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Dedicated scientific measurements of the strength and direction of the Earth's magnetic field began at Greenwich and Kew observatories in London, United Kingdom, in the middle of the nineteenth century. Using advanced techniques for the time, collimated light was focussed onto mirrors mounted on free‐swinging magnetized needles which reflected onto photographic paper, allowing continuous analog magnetograms to be recorded. By good fortune, both observatories were in full operation during the so‐called Carrington storm in early September 1859 and its precursor storm in late August 1859. Based on digital images of the magnetograms and information from the observatory yearbooks and scientific papers, it is possible to scale the measurements to International System of Units (SI units) and extract quasi‐minute cadence spot values. However, due to the magnitude of the storms, the periods of the greatest magnetic field variation were lost as the traces moved off‐page. We present the most complete digitized magnetic records to date of the 10‐day period from 25 August to 5 September 1859 encompassing the Carrington storm and its lesser recognized precursor on 28 August. We demonstrate the good correlation between observatories and estimate the instantaneous rate of change of the magnetic field. Plain Language Summary: The Carrington storm of September 1859 is one of the largest known geomagnetic storms in the historic record. Two observatories in London were operating at the time and by good fortune both recorded the extreme geomagnetic storm on paper records. These are held at the British Geological Survey and have been made available online as digital images. The next step is to digitally trace over the magnetograms to produce useful digital values. However, scaling the values of digital pixels to International System of Units (SI units) of degrees of angle and nanoTesla is not easy as the original scaling factors are not available. We use a mixture of written reports at the time and notes from the observatory yearbooks to track down plausible scaling factors and to explain the process of digitization of very old records. The data for 10 days covering 25 August to 5 September 1859 are now available for other researchers to use. Key Points: Continuous magnetogram traces are available in London, United Kingdom for August and September 1959Serendipitously, two observatories recorded the Carrington flare and the subsequent stormWe digitize the archive paper records to produce a correctly timed and scaled digital set of digital values for further analysis [ABSTRACT FROM AUTHOR]

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]

On 3 July 2021, an X1.5 solar flare from the National Oceanic and Atmospheric Administration solar Active Region AR12838 (24°N, 88°W) occurred at 14:18 UT, peaked at 14:29 UT, and decayed at 14:34 UT. The study of this X1.5 solar flare is significant due to its unique geomagnetic crochet feature at high latitudes and its effective signature on Earth. The study examined X‐rays, the extreme ultraviolet spectrum, ionospheric equivalent current (IEC), and geomagnetic field components. The study reveals a sudden increase in IEC during the X1.5 flare episode, forming a zonal current region and producing a geomagnetic crochet signature in geomagnetic field components at high latitudes (50°–80°N) along the 11°–26°E longitude sector during the flare peak time. All three geomagnetic field components show different sensitivity to the solar flare effect (sfe), and the amplitude and phase of the geomagnetic crochet across latitudes (for a given longitude) are consistent with the variations in the IEC. The present study is the first to appraise geomagnetic crochets of low magnitude (8–40 nT) and short duration (10–15 min) at high latitudes, particularly in the polar cusp region, during the X‐class limb flare. Plain Language Summary: The X1.5 solar flare at 14:18 UT on 3 July 2021, occurred in a newly formed solar active region AR12838 (24°N, 88°W) on the sun. The current study analyses the solar flare effect (sfe) signature at high latitude induced by an X1.5 flare, and compares the results from previous paper of Yamauchi et al. (2020, https://doi.org/10.5194/angeo-38-1159-2020). However, while that paper reported geomagnetic crochet of high amplitude (200 nT) and long duration (∼2 hr), the present work reports geomagnetic crochet of small amplitude (40 nT) and short duration (∼15 min). The current study is unique regarding observations of geomagnetic crochet in the polar cusp region. Key Points: An X1.5‐class solar flare was recorded on 3 July 2021, from the newly emerged solar active region NOAA AR12838 over the solar limbThe current study examines the solar flare effect at high latitude magnetometer stations, an aspect that has not been extensively studiedUnique signatures of Cusp geomagnetic crochet of small amplitude and short duration are observed [ABSTRACT FROM AUTHOR]

