of the volcanic flows record paleomagnetic directions consistent with the ones obtained from previous studies, which in general differ from the present magnetic directions in the area by being less inclined downwards. However, some of the volcanic flows did record paleomagnetic directions that are similar to the present magnetic directions in the area, which have been linked to an ample low magnetic intensity area in the Atlantic Ocean called the South Atlantic Anomaly. So, as it has been pointed out in other studies, it is possible that this anomaly has acted recurrently during the geologic past. Key Points: The mean paleomagnetic direction among the selected sites from Colombia shows consistency with a geocentric axial dipole (GAD) fieldConsistency with a GAD field with a 5% quadrupolar component is obtained when serial correlation is appliedSerially correlated sites are probably affected by the South Atlantic Anomaly, in a way similar to the present field in the study area [ABSTRACT FROM AUTHOR]

Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high‐quality directional data set, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation, compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84–23 Ma). The data set is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over‐lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G‐style quadratic fits and covariant Giant Gaussian Process models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth's long‐term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations. Plain Language Summary: The geomagnetic field is saved in volcanic rocks, which can be used to study the direction and intensity of this field millions of years later. The magnetic field is formed in the geodynamo in the Earth's outer core. The study of geomagnetic field changes through time gives us information on the changes in the Earth's outer core, lower mantle and inner core. In this study, all the data from the Paleogene and Late Cretaceous were gathered (84–23 million years ago) and studied to see how much the geomagnetic field changed through that time. With this study we now have information on the variability of the field for the entirety of the past 320 million years. We see that during the last 250 million years, the directional variability of the field seems to have varied little, even though the frequency of reversals varied massively. Some numerical simulations of the dynamo process occurring in Earth's core had previously suggested that both of these two things were directly correlated to the magnitude of heat flowing from the outer core to the mantle. Our new results suggest a more complex, nuanced picture. Key Points: A new data set, paleosecular variation of the Paleogene, comprising 1,667 paleomagnetic directions from 45 different localities of volcanics aged between 84 and 23 MaMedian equatorial dispersions of virtual geomagnetic poles have overlapping uncertainty bounds since 250 MaLarge fluctuations in the reversal frequency are not associated with large fluctuations in the inferred median axial dipole dominance [ABSTRACT FROM AUTHOR]

We present the observations of field‐aligned currents and the equatorial electrojet during the 23 March 2023 magnetic storm, focusing on the effect of the drastic decrease of the solar wind dynamic pressure occurred during the main phase. Our observations show that the negative pressure pulse had significant impact to the magnetosphere‐ionosphere system. It weakened large‐scale field‐aligned currents and paused the progression of the storm main phase for ∼3 hr. Due to the sudden decrease of the plasma convection after the negative pressure pulse, the low‐latitude ionosphere was over‐shielded and experienced a brief period of westward penetration electric field, which reversed the direction of the equatorial electrojet. The counter electrojet was observed both in space and on the ground. A transient, localized enhancement of downward field‐aligned current was observed near dawn, consistent with the mechanism for transmitting MHD disturbances from magnetosphere to the ionosphere after the negative pressure pulse. Plain Language Summary: The solar wind is a continuous stream of charged particles blowing from the Sun. The Earth's magnetic field forms a protective shield around our planet, called the magnetosphere, which deflects most of the solar wind particles away from the Earth. Disturbances in the solar wind can interact with the magnetosphere and impact the Earth's upper atmosphere (ionosphere). The interaction creates electric fields forcing charged particles to move in the magnetosphere, which creates electric currents flowing along the magnetic field lines connecting to the high‐latitude ionosphere and drives the movement of charged particles there. The low‐latitude ionosphere is generally shielded from these electric fields. Sudden changes in the solar wind can break such balance, leading to the electric field penetration to low latitudes. We examined how the magnetosphere and ionosphere interacted during the 23 March 2023 geomagnetic storm, focusing on what happened when the solar wind dynamic pressure suddenly decreased. We found the pressure drop caused a sudden decrease of the high‐latitude electric field, resulting in a brief period of overshielding and the electric field in the equatorial ionosphere reversed its direction. This changed the direction of the equatorial electrojet, a major electric current in the ionosphere at the magnetic equator. Key Points: Direct evidence of prompt penetration of electric field in the equatorial ionosphere caused by negative solar wind pressure pulseTransient counter electrojet caused by westward penetration electric field after the arrival of negative pressure pulseSignificant decrease of global large‐scale field‐aligned currents (FACs) and transient enhancement of localized FAC in response to negative pressure pulse [ABSTRACT FROM AUTHOR]

