Search

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]

Continuous geomagnetic records of the strength and direction of the Earth's field at the surface extend back to the 1840s. Over the past two centuries, eight observatories have existed in the United Kingdom, which measured the daily field variations using light-sensitive photographic paper to produce analogue magnetograms. Around 350,000 magnetograms have been digitally photographed at high resolution. However, converting the traces to digital values is difficult and time consuming as the magnetograms can have over-lapping lines, low quality recordings and obscure metadata for conversion to SI units. We discuss our approach to digitizing the traces from large geomagnetic storms and highlight some of the issues to be aware of when capturing magnetic information from analogue measurements. These include cross-checking the final digitized values with the recorded hourly mean values from observatory year books and comparing several observatory records for the same storm to catch errors such as sign inversions or incorrect 'wrap-around' of data on the paper records. [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]

The fourth European Space Agency Earth Explorer (Swarm) was launched in 2013 and it comprises a constellation of three identical satellites. The primary mission objective is analyzing and modeling the geomagnetic field and its temporal evolution, based on the measurements of a vector and a scalar magnetometer on board. Each spacecraft (A, B, and C) carries an accelerometer, supposed to measure the non‐gravitational forces. However, this instrument did not work as expected; the processing of the related data sets has a significant latency. The focus was primarily on Swarm C, because its signal‐to‐noise ratio is the best amongst the three spacecrafts. For this satellite, the data are available for the whole mission timeline. At the end of 2021, a batch of Swarm A accelerometer data set was disseminated. Swarm A and C have flown side‐by‐side for most of the mission and, therefore, their measurements are supposed to be nearly identical after calibration. The work presented in this paper shows that such a correspondence occurs: at high frequency similar signatures are visible in both accelerometer data sets, near the equator and the poles. These features agree with measurements of other instruments on board and with earlier findings based on CHAllenging Minisatellite Payload and Gravity Recovery and Climate Experiment data. The equatorial structures show a correlation between the equatorial mass anomaly and the equatorial ionization anomaly. At the poles, the data are related to the polar cap index and to field‐aligned‐currents enhancements measured by the magnetometers on board. This research shows, for the first time, scientific results obtained from the Swarm accelerometers. Key Points: European Space Agency Swarm accelerometers data deliver for the first time scientific results in the field of thermosphere and ionosphere couplingEquatorial ionization anomaly and equatorial mass anomaly coupling visible when comparing Swarm accelerometers and Langmuir probes data setsA statistical relationship between observed field aligned current and neutral density variations is observed in Swarm accelerometers and magnetometers data [ABSTRACT FROM AUTHOR]

Field Line Resonances (FLRs) are a critical component in Earth's magnetospheric dynamics, associated with the transfer of energy between Ultra Low Frequency waves and local plasma populations. In this study we investigate how the polarisation of FLRs are impacted by cold plasma density distributions during geomagnetic storms. We present an analysis of Van Allen Probe A observations, where the spacecraft traversed a storm time plasmaspheric plume. We show that the polarisation of the FLR is significantly altered at the sharp azimuthal density gradient of the plume boundary, where the polarisation is intermediate with significant poloidal and toroidal components. These signatures are consistent with magnetohydrodynamic modeling results, providing the first observational evidence of a 3D FLR associated with a plume in Earth's magnetosphere. These results demonstrate the importance of cold plasma in controlling wave dynamics in the magnetosphere, and have important implications for wave‐particle interactions at a range of energies. Plain Language Summary: Earth's space environment is home to electrons and ions across a wide range of energies, trapped in the region by our global geomagnetic field. Energy can be transferred to and from the trapped particles through oscillations in the magnetic field, and these processes are responsible for the extreme energization of trapped electrons to hazardous levels for local spacecraft. In this paper we explore a type of magnetic field oscillation termed Field Line Resonances (FLRs): standing waves on a field line analogous to the oscillatory motion of guitar strings. We use spacecraft observations to show that the direction of the field line oscillations changes significantly depending on the density of the background plasma. The results confirm previous modeling work, and are the first observational evidence of 3D FLRs at a plume. The findings have important consequences for how FLRs transfer energy between the electrons and ions. Key Points: We present the first observational evidence of a 3D Field Line Resonance at the sharp density gradient of a plume edgeThe observed polarisation change confirms magnetohydrodynamic modeling results and predictions made by Elsden and Wright (2022)The presence of 3D Field Line Resonances during storm times has impacts for how Ultra Low Frequency waves couple and interact with local plasma [ABSTRACT FROM AUTHOR]

The ratio of O to N2 number densities (O/N2) at different altitudes is an important parameter in describing thermospheric neutral composition changes and their effects on the ionosphere during geomagnetic storms. However, storm‐induced vertical variations in O/N2 and its dependence on the O and N2 perturbations are still not fully understood. Here, the Thermosphere/Ionosphere Electrodynamics General Circulation Model simulations were used to investigate the responses of thermospheric composition at different pressure levels to the super geomagnetic storm occurred on November 20 and 21 in 2003. Our analysis shows that the behaviors of O/N2 perturbations on different pressure levels are similar above ∼180 km altitude. In the middle and low thermosphere of below ∼300 km, the storm‐time O/N2 decrease is mainly caused by a large reduction of O number density. However, N2 enhancement plays a vital role in O/N2 decreases in the upper thermosphere. The O/N2 enhancement is mainly attributed to the N2 decreases at all pressure levels. The changes of O and N2 number densities at a constant pressure level can be explained by the perturbations of their mass mixing ratio (mmr) and total mass density (ρ). The regions of the O/N2 decrease are characterized by the O mmr decrease and N2 mmr enhancement, whereas the regions of the O/N2 increase are characterized by the O mmr increase and N2 mmr decrease. The ρ value that shows the decrease globally at most pressure levels during the storm either enhance or reduce the O and N2 perturbations. Plain Language Summary: The column O/column N2 density ratio (∑O/N2) was usually used to describe thermospheric neutral composition responses to geomagnetic storms and the storm effects on ionospheric plasma density. However, thermospheric circulation changed considerably during the storm, resulting in discrepancies in composition at different altitudes. Additionally, the daytime electron density changes during geomagnetic storms are more related to those of local O/N2 at a given altitude, not the ∑O/N2. Therefore, it is important to fully understand the storm‐induced vertical variations in O, N2 and O/N2 perturbations. In this paper, the vertical variations in O/N2 and its dependence on the O and N2 perturbations during the 20–21 November 2003 storm are investigated by the numerical simulations. Our results shows that the behaviors of O and N2 perturbations depend much on the altitude, but those of O/N2 on different pressure levels are similar, especially above ∼180 km. This study helps us better understand the physical process of storm‐time ∑O/N2 variations based on the observations. Key Points: In middle and low thermosphere of below ∼300 km, storm‐time decreases of the ratio of O/N2 volume density are mainly caused by O reductionIn the upper thermosphere, N2 enhancement plays a vital role in the decreases of the ratio of O/N2 volume density during the stormAt all pressure levels, storm‐time increases of the ratio of O/N2 volume density depend more on the N2 decreases [ABSTRACT FROM AUTHOR]