Submarine cables have experienced problems during extreme geomagnetic disturbances because of geomagnetically induced voltages adding or subtracting from the power feed to the repeaters. This is still a concern for modern fiber‐optic cables because they contain a copper conductor to carry power to the repeaters. This paper provides a new examination of geomagnetic induction in submarine cables and makes calculations of the voltages experienced by the TAT‐8 trans‐Atlantic submarine cable during the March 1989 magnetic storm. It is shown that the cable itself experiences an induced electromotive force (emf) and that induction in the ocean also leads to changes of potential of the land at each end of the cable. The process for calculating the electric fields induced in the sea and in the cable from knowledge of the seawater depth and conductivity and subsea conductivity is explained. The cable route is divided into 9 sections and the seafloor electric field is calculated for each section. These are combined to give the total induced emf in the cable. In addition, induction in the seawater and leakage of induced currents through the underlying resistive layers are modeled using a transmission line model of the ocean and underlying layers to determine the change in Earth potentials at the cable ends. The induced emf in the cable and the end potentials are then combined to give the total voltage change experienced by the cable power feed equipment. This gives results very close to those recorded on the TAT‐8 cable in March 1989. Plain Language Summary: Submarine cables carry a significant amount of international internet traffic, so any disruption to their operation could have widespread consequences. In the past, trans‐Atlantic phone calls have been heard alternately as shrieks and whispers as geomagnetically induced voltages added or subtracted from the power feed for the cable repeaters used to amplify the signals. Modern submarine cables transmit the signals along optical fibers but still have a copper conductor along the cable to carry power to the repeaters, so continue to be subject to voltages induced by disturbances of the Earth's magnetic field. This paper re‐examines the process of geomagnetic induction in the sea and submarine cables. It is shown that this involves both the production of an induced electromotive force (emf) in the cable itself as well as induction in the seawater that leads to a change in the potential of the land at each end of the cable. Example calculations are made for the TAT‐8 trans‐Atlantic cable and compared to measurements made on the cable during 13 and 14 March 1989, the largest magnetic storm of the 20th century. Key Points: Geomagnetic disturbances induce electric fields in both the sea and in submarine cablesEarth potentials are produced by the geoelectric coast effect at each end of a cable routeVoltages experienced by submarine cables are due to both the induced electric fields and earth potentials at the ends [ABSTRACT FROM AUTHOR]

Data products relating to auroral arc systems are often sparse and distributed while ionospheric simulations generally require spatially continuous maps as boundary conditions at the topside ionosphere. Fortunately, all‐sky auroral imagery can provide information to fill in the gaps. This paper describes three methods for creating electrostatic plasma convection maps from multi‐spectral imagery combined with plasma flow data tracks from heterogeneous sources. These methods are tailored to discrete arc structures with coherent morphologies. The first method, "reconstruction," builds the electric potential map (from which the flow field is derived) out of numerous arc‐like ridges that are then optimized against the plasma flow data. This method is designed for data from localized swarms of spacecraft distributed in both latitude and longitude. The second method, "replication," uses a 1D across‐arc flow data track and replicates these data along a determined primary and secondary arc boundary while simultaneously scaling and rotating to keep the flow direction parallel to the arc and the flow shear localized at the arc boundaries. The third, "weighted replication," performs a replication on two data tracks and calculates a weighted average between them, where the weighting is based on data track proximity. This paper shows the use of these boundary conditions in driving and assessing 3D auroral ionospheric, multi‐fluid simulations. Plain Language Summary: The aurora, or northern and southern lights, are embedded within a complicated system of interacting electric fields, magnetic fields, and charged particles, the more energetic of which produce the lights themselves by exciting the neutral atmosphere. This brings about a 3D