Volcanic rocks are considered reliable recorders of past changes in the Earth's magnetic field. Recent flows, however, sometimes fail to produce the known magnetic field at the time of cooling. Previous research on Mt. Etna suggests paleomagnetic data might not be accurately recorded. Here we test the accuracy of paleomagnetic data obtained from Mt. Etna lavas by comparing paleomagnetic data from historical flows to direct measurements of the magnetic field above the current topography. The inclinations and intensities in both data sets are biased toward lower values, while there is no such trend for the declination. Inclinations are on average 2.9° lower than expected; intensities are on average 8.8 µT lower. The deviations from the expected values depend on the height above the flow. Moreover, the inclinations and intensities vary as a function of topography. Both are higher above ridges and lower in gullies; the variations within a site are up to 14.1° in inclination and 12.9 µT for intensity. To suppress this paleomagnetic data bias it is important to take samples several meters apart and from different parts of the flow whenever possible. While this leads to a higher degree of scatter in paleodirections, the results better represent the Earth's magnetic field at the time of cooling. This emphasizes the importance of reporting paleomagnetic sampling strategies in detail. Plain Language Summary: Paleomagnetic data from lavas is routinely used in the Earth Sciences to for example, reconstruct the past behavior of the Earth's magnetic field, or make models of past plate motions. Very young flows for which the ambient magnetic field at the time of cooling is known, however, sometimes fail to produce the known reference values. Lava flows from Mt. Etna are extensively studied in the past and the paleomagnetic data obtained does often not agree with the known magnetic field value in which the lavas cooled. Here we show that the topography of volcanic terrain may influence the magnetic signal of new, overlying, flows, and we make recommendations for sampling strategies that suppress these terrain effects as much as possible. Key Points: Paleomagnetic data from Mt. Etna does often not reproduce the known geomagnetic field wellLocal magnetic anomalies explain bias in paleomagnetic data as function of topographyOptimizing the paleomagnetic sampling strategy may suppress this bias in paleomagnetic data [ABSTRACT FROM AUTHOR]

Joule heating is one of the main energy inputs into the thermosphere‐ionosphere system. Precise modeling of this process is essential for any space weather application. Existing thermosphere‐ionosphere models tend to underestimate the actual Joule heating rate quite significantly. The Thermosphere‐Ionosphere‐Electrodynamics General‐Circulation‐Model applies an empirical scaling factor of 1.5 for compensation. We calculate vertical profiles of Joule heating rates from approximately 2,220 hr of measurements with the EISCAT incoherent scatter radar and the corresponding model runs. We investigate model runs with the plasma convection driven by both the Heelis and the Weimer model. The required scaling of the Joule heating profiles is determined with respect to the Kp index, the Kan‐Lee merging electric field EKL, and the magnetic local time. Though the default scaling factor of 1.5 appears to be adequate on average, we find that the required scaling varies strongly with all three parameters ranging from 0.46 to ∼20 at geomagnetically disturbed and quiet times, respectively. Furthermore, the required scaling is significantly different in runs driven by the Heelis and Weimer model. Adjusting the scaling factor with respect to the Kp index, EKL, the magnetic local time, and the choice of convection model would reduce the difference between Joule heating rates calculated from measurement and model plasma parameters. Plain Language Summary: The vast majority of the energy input to the Earth system originates from the sun. This includes the absorption of various types of radiation, for example, ultraviolet radiation in the ozone layer or visible light and infrared radiation at the surface. In the upper atmosphere above about 80 km altitude, the absorption of extreme ultraviolet radiation and soft X‐rays plays a major role. However, other processes also contribute significantly to the heating of this region, for example, the energy dissipation in the form of electric currents flowing along electric fields, also known as Joule heating. Joule heating is highly variable and can be drastically enhanced especially during solar storms, which can have potentially disastrous effects on satellites. Accurate modeling, and therefore also prediction, of Joule heating is not possible at the moment since thermosphere‐ionosphere models have to scale the Joule heating empirically to fit the actual values. We investigate how the required scaling changes under different geophysical conditions. Key Points: The constant Joule heating scaling factor in TIE‐GCM is inadequate to compensate for the underestimation under various geomagnetic conditionsJoule heating rates calculated from 2,220 hr of EISCAT measurements are compared to TIE‐GCM runs driven with the Heelis and Weimer convection modelsThe required scaling factor varies significantly with the Kp index, the Kan‐Lee merging electric field, and the magnetic local time [ABSTRACT FROM AUTHOR]