A chain of magnetometers has been placed in Antarctica for comparisons with magnetic field measurements taken in the Northern Hemisphere. The locations were chosen to be on magnetic field lines that connect to magnetometers on the western coast of Greenland, despite the difficulty of reaching and working at such remote locations. We report on some basic comparisons of the similarities and differences in the conjugate measurements. Our results presented here confirm that the conjugate sites do have very similar (symmetric) magnetic perturbations in a handful of cases, as expected. Sign reversals are required for two components in order to obtain this agreement, which is not commonly known. More frequently, a strong Y component of the Interplanetary Magnetic Field (IMF) breaks the symmetry, as well as the unequal conductivities in the opposite hemispheres, as shown in two examples. In one event the IMF Y component reversed signs twice within 2 hours, while the magnetometer chains were approaching local noon. This switch provided an opportunity to observe the effects at the conjugate locations and to measure time lags. It was found that the magnetic fields at the most poleward sites started to respond to the sudden IMF reversals 20 min after the IMF reaches the bow shock, a measure of the time it takes for the electromagnetic signal to travel to the magnetopause, and then along magnetic field lines to the polar ionospheres. An additional 9–14 min is required for the magnetic perturbations to complete their transition. Plain Language Summary: Space science research has long relied on magnetometer measurements in the Northern Hemisphere to detect and observe the flow of currents in the ionosphere and magnetosphere. In the past few years it has become possible to acquire magnetic field measurements in the southern polar region as well, as a result of the placement of a chain of magnetometer stations in a remote part of Antarctica. Each of these magnetometers were placed where the Earth's magnetic field connects to an existing magnetometer in the Northern Hemisphere, on the western coast of Greenland. The locations follow a roughly north‐south meridian in geomagnetic coordinates. These "conjugate" magnetometer chains are useful for observing the similarities and differences between the ionospheric currents flowing in opposite hemispheres as a result of the solar wind's interaction with the Earth's magnetosphere. This paper presents results showing how the inter‐hemispheric measurements are very similar in some cases, but only if the signs of two of the vector components are reversed. In other cases the magnetic fields in the two polar hemispheres are different, mainly due to the summer‐winter differences in conductivity. The conjugate measurement will be useful for future space science research. Key Points: Magnetic field measurements are obtained from magnetic conjugate points in both hemispheresUnder optimal conditions the conjugate magnetic fields are very similar, with signs reversed on two components due to coordinate geometriesMore often the fields differ due to different seasonal conductivities and asymmetrical driving by the magnetic field in the solar wind [ABSTRACT FROM AUTHOR]

Tidal signatures in sporadic E (Es) layer have been confirmed by observations and simulations. However, the effect of gravity waves (GWs) on the Es layer formation process has not yet been fully understood. In this paper, the modulation of Es layers by GWs is examined through numerical simulations, in which a physics‐based model of Es layer is forced by neutral winds from the High Altitude Mechanistic General Circulation Model that can resolve GWs with horizontal wavelengths longer than 156 km (λh > 156 km). Comparison of the simulation results with and without the GWs (1,350 km > λh > 156 km) forcing reveals that the inclusion of GWs leads to short‐period (1.2–3 hr) density perturbations in Es layers, which are also seen in ground‐based ionosonde observations. At a given time, the metallic ion density at altitudes between 120 and 150 km can either increase (by up to ∼+600%) or reduce (by up to −90%) in response to GW forcing. The relative density perturbations are smaller (by up to 60%) between 90 and 120 km altitude. It is also found that the GW effect on the metallic ion density relates to the longitude, which is mostly explained by the geographical distribution of GWs activity in the mesosphere and lower thermosphere region. The longitudinal variation of the background geomagnetic field plays only a secondary role. Key Points: The modulation of Es layers by gravity waves (GWs) (1,350 km > λh > 156 km) is simulatedGWs cause short‐period (1.2–3 hr) Fe+ density perturbations, leading to production of fine structure in mid‐latitude Es layersLongitudinal dependence in Fe+ density perturbations is mainly explained by the longitudinal distribution of GWs activity in the mesosphere and lower thermosphere region [ABSTRACT FROM AUTHOR]

The low‐latitude ionosphere is a dynamic region with a wide range of disturbances in temporal and spatial scales. The Giant Metrewave Radio Telescope (GMRT) situated in the low‐latitude region has demonstrated its ability to detect various ionospheric phenomena. It can detect total electron content (TEC) variation with precision of 10−3 TECU and also can measure TEC gradient with an accuracy of about 7 × 10−4 TECU km−1. This paper describes the spectral analysis of previously calculated TEC gradient measurements and validates them by comparing their properties using two bands. The analysis tracked individual waves associated with medium‐scale traveling ionospheric disturbances (MSTIDs) and smaller waves down to wavelengths of ∼10 km. The ionosphere is found to have unanticipated changes during sunrise hours, with waves changed propagation direction as the sun approached the zenith. Equatorial spread F disturbances during sunrise hours is observed, along with smaller structures moving in the same direction. Plain Language Summary: The Earth's ionosphere can limit exploring sub‐GHz frequencies of the sky and introduces an extra phase term that is difficult to calibrate. The same calibration data can be used to study the Earth's ionosphere more precisely than conventional probes. Radio interferometry is a technique for studying astronomical sources and Earth's ionosphere by measuring the spatial coherence function of multiple elements. The GMRT is a unique instrument for exploring the equatorial ionosphere region. This study used dual‐band observations of a bright radio source with the GMRT to explore the Equatorial Ionization Anomaly region. The GMRT can detect variations in total electron content and measure TEC gradient with high accuracy. Spectral analysis was performed on TEC gradient measurements to track individual waves associated with medium scales traveling ionospheric disturbances and smaller waves up to wavelengths of about ∼10 km. The results showed unexpected changes in the ionosphere during sunrise hours and observed large plasma irregularities and smaller structures moving in the same direction. Key Points: Giant Metrewave Radio Telescope (GMRT) can demonstrate an order of magnitude better sensitivity than GNSS‐based TEC measurements in characterizing ionospheric fluctuationsThe spectral analysis technique used with GMRT can detect multiple MSTIDs and smaller‐scale structures simultaneouslyGMRT can detect ionospheric variations as small as 10 km. The study also showed waves changing direction unexpectedly during sunrise time [ABSTRACT FROM AUTHOR]

Whistler‐mode waves can modulate the electron distributions through wave‐particle interactions in the Earth's inner magnetosphere. In this paper, we have investigated the effects of the whistler waves on the electron distributions by a combination of electron magnetohydrodynamics and test‐particle simulations. Our simulations show a parallel whistler wave becomes gradually oblique during its propagation from the magnetic equator to higher latitudes. Such a whistler wave causes distinct flux increases of tens of keV electrons at large pitch angles to form electron butterfly distributions. This whistler wave traps numerous resonant electrons and transports them from lower latitudes to higher latitudes through nonlinear Landau trapping. Meanwhile, these trapped electrons are efficiently accelerated to higher energies contributing to the rapid formation of electron butterfly distributions at higher latitudes. Our study suggests nonlinear Landau trapping is a potential formation mechanism of the electron butterfly distributions observed in the Earth's inner magnetosphere. Plain Language Summary: Wave‐particle interactions are known to play an important role in regulating energetic electron distributions in the Earth's inner magnetosphere. In particular, whistler‐mode waves can efficiently modulate the electron distributions by cyclotron and Landau resonant interactions. In this paper, we used a 2‐D electron magnetohydrodynamics model to simulate a whistler wave in the dipole geomagnetic field. The simulation results indicate a parallel whistler wave becomes gradually oblique during its propagation from the magnetic equator to high latitudes. Furthermore, a test‐particle simulation shows that such a whistler wave can trap and accelerate electrons from the lower latitudes to higher latitudes by nonlinear Landau trapping, which leads to the rapid formation of electron butterfly distributions at tens of keV. Previous studies suggested that nonlinear cyclotron trapping can cause electron butterfly distributions at tens of keV observed in the Earth's magnetosphere. Our study provides a new potential formation mechanism of electron butterfly distributions in the Earth's magnetosphere. Key Points: Effects of whistler waves on electron distributions have been studied by a combination of electron magnetohydrodynamics and test‐particle simulationsA whistler wave causes distinct flux enhancements of 10s keV electrons at large pitch angles to form electron butterfly distributionsNonlinear Landau trapping contributes to the rapid formation of the electron butterfly distributions [ABSTRACT FROM AUTHOR]