electric current system. These currents enter and exit the atmosphere along the Earth's magnetic field lines, and can only close their circuit between 80 and 150 km. This paper outlines the importance of simulating auroral arc systems in 3D and thus the need for generating continuous horizontal top‐boundary drivers for these simulations. This is difficult as the available data products are limited. This paper provides three methods for creating these boundary conditions using multi‐color, all‐sky auroral imagery in conjunction with approximately across‐arc plasma flow data tracks provided by spacecraft, sounding rockets, and/or radar measurements. Key Points: We provide three methods for developing ionospheric convection flow maps from limited data tracks in conjunction with auroral imageryMethods for generating distributed plasma flow surrounding auroral arcs can benefit from auroral arc information provided by all‐sky imageryModeling realistic auroral current closure needs drivers that vary along‐arc, across‐arc, and in altitude via electron precipitation spectra [ABSTRACT FROM AUTHOR]

Pc5 ULF waves play an important role in transporting energy and particles in the coupled magnetospheric and ionospheric system. They are known to be initiated by dynamic pressure fluctuations upstream of the magnetopause, including those induced by hot flow anomalies (HFAs). However, the role of HFAs in generating magnetospheric and ground magnetic Pc5 ULF oscillations has not been investigated statistically yet. Thus, in this paper, we investigate the contribution of HFAs to ground magnetic Pc5 ULF oscillations and analyze how the characteristics of HFAs influence these oscillations, based on the coordinated observations between the THEMIS probes and the ground magnetometers at high latitudes during the years 2008, 2009 and 2019. We find that HFAs can serve as a notable source of ground magnetic Pc5 ULF oscillations, with about 18.9% of Interplanetary Magnetic Field (IMF) discontinuity‐induced HFAs associated with discernible enhancements in Pc5 ULF wave power, whereas spontaneous HFAs play a comparatively minor role in generating these oscillations. Furthermore, we observe that the cores of HFAs are likely to contribute more significantly to modulating the induced ground magnetic Pc5 ULF oscillations than their compressed boundaries. More dynamic pressure reductions within HFA cores correspond to stronger ground magnetic Pc5 ULF oscillations. Additionally, HFAs can propagate with the IMF discontinuity along the bow shock, continuously generating ground magnetic Pc5 ULF oscillations during their propagation. This research sheds light on the mechanisms underlying Pc5 ULF wave generation and underscores the role of HFAs in driving magnetospheric‐ionospheric interactions. Plain Language Summary: Ultra Low Frequency (ULF) waves, specifically Pc5 waves, are important for transporting energy and particles between the Earth's magnetic field and its upper atmosphere. These oscillations start because of changes in pressure outside the Earth's magnetosphere, such as hot flow anomalies (HFAs). However, it has not been studied how HFAs contribute to ground Pc5 oscillations in detail yet. So, in this paper, we look at how HFAs make Pc5 oscillations in the Earth's geomagnetic field and how the features of HFAs affect these oscillations. We studied data from THEMIS probes and ground magnetometers in 2008, 2009, and 2019. We found that about 18.9% of triggered HFAs caused noticeable increases in ground magnetic Pc5 wave power. Spontaneous HFAs didn't have as big of an effect. We also found that the core of HFAs is more important for making Pc5 waves than the edges. When the pressure reduction inside HFAs increases, Pc5 waves get stronger. Also, we noticed that HFAs move together with discontinuities in the solar wind, creating Pc5 oscillations as they move. This research helps us understand how Pc5 oscillations are made and shows that HFAs are important for connecting different parts of Earth's space environment. Key Points: HFAs can be an external source of ground magnetic Pc5 ULF oscillations, while SHFAs have weaker effects on generating these oscillationsThe cores of HFAs contribute more to modulating their induced intensity of ground magnetic Pc5 ULF oscillations than their boundariesHFA‐induced ground magnetic Pc5 ULF oscillations can propagate following the propagation direction of HFAs [ABSTRACT FROM AUTHOR]