Plain Language Summary: Nearly synchronous global changes in geomagnetic polarity give both a detailed irregular pacing to geological time and provide a glimpse into heat transfer processes across the core—mantle boundary which drives the Earth's geodynamo. Although the Late Carboniferous is characterized by some well‐studied reversals, details of the tempo of polarity changes in the Early Carboniferous are unknown. This work addresses this by providing a detailed record of polarity changes over a ∼2 million year interval at around 334.5–332.5 million years ago‐from the Trowbarrow Quarry section in NW England. We demonstrate that these limestones likely preserve magnetization from close to their time of formation and record at least 31 polarity reversals. These observations support the idea that the Earth's dynamo was in a hyperactive reversing state similar to those sustained for tens of Myr in the Late Jurassic, parts of the Cambrian and the Late Ediacaran. It further corroborates a ∼200 Myr cyclicity in paleomagnetic field behavior since the Precambrian, potentially linked to variable core heat flow forced by mantle convection. The pattern of geomagnetic polarity changes during the Early Carboniferous (Mississippian) is not known in detail. This information sparsity is addressed by determining a magnetostratigraphy from the late Asbian (late Visean at ∼333 Ma) in Trowbarrow Quarry, UK. This is the stratotype section of the late Asbian and has a detailed foraminiferal zonation based on the same set of paleomagnetic samples, establishing a detailed biostratigraphy. The 195 m‐thick section was sampled at an average spacing of 1.1 m, yielding a detailed magnetostratigraphy comprising nine major magnetozone couplets, and seven submagnetozones. The section dataset has a 78% bias to normal polarity determined from 177 sampling levels. The magnetization is carried by a mixture of hematite and detrital magnetite, with 68% of specimens dominated by hematite magnetizations. The primary magnetization passes a fold test showing its age was prior to the latest Carboniferous. The hematite is inferred to be largely of detrital, eolian origin, although some reddened levels are associated with emergent surfaces, suggesting that a small fraction of hematite is associated with platform emergence. The Mississippian age magnetization is partly overprinted with Kiaman Superchron‐age and Brunhes‐age magnetizations. Using the duration of the section based on astrochronology indicates a reversal frequency of 15.7 ± 0.75 Myr−1, indicating that the geodynamo was in a hyperactive reversing state between 335 and 333 Ma. Key Points: A 195 m section, representing ∼2 Myr, yields a magnetostratigraphy comprizing nine major magnetozone couplets and seven submagnetozonesPrimary magnetizations are predominantly carried by hematite with lesser important detrital magnetite. Data pass regional fold testsA reversal frequency of 15.7 ± 0.75 Myr−1 is calculated, suggesting that the geodynamo was in a hyperactive state at ∼333 Ma [ABSTRACT FROM AUTHOR]

High‐speed jets (HSJs) are commonly observed in the Earth's magnetosheath. The HSJs can drive shock‐like bow waves when compressing the ambient plasma, which are important for the HSJ's evolution and the energization of charged particles. Here we present the first two‐dimensional hybrid simulation of the formation and evolution of jet‐driven bow waves. The simulated bow waves exhibit localized enhanced magnetic field and ion density, with their peaks separated by the order of ion inertial length. The bow waves are formed when a super‐magnetosonic HSJ encounters a magnetic structure with the magnetic field nearly perpendicular to the HSJ's velocity. The magnetic field structure acts as an obstacle to deflect and decelerate the jet, causing the pile up of ions on the jet side and the compression of the magnetic structure on the downstream side. Our study explains the observed properties of bow waves, and helps to better understand the evolution of HSJs. Plain Language Summary: When the solar wind interacts with the Earth's magnetic field, it creates a bow shock in front of the magnetosphere. The bow shock slows down and heats up the solar wind plasma, creating a turbulent area known as the magnetosheath. Sometimes, high‐speed jets (HSJ), observed as high velocity and density pulses, are detected in the magnetosheath. The HSJs can transfer the solar wind plasma through the magnetosheath and potentially affect the near‐Earth space where satellites orbit. Recent studies have found that the HSJs can drive shock‐like bow waves at their front. The bow waves can accelerate and heat up plasma, similar to the primary shock wave, and they play an important role in the evolution of the HSJs. In this study, we present the first simulation result concerning the formation and evolution of the bow waves, which will help us to better understand the HSJs and the magnetosheath dynamics. Key Points: We study the formation and evolution of jet‐driven bow waves with the two‐dimensional hybrid model for the first timePlasma piles up at the ramp of compressed magnetic field, causing separated peaks of density and magnetic field at the bow waveThe magnetic field structure acts as an obstacle to decelerate jet, causing the pile up of jet ions at the leading edge [ABSTRACT FROM AUTHOR]