Some rocks contain multiple remanence "components," each of which preserves a record of a different magnetic field. The temperature ranges over which these remanence components unblock can overlap, making it difficult to determine their directions. We present a data analysis tool called Thermal Resolution Of Unblocking Temperatures (TROUT) that treats the process of thermal demagnetization as a function of temperature (or alternating field demagnetization as a function of coercivity). TROUT models the unblocking temperature/coercivity distributions of components in a demagnetization experiment, allowing these distributions to overlap. TROUT can be used to find the temperatures/coercivities over which paleomagnetic directions change and when two directional components overlap resulting in curved demagnetization trajectories. When applied to specimens given multi‐component Thermoremanent Magnetizations (TRMs) in the laboratory, the TROUT method estimates the temperature at which the partial TRMs were acquired to within one temperature step, even for specimens with significant overlap. TROUT has numerous applications: knowing the temperature at which the direction changes is useful for experiments in which the thermal history of a specimen is of interest (e.g., emplacement temperature of pyroclastic deposits, re‐heating of archaeological artifacts, reconstruction of cooling rates of igneous bodies). The ability to determine whether a single component or multiple components are demagnetizing at a given temperature is useful for choosing appropriate ranges of temperatures to use in paleodirection/intensity experiments. Finally, the width of the range of temperature overlap may be useful for inferring the composition, grain size and domain state of magnetic mineral assemblages. Plain Language Summary: Rocks can contain records of multiple magnetization events or "components," which can tell researchers about their history. For example, if a cooled lava flow was later reheated by another lava flowing over the top of it, it will have two magnetic components for each of the cooling events. Sometimes, these components can be hard to separate from one another correctly, making it difficult to reconstruct the rocks' history. In this paper, we present a data analysis tool called Thermal Resolution of Unblocking Temperatures (TROUT) which can analyze experimental data and automatically pick out the different components. We tested TROUT on several data sets where rocks were given multiple magnetic components in the laboratory, and it accurately picks out the correct components in most cases. These test cases indicate that TROUT will be useful as an automatic tool for many applications where researchers want to know about the history of rocks they are studying. Key Points: Multi‐component demagnetization experiments can exhibit curved demagnetization data which may be difficult to interpretThermal Resolution of Unblocking Temperatures (TROUT) is a method for resolving the temperature/coercivity distributions, directions and magnitudes of components in demagnetization dataTROUT accurately estimates the temperature specimens were reheated to in laboratory experiments with curved demagnetization data [ABSTRACT FROM AUTHOR]

This paper develops a composite absolute paleointensity record for Holocene paleomagnetic secular variation (PSV) from central North America. Twelve full‐vector (inclination, declination, paleointensity) PSV records were assessed in order to build the composite record. Nine of the paleointensity records come from sediment paleomagnetic studies and are considered relative in intensity. Three of the paleointensity records come from absolute paleointensity measurements of archeological materials and lava flows. This paper develops a new method to normalize the sediment relative paleointensity records to the absolute intensity records. The final composite paleointensity record describes intensity variability over a region of Central North America delineated by 35°–48.6°N and 240.4–291.4°E (∼14° × 50°). This composite record shows a distinctive long‐duration (∼104 year) oscillation and a series of millennial‐scale intensity oscillations that are consistent over our study region. Plain Language Summary: This study develops a composite record of geomagnetic field intensity for the central North America for the last 8,000 years. This record is important for considering the total geomagnetic field variability I this region and its dynamo source(s). Key Points: We develop a new composite absolute paleointensity record for Holocene Central North AmericaWe develop a new renormalization technique to combine absolute paleointensity records and sediment relative paleointensity recordsThe final composite absolute paleointensity record has a distinctive long‐term trend and millennial‐scale variability [ABSTRACT FROM AUTHOR]

We examine coupling of fluctuations in the solar wind with electromagnetic ion cyclotron (EMIC) waves in the magnetosphere using an advanced full‐wave simulation code, Petra‐M. Dipole tilt dramatically affects the coupling process. While very little wave power can reach the inner magnetosphere without tilt effects, a tilted dipole field dramatically increases the efficiency of the coupling process. Solar wind fluctuations incident at high magnetic latitude effectively reaches the ground along the field line and mode‐convert to linearly polarized field‐aligned propagating waves at the Alfvén and IIH resonances. Therefore, solar wind compressions efficiently drive linearly polarized EMIC waves when the dipole angle is tilted toward or away from the Sun‐Earth direction. Plain Language Summary: The solar wind is emitted near the ecliptic planes, and solar wind pressure is one of the critical sources of wave activities in the Earth's magnetosphere. Since Earth's magnetic field is tilted to the ecliptic plane, compressed solar wind fluctuations can be incident over a wide range of magnetic latitudes depending on seasonal and diurnal variations. When the solar wind fluctuations reach Earth's magnetosphere, incoming wave energy can be linearly transferred to another wave mode, called a mode coupling. This paper examines the role of Earth's magnetic tilt on this mode coupling between solar wind fluctuation and electromagnetic ion cyclotron (EMIC) waves using an advanced full‐wave simulation code, Petra‐M. Without magnetic tilt, solar wind fluctuations incident at a low latitude are almost totally reflected. In contrast, solar wind fluctuations incident at high latitude can propagate efficiently into the inner magnetosphere and reach the ground. Compressional fluctuations can also be converted to linearly polarized, field‐aligned propagating waves. These results suggest that solar wind compressions can drive the linearly polarized EMIC waves and that the wave occurrence can have seasonal and diurnal dependence, which is expected to maximize at the maximum tilt of Earth's dipole into the Sun‐Earth direction. Key Points: Wave mode coupling of solar wind fluctuation to electromagnetic ion cyclotron (EMIC) waves is examined using an advanced 2D‐full wave simulation code, Petra‐MWhen the dipole magnetic field is tilted, compressional waves can reach the ground near the cusp region via mode conversionThe solar wind can drive linearly polarized EMIC waves via mode conversion more efficiently when the dipole field is tilted [ABSTRACT FROM AUTHOR]

Characterizing the location of the outer boundary of the outer radiation belt is a key aspect of improving radiation belt models and helps to constrain our understanding of the mechanisms by which the source and seed electron populations are transported into the radiation belts. In this paper, we hypothesize that there are statistical differences in the electron distribution function across the radiation belt outer boundary, and thus analyze electron flux data from the THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites to identify this location. We validate our hypothesis by using modeled electron L* values to approximately characterize the differences between electron distribution functions inside and outside of the radiation belts. Initially, we perform a simple statistical analysis by studying the radial evolution of the electron distribution functions. This approach does not yield a clear discontinuity, thus highlighting the need for more complex statistical treatment of the data. Subsequently, we employ machine learning (with no dependence on radial position or L*) to test a range of candidate outer boundary locations. By analyzing the performance of the models at each candidate location, we identify a statistical boundary at ≈8 RE, with results suggesting some variability. This statistical boundary is typically further out than those used in current radiation belt models. Plain Language Summary: Earth's magnetic field traps highly energetic particles in a donut shaped region, referred to as "the radiation belts". Our work focuses on the outer belt, comprised of electrons. Many spacecraft orbit within this region, exposing them to potential damage. To mitigate this, the radiation belts must be understood and modeled. The outer boundary is crucial to modeling, driving changes in radiation belt activity. The boundary is also important because its location helps us to understand which processes form the radiation belts. In this paper, we analyze electron data measured by satellites to identify the location of the radiation belt's outer boundary by using simple statistical methods and machine learning. Our results show that simple statistical methods cannot be used to deduce an outer boundary. Using machine learning, we test many candidate boundary locations and by quantifying the model performances at each of these locations, we are able to identify a statistical boundary location. This boundary is located at approximately eight Earth radii away from the planet, which is typically further out than the boundaries currently used by radiation belt models, although our analysis suggests the boundary location may be variable. Key Points: Simple statistical analysis of Time History of Events and Macroscale Interactions during Substorms data does not yield a boundary locationMachine learning is used to identify a boundary location using electron distribution functionsThe boundary location is found to be significantly beyond geosynchronous orbit [ABSTRACT FROM AUTHOR]