Statistically ion and electron densities are enhanced above strong crustal magnetic field regions according to measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. Plasma created by ionization of neutrals in the lower ionosphere (where chemistry dominates) flows upward and becomes trapped on closed magnetic field loops. Enhanced ion density in the ionosphere (particularly O2+) is associated with enhanced photochemical escape of atomic oxygen. This paper presents a quasi‐1D multi‐fluid time‐dependent model of the Martian ionosphere for nine ion species. Ionospheric temperatures are adopted but ion densities and velocities (along the field lines) are determined using a numerical solution of the continuity and momentum equations. Diurnal effects are explored by varying photoionization rates. Three crustal field cases are considered: a low altitude closed, a high altitude closed, and a high altitude open field line. Additionally, a case with no crustal field is modeled to provide a comparison between regions with and without crustal fields in the upper Martian ionosphere. Model results show higher ion and electron densities in the crustal field cases than in the purely induced field case. Additionally, we find that densities are generally higher on the closed field lines than on the open field lines, and ion velocities are generally up the field lines, away from the Martian surface. We also find that velocities are larger on the open field line case. We compare modeled density results to MAVEN data and find general agreement. Implications for atmospheric escape, particularly photochemical escape of O, are also discussed. Plain Language Summary: Mars may not have a global magnetic field like the Earth, but it does have magnetic sources in its crust, giving rise to localized crustal magnetic fields. Previous spacecraft missions have measured increased ion and electron densities over regions where these crustal fields are strongest. This paper presents a model of ion flow along crustal fields at Mars, to try to explain the enhancement seen in data. Ion densities and velocities along crustal field lines are calculated. A diurnal (day to night) cycle is implemented to see how densities and velocities change throughout a Mars day. Multiple crustal field cases are modeled, as well as a generic "non‐crustal" ionosphere case. Modeled results show higher ion and electron densities in the crustal field line cases when compared to the non‐crustal case. Differences between modeled cases are compared with data results, and general agreement is evident. The effects of the modeled crustal fields on atmospheric escape are also discussed. Key Points: Plasma flows along Martian crustal magnetic field lines are modeled for nine ion speciesPlasma densities are higher for closed crustal magnetic fields than for open or induced fieldsUpward ion flow speeds are greater on open than on closed crustal magnetic fields [ABSTRACT FROM AUTHOR]

Ionospheric delay, as one of the largest error sources in radio propagation, can only be corrected for this error using the ionospheric delay correction model for Global Navigation Satellite System (GNSS) single‐frequency users. In this paper, the 2021 geomagnetic storm event is selected, and based on the measured ionospheric data from the GNSS observatory, the perturbation of the ionosphere by the geomagnetic storm event is analyzed, and it is found that the response of the ionosphere to the geomagnetic storm has obvious differences in the response characteristics and response time in different latitude regions. The performance of the global ionospheric map (GIM), the empirical model, and the broadcast ionospheric model during the geomagnetic storm‐induced ionospheric perturbation is analyzed and the change in the accuracy of each ionospheric model during the geomagnetic storm‐induced ionospheric perturbation is investigated, using the measured electron content of the GNSS as a benchmark. The results show that there is good agreement between the GIM products and the measured electron content during the period of ionospheric calm and the period of ionospheric perturbation. It is worth noting that geomagnetic storms do not necessarily lead to a decrease in the accuracy of ionospheric delay‐correction models, and in some cases, the models that were originally under‐accurate show a tendency to improve their accuracy during the period of perturbation instead. Neither the broadcast ionospheric model nor the electron content of the empirical model output responds to geomagnetic storm‐induced ionospheric perturbations. Plain Language Summary: The change characteristics of the ionosphere during geomagnetic storms are very complex. In this paper, we study the characteristics of ionospheric changes during geomagnetic storms and the performance of models during ionospheric perturbations. The results show that the ionospheric characteristics at different latitudes during geomagnetic storms are very different; and there is a phenomenon that the accuracy of the model correction is improved during the perturbation of geomagnetic storms. This paper provides a reference for improving the performance enhancement and application of ionospheric delay correction models. Key Points: Ionospheric disturbances caused by geomagnetic storms have different spatial and temporal characteristicsGlobal ionospheric map has the optimal performance in the calm period and the perturbation periodThe broadcast ionospheric model and the empirical model do not respond to ionospheric perturbations [ABSTRACT FROM AUTHOR]