Previous studies of rapid geomagnetic changes have highlighted the most extreme changes in direction and field strength found in paleomagnetic field models over the past 100 ky. Here we study distributions of rates of change in both time and space. Field models based on direct observations provide the most accurate values for rates of change, but their short duration precludes a complete description of field behavior. Broader representation is provided by time‐varying paleofield models, here including GGF100k, GGFSS70, LSMOD.2, CALS10k.2, HFM.OL1.A1, pfm9k.2, and SHAWQ‐iron age although variability across models and lack of temporal and spatial resolution of fine scale variations make direct comparisons difficult. For the paleofield we define rapid changes as exceeding the peak overall value of 0.4° yr−1 for directional changes and 150 nT yr−1 for intensities as established by the gufm1 model spanning 1590–1990 CE. We find that rapid directional changes are associated with low field strength and can spread across all latitudes during such episodes. Distributions of directional rates of change exhibit high skewness for models that include excursions. Rates of change in field intensity exceeding 150 nT yr−1 arise in brief intervals during the Holocene particularly associated with the strong field Levantine Iron Age Anomaly. Around the Laschamp excursion there are also rare localized occurrences of rapid intensity change. Limitations in current models make it difficult to define absolute rates for past changes, but we see that rapid changes are essential field characteristics not observed in the modern field that should nevertheless be regarded as an essential for Earth‐like dynamo simulations. Plain Language Summary: Earth's magnetic field is generated by fluid motions in its liquid outer core lying deep below the surface. Changes in the modern field are well‐mapped using low earth orbiting satellites and ground observations, but these are very modest. The largest changes over the past hundred thousand years occur on geological time scales predating the era of direct observations. These include geomagnetic excursions, periods characterized by low field strength and unstable directions, and intensity spikes when the field is unusually strong. To study the rates at which field changes occur we use a range of global time‐varying magnetic field models constructed from paleomagnetic and archeomagnetic records. These are much less detailed than modern data, but after accounting for their lesser resolution can still provide key insights into the occurrence of the most rapid changes. We find that high rates of change are an essential characteristic of the geomagnetic field over 0–100 ka that should be reproducible in Earth‐like dynamo simulations. Anomalously large rates of directional change are associated with weak field intensities surrounding geomagnetic excursions. Rapid intensity changes occur in brief intervals associated with the strongest fields found during the past few thousand years. Key Points: Rapid changes are an essential characteristic of the geomagnetic field over 0–100 kaAnomalously large rates of directional change are associated with weak field intensityRapid intensity changes occur in brief intervals associated with strong fields [ABSTRACT FROM AUTHOR]