The suggestion that variations in solar irradiance affect Earth's weather and climate is based on correlations between solar and meteorological parameters. Solar activity influences the Earth's magnetic field. The geomagnetic activity index (GAI) is one of the indexes that measure this influence. In this paper, we researched the link between GAI and the passage of atmospheric cold fronts (CFs) over the Belgrade region, Serbia. Three years of daily data for solar (coronal holes, protons velocity and density), geomagnetic (GAI, electrical potential of Earth's atmosphere) and meteorological (air temperature, wind and precipitation) parameters were analysed. We developed a methodology that established pairs of GAI peaks and CFs and found the time interval (TI) between them. In 88.5% of cases, we were able to pair a GAI and a CF, while in 11.44% pairing could not be established. The number of GAI peaks without assigned CFs increased as mean values of GAI decreased. Most frequently, following an increase in the GAI, a CF passed after 7 days (relative frequency 22.8%), followed by 6 days (19.9%) and 8 days (18.5%). These three TIs covered, in sum, 61.3% of cases. Mean TI value was 6.82 days. The warm part of the year had the same TI distribution but the cold part of the year produced a bimodal frequency, with a maximum of 8 days (21.6%), followed by 5 (18.3%) and 6 days (17.6%). The most frequent CFs passing over Belgrade are from WNW‐N (67.1%) and SSW‐W (27.6%) quadrants. [ABSTRACT FROM AUTHOR]

The analysis in real time of space data variability is essential for scientists and space mission controllers. Automated tools designed to extract key descriptors of variability are needed and solutions to adapt such algorithms for on‐board computers are rare. This paper describes the design of an automated system for detecting directional discontinuities of a physical quantity and its implementation in Field‐Programmable Gate Array (FPGA). The system is currently adapted for solar wind or terrestrial magnetosheath magnetic field directional discontinuities, that is, sharp changes of the magnetic field directionality. Our detection algorithm uses analysis windows of adjustable width and averaging procedures in order to reduce the effects of random fluctuations. A sliding‐window approach is designed for continuous monitoring and detection of magnetic directional discontinuities. A software implementation of the algorithm was tested using in‐situ magnetic field measurements, and emphasized improvements of performance when using analysis windows of adjustable width. The FPGA implementation of the detection algorithm is built on DILIGENT Nexys 4 DDR featuring a commercial Xilinx Artix‐7 device and is designed to be ported to space qualified infrastructure. The FPGA system was tested with synthetic and laboratory signals, and provides results in very good agreement with the software implementation. The FPGA system provides an efficient real‐time monitoring solution using minimal computational and energy resources, and reducing the main on‐board computer utilization. Key Points: We designed an algorithm to detect directional discontinuities from in‐situ space measurements, suitable for automated applicationA Field‐Programmable Gate Array (FPGA) implementation of the algorithm, designed to be adapted for on‐board operations, is providedTests with laboratory and space measurements of the FPGA and software implementations of the detection algorithm give excellent results [ABSTRACT FROM AUTHOR]

This paper presents observations of dayside auroral signatures resulting from a massive localized compression of the magnetopause, magnetosheath, and bow shock. On 10 December 2016, the Magnetospheric Multiscale Mission (MMS) spacecraft observed a compression of the entire magnetosheath and bow shock, which moved past the spacecraft in 1 min and 45 s. Shortly afterward, the resulting auroral signature was observed at the Kjell Henriksen Observatory located in Longyearbyen, Norway. The characteristics of this unique event have major ramifications for understanding dayside magnetospheric physics. Plain Language Summary: The aurora borealis and australis are the visible signatures of interactions between the Earth's magnetic field and the solar wind. When the solar wind's magnetic field interacts with the Earth's magnetic field, there can be large fluctuations in its positioning and shape. This paper presents observations from satellites of a very large compression of the magnetic field, resulting in unique ionospheric signatures directly over an all‐sky camera at Kjell Henricksen Observatory in Svalbard, Norway. One minute and 57 s after the compression at the magnetosphere, previously unstructured aurora began to intensify and organize, first propagating eastward and then brightening westward. The auroral arcs then began to spiral in a counterclockwise direction forming a spiral structure over the field of view. This defined shape only lasted for a few seconds before dispersing and moving poleward. The characteristics of this unique event have major ramifications for understanding dayside magnetospheric physics. Key Points: Analysis of rapid compression of the magnetopause, magnetosphere, and bow shockObservations of unusual auroral signature over Svalbard, Norway resulting from compression [ABSTRACT FROM AUTHOR]

150 kilometer echoes are strong, coherent echoes observed by equatorial radars looking close to perpendicular to Earth's magnetic field. Observations over a day show a distinct necklace pattern with echoes descending from 170 km at sunrise to 130 km at noon, before rising again and disappearing overnight. This paper shows that the upper hybrid instability will convert photoelectron energy into plasma wave energy through inverse Landau damping. Using parameters from a WACCM‐X simulation, the upper hybrid wave growth rates over a day show a nearly identical necklace pattern, with bands of positive growth rate following contours of the plasma frequency. Small gaps in altitude with no echoes are explained by thermal electrons Landau damping the instability where the upper hybrid frequency is a multiple of the gyrofrequency. This theory provides a mechanism that likely plays a crucial role in solving a long‐standing mystery on the origin of 150‐km echoes. Key Points: Kinetic theory is developed for photoelectron‐driven upper hybrid instabilityUsing WACCM‐X for background parameters, the instability growth rates follow the same morphology as 150‐km echoesLandau damping by thermal electrons creates observed gaps in altitude where the upper hybrid frequency is a multiple of the gyrofrequency Plain Language Summary: For decades, large radars have observed strong, unexplained echoes returning from altitudes of 130–170 km in the atmosphere. All radars work by reflecting radio waves off a target and measuring the returned signal. For atmospheric radars, the targets are free electrons within the plasma in the upper atmosphere. Since the free electrons are typically a disordered gas, the radio waves are reflected in random directions. This means some process is needed to create a coherent structure in the plasma for the radio waves to strongly reflect back in the direction of the radar. In this paper, we show that the region between 130–170 km in the upper atmosphere is likely to create and maintain a specific set of plasma waves that act as a coherent structure for radar measurements. We show that predictions of where the plasma waves are generated match well with the observed patterns of these "150‐km echoes." This is the first research to provide a specific explanation for what causes 150‐km echoes. In understanding this cause, we learned more about the Sun's influence on our upper atmosphere while expanding the capabilities of atmospheric radars. [ABSTRACT FROM AUTHOR]

The most important driver of geomagnetic activity is the north–south (Bz) component of the interplanetary magnetic field (IMF), which dominates the solar wind‐magnetosphere coupling and all solar wind coupling functions. While the east–west (By) IMF component is also included in most coupling functions, its effect is always assumed to be symmetric with respect of its sign. However, recent studies have shown that, for a fixed value of any coupling function, geomagnetic activity is stronger for By>0 than for By<0 in Northern Hemisphere winter. In Southern Hemisphere winter, the dependence on the By sign is reversed. In this paper, we use measurements of National Oceanic and Atmospheric Administration Polar‐Orbiting Operational Environmental Satellites to show that the flux of magnetospheric electrons precipitating into the atmosphere also exhibits an explicit By dependence. This By dependence is strong in the midnight and dawn sectors where it causes a related By effect in the westward electrojet and geomagnetic activity by modulating ionospheric conductivity. Key Points: Fluxes of energetic electrons precipitating into atmosphere are strongly dependent on the sign and amplitude of IMF ByThis IMF By effect on electron fluxes is strong around midnight and at dawn but weak at duskThis IMF By effect is expected to modulate ionospheric conductivity and to affect a similar effect in geomagnetic activity [ABSTRACT FROM AUTHOR]