Ultra‐low frequency (ULF) waves transfer energy and momentum into the ionosphere‐thermosphere system. To quantify this energy, this paper first presents a new method to quantitatively detect ULF waves in Incoherent Scatter Radar (ISR) data based on 2D fast‐Fourier transforms and subsequent reconstruction of the wave. In parallel with other data sets, including optical, magnetometer, satellite, and models, we present the first full ionospheric energy dissipation rates for a ULF wave, split into electromagnetic (EM) and kinetic fluxes. The EM energy deposition is calculated from the use of the Poynting theorem, looking at Joule and frictional heating rates, where both rates show the same order of magnitude (1.24 × 1013 and 7.3 × 1012 J) respectively when integrated over the wave lifetime of 2 hr 15 min and an area of 4° magnetic latitude × 74° magnetic longitude. However, contrary to the common assumption that the EM flux is dominant, we determined the kinetic flux, to be almost equal in magnitude (8.7 × 1012 J). This indicates that previous papers might have underestimated the total energy dissipation by ULF waves. Compared to the substorm energy budget, we find that locally, the ULF wave event studied here makes up approximately 10% of a typical substorm cycle budget. Plain Language Summary: The Earth's magnetic field lines can move back and forth regularly, like waves on a guitar string. When this happens on the time scale of minutes, we call these ultra‐low frequency (ULF) waves. ULF waves play an important role in the transfer of energy from the Earth's magnetic field to the Earth's upper atmosphere. In this study, we developed a new method to detect ULF waves in radar data to obtain information about the wave. By combining several data sets, such as radar, optical, satellite, and magnetic field measurements, we were then able to determine how much energy is being transferred in one ULF wave event. Both electromagnetic and kinetic energy are important in this transfer of energy. Key Points: We present a new method to detect and reconstruct ULF waves in ISR data with a 2D fast‐Fourier transformWe estimate ionospheric energy dissipation rates due to EM and kinetic energy sources using the new methodWe find that kinetic and EM energy rates are of similar magnitude and should both be included in ionospheric energy deposition by ULF waves [ABSTRACT FROM AUTHOR]

Enhanced interaction between solar‐wind and Earth's magnetosphere can cause space weather and geomagnetic storms that have the potential to damage critical technologies, such as magnetic navigation, radio communications, and power grids. The severity of a geomagnetic storm is measured using the disturbance‐storm‐time (Dst) index. The Dst index is calculated by averaging the horizontal component of the magnetic field observed at four near‐equatorial observatories and is used to drive geomagnetic disturbance models. As a key specification of the magnetospheric dynamics, the Dst index is used to drive geomagnetic disturbance models such as the High Definition Geomagnetic Model—Real Time. Since 1975, forecasting models have been proposed to forecast Dst solely from solar wind observations at the Lagrangian‐1 position. However, while the recent Machine‐Learning (ML) models generally perform better than other approaches, many are unsuitable for operational use. Recent exponential growth in data‐science research and the democratization of ML tools have opened up the possibility of crowd‐sourcing specific problem‐solving tasks with clear constraints and evaluation metrics. To this end, National Oceanic and Atmospheric Administration (NOAA)'s National Centers for Environmental Information and the University of Colorado's Cooperative Institute for Research in Environmental Sciences conducted an open data‐science challenge called "MagNet: Model the Geomagnetic Field." The challenge attracted 622 participants, resulting in 1,197 model submissions that used various ML approaches. The top models that met the evaluation criteria are operationally viable and retrainable and suitable for NOAA's operational needs. The paper summarizes the competition results and lessons learned. Plain Language Summary: Solar wind interacting with Earth's magnetosphere can cause geomagnetic storms, damaging critical technologies. The disturbance‐storm‐time (Dst) index measures storm severity, driving geomagnetic disturbance models. Traditional Dst forecasting relied on solar wind observations, but recent Machine Learning (ML) models show promise. However, many are unsuitable for operational use. To explore viable ML solutions, National Oceanic