Flux transfer events (FTEs) are transient magnetic flux ropes at Earth's dayside magnetopause formed due to magnetic reconnection. As they move across the magnetopause surface, they can generate disturbances in the ultralow frequency (ULF) range, which then propagate into the magnetosphere. This study provides evidence of ULF waves in the Pc2 wave frequency range (>0.1 Hz) caused by FTEs during dayside reconnection using a global 3D hybrid‐Vlasov simulation (Vlasiator). These waves resulted from FTE formation and propagation at the magnetopause are particularly associated with large, rapidly moving FTEs. The wave power is stronger in the morning than afternoon, showing local time asymmetry. In the pre and postnoon equatorial regions, significant poloidal and toroidal components are present alongside the compressional component. The noon sector, with fewer FTEs, has lower wave power and limited magnetospheric propagation. Plain Language Summary: The Earth's magnetosphere is a dynamic region shaped by the interplay between the solar wind and Earth's magnetic field. This interaction occurs at the boundary of the magnetosphere (magnetopause) through a process known as magnetic reconnection, giving rise to Flux Transfer Events (FTEs), which are magnetic structures that carry flux and energy into the magnetosphere. These FTEs form either in sudden bursts, patchy patterns or in a continuous, and relatively stable way making the magnetopause surface dynamic. As the FTEs move along the boundary of the magnetosphere, they create compressed regions and lead to wave generation that can extend into the magnetosphere. The study uses an advanced 3D hybrid‐Vlasov simulation model to analyze waves originated from FTE formation and propagation at the magnetopause. We find that rapidly moving and large FTEs have a significant impact on the magnetopause, leading to the generation of ULF waves with frequency above 0.1 Hz. This shows first direct evidence supporting previous theoretical speculations regarding the ability of FTEs to generate waves near the magnetopause. Key Points: Dayside Pc2 waves (>0.1 Hz) have been detected in a 3D hybrid‐Vlasov simulationThese waves exhibit lower intensity within the magnetosphere at noon, compared to the prenoon and postnoon sectorsPc2 waves observed in the simulation are associated with largest and fast moving flux transfer events initiated by subsolar reconnection [ABSTRACT FROM AUTHOR]

The past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non‐destructive method that utilizes the amplitude‐dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock‐magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude‐dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude‐dependence should ideally be demagnetized either using alternating fields or via finely‐spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples. Plain Language Summary: Oceanic basalts are ideal recorders of the Earth's magnetic field. To decipher magnetic histories recorded in rocks, paleomagnetists need to isolate the magnetization directions and intensities within rocks by one of two possible methods. One method typically involves progressively heating the samples to high temperatures. The other method involves exposing samples to alternating magnetic fields with increasing peak field intensities. Both of these methods are ultimately destructive to the original magnetization preserved within rocks. However, without knowledge of a given rock's magnetic mineralogy, randomly choosing thermal or alternating field demagnetization methods may result in high failure rates. We developed a pre‐screening method to help decide which cleaning method will likely be more successful for a given sample based on low‐field magnetic susceptibility measurements. These measurements do not affect the original magnetic information recorded in a rock, thereby permitting subsequent paleomagnetic studies on the same sample. Our technique can be performed as rapidly as 2 min per sample, is non‐destructive, and does not require complicated sample preparation. Key Points: Paleomagnetic studies utilize either alternating field or thermal demagnetization, but it is difficult to choose the best protocol a prioriAmplitude‐dependence of magnetic susceptibility measurements permits preliminary magnetic mineralogy characterization in submarine basaltsRapid amplitude‐dependence measurements may aid in deciding upon the best demagnetization protocol for submarine basalt samples [ABSTRACT FROM AUTHOR]

In this study we use micromagnetic modeling to show that the magnetizations of magnetically single‐vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single‐domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single‐vortex and equant single‐domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single‐vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity. Plain Language Summary: Magnetic minerals in rocks can record and retain magnetic information for millions of years. This magnetic information helps us to understand processes like plate tectonics and geomagnetic field behavior in the past. When rocks experience compressional forces, these affect the magnetization of the magnetic minerals within them, potentially altering this magnetic information. Previous theoretical studies of the affect of stress on magnetization used analytical theory, and predicted that stresses of >1,000 MPa are required to alter a rock's otherwise stable magnetization. We show that much lower stresses of only ∼100 MPa are required to compromise magnetic recordings in rocks. The reason for this is a change in our understanding of rock magnetic systems. Previous analytical models were for elongated particles <100 nm in size, as these were thought to be the primary carriers of stable magnetization in minerals. We now know that larger particles can retain stable magnetic recordings to high temperatures over geological time. This study shows that the magnetization of these particles are less stable than smaller particles when stresses are applied. This suggests that common geological processes such earthquakes might provide sufficient near‐surface stress to remagnetize rocks close to the fault zone, leading to a paleo‐stress recording. Key Points: Single‐vortex particles' net magnetization rotates toward the compression axis when subjected to differential stressSingle‐vortex particles display the opposite response to compressional stress compared to single‐domain particlesStress fields of only ∼100 MPa are required to alter paleomagnetic signals, lower than previously predicted [ABSTRACT FROM AUTHOR]