The geomagnetic activity index Kp is widely used but is restricted by low time resolution (3‐hourly) and an upper limit. To address this, new geomagnetic activity indices, Hpo, are introduced. Similar to Kp, Hpo expresses the level of planetary geomagnetic activity in units of thirds (0o, 0+, 1−, 1o, 1+, 2−, ...) based on the magnitude of geomagnetic disturbances observed at subauroral observatories. Hpo has a higher time resolution than Kp. 30‐min (Hp30) and 60‐min (Hp60) indices are produced. The frequency distribution of Hpo is designed to be similar to that of Kp so that Hpo may be used as a higher time‐resolution alternative to Kp. Unlike Kp, which is capped at 9o, Hpo is an open‐ended index and thus can characterize severe geomagnetic storms more accurately. Hp30, Hp60 and corresponding linearly scaled ap30 and ap60 are available, in near real time, at the GFZ website (https://www.gfz-potsdam.de/en/hpo-index). Plain Language Summary: The geomagnetic activity index Kp is a measure of planetary geomagnetic activity, expressed in units of thirds (0o, 0+, 1−, 1o, 1+, 2−, ...9o). Kp is widely used in the space physics community, as it is known to be a good proxy of the solar‐wind energy input into the magnetosphere‐ionosphere‐thermosphere system. Kp has two important limitations. One is the temporal resolution. Kp is a three‐hourly index, so that temporal features within 3 hr are not resolved. The other is the upper limit of the index. Kp does not exceed a maximum value of 9o, so that under extremely disturbed conditions, geomagnetic activity is not accurately represented. We introduce a group of new geomagnetic activity indices Hpo that overcomes these limitations. Hpo is designed to represent planetary geomagnetic activity in a similar way as Kp but with higher temporal resolution and without the upper limit at 9o. This paper describes the production of 30‐min (Hp30) and 60‐min (Hp60) indices, and demonstrates their properties in comparison with Kp. Hpo indices since 1995, including near‐real‐time values, are distributed through the GFZ website (https://www.gfz-potsdam.de/en/hpo-index). Key Points: New Kp‐like planetary geomagnetic activity indices, Hpo, are presentedHourly (Hp60) and half‐hourly (Hp30) indices are available from GFZ websiteHpo indices are open‐ended without the upper limit at 9o [ABSTRACT FROM AUTHOR]

The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 triggered atmospheric waves at all altitudes. The National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON) and European Space Agency Swarm satellites were well placed to observe its impact on the ionospheric wind dynamo. After the Lamb wave entered the dayside, Swarm A observed an eastward and then westward equatorial electrojet (EEJ) on two consecutive orbits, each with magnitudes exceeding the 99.9th percentile of typically observed values. ICON simultaneously observed the neutral wind (90–300 km altitude) at approximately the same distance from Tonga. The observed neutral winds were also extreme (>99.9th percentile at some altitudes). The covariation of EEJ and winds is consistent with recent theoretical and observational results, indicating that the westward electrojet is driven by strong westward winds in the Pedersen region (∼120–150 km). These observations imply that the dynamo is a key mechanism in the ionospheric response to the Tonga disturbance. Plain Language Summary: The January 2022 Tonga volcanic eruption caused atmospheric impacts around the world. As a natural experiment, it can be used to test our understanding of how the lower atmosphere affects space weather. Researchers are only beginning to document the chain of events post‐eruption, and this paper focuses on its impact on the generator that drives electric fields in near‐Earth space, a key part of space weather. This generator is driven by the atmosphere pushing charged particles across Earth's magnetic field. This usually creates a strong eastward current above the equator. When the Swarm A satellite coincided with the wave from Tonga, it observed that this current strengthened dramatically, then reversed. Although reversals are not unusual, this was the strongest reversal observed by Swarm since its 2013 launch, except for one large geomagnetic storm in 2015. Another satellite, the Ionospheric Connection Explorer, was luckily at the right time and place to observe related motions of the upper atmosphere, which were similarly extreme. These observations are shown to be consistent with our theoretical understanding of the generator. This study is important because it represents a critical test of atmosphere‐space interactions and implies that the Tonga eruption caused a major space weather event. Key Points: Extreme thermospheric winds and ionospheric currents were observed in coordinated space/ground‐based measurements, 10 hours post‐eruptionThe westward electrojet current when the Lamb wave reaches the dayside is consistent with recent studies of the wind‐driven electrojetObservations of linked dynamo processes provide direct evidence of the space‐weather impacts of acute lower atmospheric forcing [ABSTRACT FROM AUTHOR]

Magnetopause diamagnetic currents arise from density and temperature driven pressure gradients across the boundary layer. While theoretically recognized, the temperature contributions to the magnetopause current system have not yet been systematically studied. To bridge this gap, we used a database of Magnetospheric Multiscale magnetopause crossings to analyze diamagnetic current densities and their contributions across the dayside and flank magnetopause. Our results indicate that the ion temperature gradient component makes up to 37% of the ion diamagnetic current density along the magnetopause and typically opposes the classical Chapman‐Ferraro current direction, interfering destructively with the density gradient component, thus lowering the total diamagnetic current density. This effect is most pronounced on the flank magnetopause. The electron diamagnetic current was found to be 5–14 times weaker than the ion diamagnetic current on average. Plain Language Summary: The solar wind represents a continuous outflow of charged particles from the Sun's upper atmosphere into the solar system. Upon reaching Earth's magnetosphere, the solar wind's dynamic pressure is balanced by the magnetic pressure of Earth's magnetic field in a boundary layer known as the magnetopause. This boundary layer represents the entry point of the solar wind's energy into Earth's magnetosphere and upper atmosphere, playing a crucial role in energy transport throughout the interconnected system. Plasma density and temperature differences across the boundary layer generate an electric current that supports the magnetopause. In this paper, we clarify the physical mechanism of the magnetopause current by using high‐resolution data from NASA's Magnetospheric Multiscale mission. We found a significant ion temperature contribution to the magnetopause current not identified in previous studies. Our results also indicated that the plasma electrons' contribution to the magnetopause current was significantly smaller than the ion contribution. Key Points: The magnetopause diamagnetic current is composed of opposing density and temperature gradient generated componentsThe temperature gradient contributes up to 37% of the ion diamagnetic current density along the magnetopauseThe temperature component typically opposes the classical Chapman‐Ferraro current direction [ABSTRACT FROM AUTHOR]

This paper reports a special midlatitudinal medium‐scale traveling ionospheric disturbance (MSTID) event, accompanied by a poleward surge of airglow depletion/enhancement and a bifurcation of depletion during the magnetically quiet period. These special structures were generated during a decreasing height of ionosphere with nighttime plasma density enhancement and increment of airglow emission intensity possibly caused by a passing‐by midnight brightness wave. We suggest that the interaction of the passing‐by MSTID and nighttime plasma density enhancement resulted in the poleward surge and bifurcation of airglow depletion. The nighttime plasma density enhancement could feed the high plasma density to interact with the airglow depletions of MSTID, causing the poleward surge and bifurcation of airglow depletion by the secondary gradient drift instability. The poleward surged airglow enhancement within two adjacent depletions of MSTID is also firstly reported in this study. Plain Language Summary: It was generally believed that the midlatitudinal ionosphere is fairly quiescent until the first report of airglow structure of the medium‐scale traveling ionospheric disturbance by Garcia, Kelley, Makela, and Huang (2000, https://doi.org/10.1029/1999JA000305). Kelley et al. (2000, https://doi.org/10.1029/2000GL000022) and Garcia, Kelley, Makela, Sultan, et al. (2000, https://doi.org/10.1029/1999JA000306) further reported magnetically storm‐time "intense mid‐latitude spread F" events accompanied by poleward surged bifurcations of airglow depletions, which caused the severe perturbations of GPS signal. Those two events were most likely the interactive result of airglow depletion and enhanced plasma density region from the equatorial ionization anomaly crest region driven by magnetic storms. In this paper, we report a very similar airglow event accompanied by a poleward surged airglow depletion/enhancement and a bifurcation of depletion but occurred at magnetically quiet time in Xinglong, China. We suggest that the interaction of the passing‐by medium‐scale traveling ionospheric disturbance and the nighttime plasma density enhancement/nighttime increment of airglow emission intensity from a possible source of midnight brightness wave resulted in the poleward surged bifurcation of aiglrow depletion, most likely driven by the secondary gradient drift instability. This event can broaden our knowledge on the dynamical process of midlatitudinal ionosphere and provide a new guidance for further investigation of the midlatitudinal special airglow events. Key Points: MSTID with a poleward surged airglow depletion/enhancement and a bifurcation of depletion occurred during the magnetically quiet timeSecondary gradient drift instability could have developed the poleward surged bifurcation of depletionThis event is suggested to be caused by the interaction between MSTID and NPDE [ABSTRACT FROM AUTHOR]