and Atmospheric Administration and the University of Colorado organized the "MagNet: Model the Geomagnetic Field" challenge. Six hundred and twenty‐two participants submitted 1,197 ML‐based models for predicting Dst. The top‐performing models meeting evaluation criteria are operationally viable and retrainable, meeting NOAA's operational needs. The paper summarizes competition results and insights, emphasizing ML's potential to enhance geomagnetic storm forecasting for practical applications. Key Points: The MagNet challenge attracted 622 participants from 64 countries who submitted 1,197 models to predict Dst in a real‐time modeling environmentThe ensemble average of the top four winning models, which used different modeling architectures, performed better than individual models for both competition and post‐competition dataThe challenge revealed notable successes and areas for improvement [ABSTRACT FROM AUTHOR]

GOES‐16 and GOES‐17 are the first of NOAA's Geostationary Operational Environmental Satellite (GOES)‐R series of satellites. Each GOES‐R satellite has a magnetometer mounted on the end (outboard) and one part‐way down a long boom (inboard). This paper demonstrates the relative accuracy and stability of the measurements on a daily and long‐term basis. The GOES‐16 and GOES‐17 magnetic field observations from 2017 to 2020 have been compared to simultaneous magnetic field observations from each other and from the previous GOES‐NOP series satellites (GOES‐13, GOES‐14 and GOES‐15). These comparisons provide assessments of relative accuracy and stability. We use a field model to facilitate the inter‐satellite comparisons at different longitudes. GOES‐16 inboard and outboard magnetometers data suffer daily variations which cannot be explained by natural phenomena. Long‐term‐averaged GOES‐16 outboard (OB) data has daily variations of ±3 nT from average values with one‐sigma uncertainty of ±1.5 nT. Long‐term averaged GOES‐17OB magnetometer data have minimal daily variations. Daily average of the difference between the GOES‐16 outboard or GOES‐17 outboard measurements and the measurements made by another GOES satellite are computed. The long‐term averaged results show the GOES‐16OB and GOES‐17OB measurements have long‐term stability (±2 nT or less) and match measurements from magnetometers on other GOES within limits stated herein. The GOES‐17OB operational offset (zero field value) was refined using the GOES‐17 satellite rotated 180° about the Earth pointing axis (known as a yaw flip). Plain Language Summary: GOES‐16 and GOES‐17 are the first two of the R‐series of the NOAA's Geostationary Operational Environmental Satellite (GOES). Like previous GOES satellites, they carry two magnetometers (inboard and outboard on a long boom) to measure the magnetic field at geosynchronous orbit (an altitude of approximately 35,786 km above mean sea level). Because these data are used to provide users of space‐based assets with the knowledge of the space environment and to provide input for research, the accuracy and stability of the new data sets relative to previous data sets are important. There are known variations in the data from the station‐keeping thrusters which are removed from the data studied. Previous studies showed that the GOES‐16 measurements contain artificial diurnal variations. This study shows that the diurnal variations of the outboard magnetometer data are useful and within specified limits. The GOES‐17 measurements do not have significant daily variations. Based on simultaneous measurements from the other GOES satellites, GOES‐16 and GOES‐17 outboard data are stable over a period of years. Key Points: GOES‐16 magnetic field data have artificial diurnal variations which are larger than in other GOES satellites and which change with seasonDaily averages of corrected magnetic field of GOES‐16/17 match simultaneous data from GOES‐13/14/15 nT except for eastward componentThe corrected GOES‐17 data match the GOES‐18 data when GOES‐17 and GOES‐18 are separated by 0.2° of longitude [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 H2020 SafeSpace project aims at the implementation of a space weather safety prototype, in particular to predict the deep charging hazard. The proposed service is built on a Sun‐to‐Earth chain of physical codes that propagates physical information and uncertainties in order to model the outer radiation belt dynamics. In this paper, we present the inner magnetosphere section of the SafeSpace pipeline that relies on solar wind driven and hourly updated models that describe the trapped electron environment (VLF waves, cold plasma and seed population densities), as well as the physical processes to which the trapped electrons are subjected to, such as radial diffusion and wave particle interactions. Then, this physical configuration is poured into the Salammbô‐EnKF model, a data