This paper is a statistical survey of polar cap patches in relation to solar and geomagnetic activity. Ten thousand six hundred eighty‐eight patches have been identified from in situ plasma observations of the Defense Meteorological Satellite Program F16 satellite for 14 years (2005–2018). These patches are divided into two groups: (a) cold patches, which consist of dense but cold plasma; and (b) hot patches, which consist of dense but hot plasma. The statistical results indicate that (a) the occurrence of cold patches is clearly dependent on solar and geomagnetic activity, but hot patches don not show such dependence; (b) both cold and hot patches preferably appear in the winter season; (c) the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activity; (d) the spatial size of cold patches appears larger than that of hot patches under similar solar and geomagnetic activity. Plain Language Summary: Polar cap patches are localized regions of enhanced plasma density in the polar ionosphere. They are associated with strong electron density gradients resulting in non‐negligible ionospheric scintillations for satellite communication and navigation systems. To characterize polar cap patches and investigate their statistical dependence on solar and geomagnetic activity, 10,688 patches have been identified from 14 years of in situ Defense Meteorological Satellite Program satellite plasma observations. These patches have been divided into cold and hot patches. We find that cold patches occur more frequently during solar maximum years. The spatial size of cold and hot patches decreases with solar activity (increases with geomagnetic activity). Furthermore, the spatial size of cold patches is larger than that of hot patches under similar solar and geomagnetic activity. Key Points: The occurrence of cold patches is clearly dependent on solar and geomagnetic activity, while hot patches do not show such dependenceIn NH winter, the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activityIn NH winter, the spatial size of cold patches appears larger than that of hot patches under similar solar and geomagnetic activity [ABSTRACT FROM AUTHOR]

The Cretaceous Normal Superchron (CNS), defined as a magnetic quiet zone spanning from ∼126 to ∼84 Myr, is often used to understand the Earth's geodynamo processes. However, whether there were polarity reversals within the CNS remains contentious. This paper presents the youngest detrital zircon U‐Pb age‐constrained magnetostratigraphic study of the Cretaceous Khorat Group for two sections (i.e., Ban Phonngam (BP) and Ban Nongpen (BN)) in Vientiane, Laos. Both sections are characterized by the prominent long normal‐polarity zones that are correlated to the CNS. Interestingly, six (four) short primary reversed horizons were identified within the BP (BN) section. Integrated with other reported reversed events, there likely at least five globally and two single reported reversed‐polarity events or clusters of events have happened within the CNS. The confirmation of frequent reversed polarities within the two parallel sections will provide a new comprehensive understanding of the Earth's geodynamic behavior during the CNS. Plain Language Summary: The Cretaceous Normal Superchron (CNS) was defined as a single normal‐polarity zone within the Cretaceous at ∼126–84 Ma. Geomagnetic field behaviors during this interval can help understand the geodynamic processes within the Earth's interior. But whether, when, and how often have the polarity reversals occurred within the CNS are still controversial yet fascinating. Here, we report a high‐resolution magnetostratigraphic study on the Cretaceous Khorat Group from two parallel outcrop sections (i.e., Ban Phonngam (BP) and Ban Nongpen (BN)) in the Vientiane Basin, Laos. Both sections show the distinct long normal‐polarity zones, which are correlated to the CNS under the constraints of youngest detrital zircon U‐Pb ages and regional geochronological evidence. It is interesting that six and four short episodes of primary reversed polarity were observed in the BP and BN sections, respectively. By summarizing the worldwide records of polarity reversals in marine, volcanic, and terrestrial rocks within the CNS, we believed that there likely at least five globally and two single reversed‐polarity events or clusters of events have taken place within the CNS. Our work provides new insights into the geomagnetic field characteristics during the CNS, which could guide the future geodynamo simulations. Key Points: Two parallel sections in the Vientiane Basin that are characterized by prominent long normal‐polarity zones are correlated to the Cretaceous Normal Superchron (CNS)The robust short reversed horizons indicate true short‐lived geomagnetic field reversals within the CNSAt least five globally and two single reported reversed‐polarity events or clusters of events have happened within the CNS [ABSTRACT FROM AUTHOR]

We present results of analysis of lightning observations and satellite measurements of ionospheric magnetic field fluctuations in the ultralow frequency (ULF) range. The fluctuations are measured by Swarm satellites, while the lightning observations are provided by the Geostationary Lightning Mapper (GLM) and the World ELF Radiolocation Array (WERA). We identify spatio‐temporal relationships that demonstrate a leakage of electromagnetic fluctuations caused by lightning into the upper ionosphere. Causal association between the two phenomena is evidenced by investigating relations between lightning and fluctuation properties. The presented results suggest that lightning generate ULF fluctuations in the ionosphere that can be detected by satellites, if the lightning‐satellite geographic distance is less than ∼5°. Typical properties of the fluctuations caused by lightning are described in the paper. To our knowledge, this is the first direct experimental confirmation of a link between lightning and magnetic field fluctuations in the upper ionosphere in the ULF range. Plain Language Summary: It has been a matter of interest, if electromagnetic fluctuations caused by lightning can propagate from the lower atmosphere higher into the ionosphere, which is an ionized and electrically conducting medium. This process requires conversion of the electromagnetic perturbation propagating in the neutral atmosphere into an ionospheric plasma wave, which for ultralow frequencies (ULF) can attenuate strongly the wave amplitude. The attenuation is considered to be rather significant, thus one could argue that it is virtually not possible to observe the ionospheric magnetic field perturbations caused by lightning using currently available satellite magnetometers. There are many remote observations of lightning and direct satellite measurements of ionospheric magnetic field fluctuations, that can be analyzed searching for a possible link between the two phenomena. Using Swarm satellite measurements and two types of lightning observations, we provide an evidence that lightning generate electromagnetic perturbations that propagate into the upper ionosphere and can be measured with magnetometers onboard low‐Earth orbit satellites, for example, by the Swarm constellation. We reveal links between lightning and ionospheric wave properties, that suggest a real causality relationship between the two phenomena. To our knowledge, this is the first direct experimental confirmation of such a relation in the ULF range. Key Points: Lightning can generate ultralow frequency (ULF) fluctuations leaking into the upper ionosphereObservations show that the fluctuation amplitude is proportional to the lightning charge momentThe ULF fluctuations generated by lightning can be detected by low‐Earth orbit satellites, for example, the Swarm constellation [ABSTRACT FROM AUTHOR]

The storm‐time ring current is formed by the inward convection of the near‐earth plasma sheet, so understanding the changing source of the plasma sheet is key for understanding ring current development. The ionospheric and solar wind sources can be distinguished by the charge state of the heavy ions; solar wind ions are highly iononized, while ionospheric ions are predominantly singly ionized. AMPTE/CHEM measurements are used to track the changing composition in the 6–9 Re plasma sheet as a storm develops in order to determine the fraction of the population that comes from each source. We find that prior to the storm, the solar wind source dominates. During the storm main phase, the solar wind contribution decreases, while the ionospheric contribution increases, making the source predominantly ionospheric. The source returns to predominantly solar wind plasma during the recovery phase. Plain Language Summary: The ions trapped in the earth's magnetic field have two possible sources: the sun or the earth's ionosphere. A stream of ionized particles from the sun called the solar wind is constantly moving outward, flowing by the earth. These particles can enter the earth's magnetosphere and become trapped. Ions can also be accelerated out of the ionosphere into the magnetosphere. The interplay between these two sources is not well understood. In this paper, we test how the source changes as a large geomagnetic storm develops. We find that the source switches from being dominantly solar wind, to dominantly ionospheric during the peak of the storm. Key Points: Ionospheric and solar wind sources to the near‐earth plasma sheet are tracked during one storm using the AMPTE/CHEM instrumentThere is a sharp change from a predominantly solar wind to ionospheric source during both intensifications in the storm's main phaseThe source changes back to predominantly solar wind during the recovery phase [ABSTRACT FROM AUTHOR]

Flux transfer events (FTEs), as flux ropes (FRs), are considered key agents for solar wind energy to enter the terrestrial magnetosphere. Recent observations identify entangled flux tubes that collide and pull against each other. Reconnection occurs to disentangle and produce a new pair of FRs with different connectivity. In this paper, we examine the entanglement interface and how such an entanglement process evolves in time by comparing 17 entanglements observed by the Magnetospheric Multiscale (MMS) mission. The By‐dominated interplanetary magnetic field (IMF) distribution of the 17 events agrees with previous findings. We have identified three evolutionary stages characterized by the magnetic field and pressure enhancement. Our study confirms the FR nature of these events and explains how a disparate pair of ropes is formed from two entangled flux tubes, each initially connected to a different hemisphere of the magnetosphere. Plain Language Summary: The Earth's intrinsic magnetic field deflects the solar wind flow at a boundary called the magnetopause. Near this boundary, twisted flux tubes are found. Such tubes may become entangled if they move toward each other, say, from the Southern and Northern Hemispheres. This study analyzes 17 such events and identifies three evolutionary stages as the entanglement proceeds. The results improve our understanding of not only the complex coupling between solar wind and the Earth's magnetic field but other similar processes in space plasma. Key Points: IMF clock angles associated with 17 flux tube entanglement events present peaks near horizontal directionThe entanglement process evolves in three distinguishable stagesMagnetic tension force contributes to the pressure balance at the entanglement interface [ABSTRACT FROM AUTHOR]

Simultaneous eastward and westward traveling surges were observed at Tjörnes, Iceland, and Syowa station, Antarctica, respectively. Several remarkable differences were identified. (1) The position of the initial bright spot was shifted by 1.7 to 2.3 MLT between both hemispheres. (2) The surges differ in traveling speed between the eastward traveling surge (6.5 km s−1) and the westward traveling surge (1.3 km s−1). (3) The Arase satellite was located on a geomagnetic field line connecting both ground stations and observed a significant excess in westward component of the magnetic field, which is consistent with the large shifts of the initial bright spots in both hemispheres. (4) The background Hall current flows eastward (Northern Hemisphere) and westward (Southern Hemisphere). The observed north‐south asymmetry of the traveling surges suggests that the ionosphere can play an essential role in controlling the fundamental spatiotemporal development of auroras in both hemispheres. Plain Language Summary: Occasionally, the aurora suddenly brightens in local areas of the Northern and Southern Hemispheres, causing explosive and widespread phenomena. At this time, it is known that a part of the aurora travels toward east or west from the point of the explosion; however, the formation mechanism of this traveling aurora is unknown. Recently, this traveling aurora has been reproduced by computer simulation, and it has been shown that the direction of its traveling is determined by the state of the ionosphere rather than by the projected motion of the source region in the magnetosphere. In this paper, we observed traveling auroras with two identical high‐speed cameras installed in the Northern and Southern Hemispheres simultaneously and clarified for the first time that the state of the ionosphere determines the direction of the traveling aurora. Understanding the mechanism of such connection between the space and the Earth is important for predicting the space environment required for various human activities and technologies using the space. Key Points: An auroral breakup was captured simultaneously by ground‐based all‐sky cameras at magnetically conjugate stations in both hemispheresThe auroral surge evolved asymmetrically regarding the longitudinal direction in both hemispheresThe surge evolved in the direction of the ionospheric Hall current, which is consistent with the expectation from a global simulation [ABSTRACT FROM AUTHOR]

Ducting Pc1 waves are observed over a wide latitudinal range by the low‐Earth orbit satellites as compressional mode. In this paper, we present the first observation of the modulation of ducting Pc1 waves by equatorial plasma bubbles (EPBs) based on the Swarm satellites. We show two ducting Pc1 events propagating across EPBs that occurred on 7 April 2016 and on 27 September 2017. We found that the EPBs modulate the Pc1 wave propagation by setting up reflection boundaries and leakage holes in the ionospheric waveguide. We also found that changes of Pc1 wave intensities generally follow the electron density variation and that the intensity is stronger at higher density region. From the comparison between Swarm‐A and Swarm‐C observations, we conclude that ionospheric plasma plays an important role for Pc1 waveguide even though their density is significantly low in EPBs. Plain Language Summary: Pc1 (or electromagnetic ion cyclotron) waves have been observed across the whole magnetospheric and ionospheric regions and on the ground with different characteristics. Typically, they propagate along the magnetic field line in the magnetosphere. But once the waves enter the ionosphere, plasma effects such as mode conversion and reflection complicate their propagation. One of the Pc1 wave propagation characteristics on the ionosphere is ducting (waveguide). Ionospheric ducting is a way radio waves can travel thousands of kilometers along an ionospheric layer. Ducting is controlled by various physical processes and ionospheric conditions, among which plasma density is one of the factors. In this study, we present the first observations of the ducting Pc1 wave controlled by ionospheric electron density, particularly by the equatorial plasma bubbles, which are localized density depletion near the geomagnetic equator. Our observation results show that the Pc1 wave intensity in the ionosphere strongly depends on the ambient electron density. Key Points: We report the first observation of the modulation of ducting Pc1 wave by equatorial plasma bubbles based on the Swarm satellitesEquatorial plasma bubbles modulate Pc1 wave propagation by setting up boundaries and holes in the ionospheric waveguideIonospheric plasma plays an important role as a Pc1 waveguide even though their density is significantly low in plasma bubbles [ABSTRACT FROM AUTHOR]

SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) is a space mission which aims to measure Earth's global system responses to solar wind and geomagnetic variations with innovative instrumentation, for example, wide–field X‐ray telescope of Lobster–Eye type, on board. It is a collaborative project of the European Space Agency and the Chinese Academy of Sciences. The SMILE international consortium involves the Czech Technical University in Prague and the Czech teams are expected to contribute to the project, mainly to the science and software related to the X–ray telescope. The aim of this short paper is to provide an outline of SMILE and in particular of the Czech participation to this mission, with emphasis on observation of celestial X‐ray sources as SMILE secondary science. [ABSTRACT FROM AUTHOR]

So‐called "Steve" subauroral purple emissions have recently been uncovered by auroral photographers and have rapidly become an intense subject of debate as to their origin. In some events, nearby periodic green emissions have also been uncovered and given the name "picket fence," owing to their appearance. The present paper advances our understanding of these phenomena by narrowing down the altitude extent of the Steve and picket fence emissions. Our determination is based on the event of 16 September 2017, which was simultaneously observed from two vantage points, allowing for a determination of the height range of Steve and picket fence through triangulation. We show that the picket fence extend between 95‐ and 150‐km altitude and is aligned with the geomagnetic field, while the Steve altitude spread is between 130 and 270 km. We also show the two phenomena to be on nearby or perhaps the same magnetic field lines. Key Points: The optical emissions of Steve range from 130 to 270 km in altitudeThe optical emissions of the green Picket Fence range from 95 to 150 km in altitudeSteve and the Picket Fence extend vertically along similar magnetic field lines [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]

Data are analyzed from a Magnetospheric Multiscale encounter with a dayside magnetopause reconnection region on 29 December 2016. The uniqueness of the event stems from the small (~7 km) average spacecraft separation and the sequential sampling of an electron diffusion region with electron crescent distributions. We quantitatively investigate the earthward acceleration of magnetosheath electrons through the in‐plane null by the polarization electric field EN that points radially outward from the magnetopause. The results compare favorably with previous plasma simulations with one important difference that the reconnection electric field (EM) extends throughout the region of strong EN so that both fields energize electrons in the same region. This acceleration is quantified here for the first time. As the spacecraft penetrate deeper into the region of enhanced EN, the magnetic reflection of lower‐energy electrons produces a thinner crescent. Plain Language Summary: Reconnection causes the conversion of magnetic energy to particle energy and the breaking and reconnection of solar wind and geomagnetic field lines. In asymmetric reconnection at the dayside magnetopause with different plasma densities and magnetic field strengths on the Earth and Sun sides of an X‐line, this energy conversion is displaced to the earthward side of the current layer. An electric field pointing outward normal to the dayside magnetopause drives reconnection by accelerating solar wind electrons across the reconnection current sheet. These electrons take up dawnward‐directed meandering orbits, and they are ultimately the carriers of the reconnection current. This paper reports the first direct measurement of this acceleration. Key Points: Parallel and perpendicular energy conversion and electron acceleration are studied with data from four spacecraft with average separations of 7 kmThe magnetopause normal electric field (EN) accelerates magnetosheath electrons across the reconnection current sheet to form crescent distributionsMagnetic reflection causes the crescent energy peaks to become narrower with increasing depth into the diffusion region [ABSTRACT FROM AUTHOR]

This paper reports on new results in the determination of magnetic signals produced by oceanic tides as estimated from satellite magnetic measurements. We find that combining data from the past CHAMP (2000–2010) and the present Swarm (since 2013) satellite missions significantly improves the quality of the extracted tidal signals, in particular if along‐track and cross‐track magnetic "gradient" data are utilized. This allows us to determine the magnetic signature not only of the M2 tide but also of the much weaker N2 and O1 tidal constituents. To minimize disturbances from magnetospheric and ionospheric currents, we only use data from the nightside region during geomagnetic quiet conditions and remove core, crustal, and magnetospheric field contributions as given by the CHAOS geomagnetic field model. Despite their small magnitudes, all determined tidal constituents show sensitivity to the electrical conductivity profile of the underlying mantle, enabling imaging the upper mantle below the oceans. Key Points: Global models of the magnetic signals produced by the M2, N2, and O1 oceanic tides have been extracted from satellite magnetic measurementsCombining data from the Swarm and CHAMP missions as well as using field gradient plays key role in the robustness of the estimated modelsAll tidal constituents show significant sensitivity to the electrical conductivity of the oceanic mantle [ABSTRACT FROM AUTHOR]

With the increment of grid complexity and voltage level, the effect of geomagnetic induced current (GIC) on the grid is also increasing. There is no complete system to assess the impact of GIC on the reliability of the grid at present. This paper discusses the relationship between geomagnetic data and transformer failure rate. Referring to the existing mathematical model between GIC indices and failure rate, Monte–Carlo method is used to calculate the reliability of a given system under the influence of geomagnetic storm. The case study shows the validity of the assessment and this paper contributes to the establishment of a complete reliability evaluation system. [ABSTRACT FROM AUTHOR]

A numerical study of the effects of seismically generated acoustic waves in the ionosphere is conducted using a three‐dimensional (3‐D) ionospheric model driven by an axisymmetric neutral atmospheric model. A source consistent with the 2011 Tohoku earthquake initial ocean surface uplifting is applied to simulate the subsequent responses. Perturbations in electron density, ion drift, total electron content (TEC), and ground‐level magnetic fields are examined. Results reveal strong latitude and longitude dependence of ionospheric TEC, and of ground‐level magnetic field perturbations associated with acoustic wave‐driven ionospheric dynamo currents. Results also demonstrate that prior two‐dimensional models can capture dominant meridional responses of TEC over latitude, even though dynamics at other longitudes are not resolved. Conclusions support that TEC and magnetic signatures can arise from nonlinear acoustic waves generated by strong earthquakes; simulations elucidate the comprehensive physics of their 3‐D ionospheric responses. Plain Language Summary: This paper reports new numerical model results on how the ionosphere—the ionized, conducting region of the upper‐atmosphere—responds to strong acoustic waves launched by earthquakes. The effects of these waves in the ionosphere can be observed from ground: They are measured as variations in Global Positioning System satellite signals received at the ground, which translate to variations in integrated electron content of the ionosphere. They can be detected also via small fluctuations in magnetic field, which are driven by ionospheric currents. The model results suggest that both measurement techniques can provide insight into the waves and their sources; new guidance for interpreting these measurements is provided. Further, results demonstrate a new capability for simulating these processes in three dimensions, which can be applied to more‐realistic case studies. Key Points: Earthquake‐driven TEC and magnetic perturbations are studied with a 3‐D modelMagnetic fluctuations driven by infrasonic acoustic waves are detectableLocal geomagnetic field geometry affects directionality of TEC responses [ABSTRACT FROM AUTHOR]

Pc3 range frequency (22–100 mHz) auroral pulsations often occur at daytime high latitudes, equatorward of the cusp/cleft and typically map to the dayside outer magnetosphere. In this paper we present simultaneous observations of compressional Pc3 magnetic pulsations in the dayside outer magnetosphere that occurred in direct association with daytime Pc3 auroral pulsations at South Pole Station (−74.4° magnetic latitude). The pulsations were almost identical at the two locations, and their correlation was clearest when the magnetospheric pulsations were highly monochromatic. Lower‐band chorus waves and keV electron fluxes were also modulated in the Pc3 range, likely by the compressional magnetic pulsations. The common Pc3 frequency in the magnetosphere and aurora matched well with the predicted frequency of upstream ultralow frequency waves. These results provide the first compelling evidence for the direct dayside outer magnetosphere‐ionosphere linkage between upstream‐generated compressional Pc3 waves, Pc3 range modulations of chorus waves and keV electrons, and Pc3 auroral pulsations. Plain Language Summary: South Pole Station, Antarctica (SPA), is a unique polar observatory, which can monitor dayside aurora from the ground throughout austral winter. High time resolution optical instruments at SPA frequently capture auroral pulsations with Pc3 frequencies (22–100 mHz) around the midday hours. Here we use unique conjunctions of ~2‐Hz SPA all‐sky camera and Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft to identify the origin of the periodicity of daytime Pc3 auroral pulsations observed at SPA and their driver in the magnetosphere. Simultaneous in situ measurements in the dayside outer magnetosphere observed identical Pc3 magnetic pulsations in the compressional component. Lower‐band chorus waves and keV electron fluxes were observed to be modulated also with the Pc3 range. The common Pc3 frequency in the magnetosphere and ionosphere matched well with the expected frequency of upstream ultralow frequency (ULF) waves generated in the foreshock region. The simultaneous SPA‐THEMIS spacecraft conjunctions provide, for the first time, direct evidence that upstream‐origin compressional Pc3 magnetic pulsations drive daytime auroral pulsations through wave‐particle interactions. One important implication of this study is that the high temporal cadence 2‐D observations of daytime auroral pulsations can be a useful tool for remote sensing the dynamics of outer magnetospheric Pc3 ULF waves. Key Points: Daytime auroral pulsations have a one‐to‐one correspondence with compressional Pc3 magnetic pulsations in the outer magnetosphereIn situ lower‐band chorus waves and keV electron fluxes are modulated by the compressional Pc3 magnetic pulsationsUpstream ULF waves are one of the most influential sources that control the frequency of the daytime auroral pulsations [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]