assimilation radiation belt model which provides a global forecast of the densities across the radiation belts. We have compared the forecasting performance of this new modeling pipeline to a reference model during the St. Patrick's Day storm in 2015. We show that the new SafeSpace implementation shows closer results to the observations in addition to a better forecast within the prediction horizon. Plain Language Summary: The Sun is an active star at the origin of several charged particle emissions. Some of these particles interact with the Earth's magnetic field and contribute in dynamically populating the so‐called radiation belts. The radiation belts are a region in the near‐Earth space where high energy charged particles can remain trapped, which endangers spacecraft orbiting around the planet. In order to warn spacecraft operators of probable incoming events, the SafeSpace project aims at forecasting the dynamics of the electron radiation belts from their origin at the Sun. To do so, we introduce a framework where several physical models from the Sun to the Earth are chained and interlinked. Our approach also relies on assimilating data from satellites orbiting in the radiation belts. In this paper, we describe improvements implemented to some of the models at one end of the SafeSpace modeling chain, which simulate the processes taking place within the Earth's inner magnetosphere. In particular, we show that these developments contribute to improving the 2‐to‐4 days ahead forecasts of electron fluxes in the radiation belts compared to a pre‐existing reference model during the "St. Patrick's Day" storm in March 2015. Key Points: The SafeSpace project strives to improve the nowcast and forecast of the outer electron radiation belt dynamicsThe prototype relies on a pipeline of physical codes, propagating information and uncertainties from the Sun to the EarthThis new solar wind driven implementation, coupled to data assimilation shows improved forecast capabilities compared to a reference model [ABSTRACT FROM AUTHOR]

Rapid increases in solar wind dynamic pressure, known as solar wind pressure pulses, compress the Earth's magnetosphere and can rapidly restructure the electrodynamics within. The propagation of pressure pulse effects into the magnetosphere is known as a geomagnetic sudden commencement (SC). SCs can be further subdivided into compressions which are rapidly followed by a geomagnetic storm (a sudden storm commencement, SSC) and those which are not (a sudden impulse, SI). In this paper, SSCs and SIs are compared and contrasted, and we examine in particular the differences between the pressure pulses that drive SSCs/SIs, and explore the physical conditions of the magnetosphere before pressure pulse arrival. Firstly, it is shown that SSCs are more likely to be driven by pressure pulses with higher magnitude and/or shorter rise time. Secondly, the magnetosphere is primed by stronger driving conditions and higher geomagnetic activity prior to SSCs than SIs. Finally, there is a solar cycle dependence in the occurrence and magnitude of solar wind pressure pulses. Plain Language Summary: The solar wind's dynamic pressure controls the size of the cavity the Earth's magnetic field forms in space. When the pressure increases rapidly, this is known as a solar wind pressure pulse. Pressure pulses can affect currents and magnetic fields within the Earth's space environment, and can have serious space weather implications. In this paper, the differences between pressure pulses that are followed by geomagnetic storms (large releases of energy in the Earth's system), and those that are not are investigated. The state of the Earth's system before the arrival of the pressure pulse is also considered, and its contribution to the resulting space weather effects. It is shown that larger pressure pulses are more likely to trigger a geomagnetic storm. Additionally, analysis presented shows that the Earth's system may already be active prior to the triggering of these storms. Finally, the occurrence and strength of pressure pulse events follows solar activity. Key Points: There is a solar cycle dependence to the occurrence and magnitude of sudden commencements (SCs)Sudden storm commencements (SSCs) are driven by higher magnitude and/or shorter duration pressure pulsesThe magnetosphere is primed by stronger solar wind/interplanetary magnetic field and higher geomagnetic activity for SSCs [ABSTRACT FROM AUTHOR]

This paper investigates the midlatitude ionospheric disturbances over the American/Atlantic longitude sector during an intense geomagnetic storm on 23 April 2023. The study utilized a combination of ground‐based observations (Global Navigation Satellite System total electron content and ionosonde) along with measurements from multiple satellite missions (GOLD, Swarm, Defense Meteorological Satellite Program, and TIMED/GUVI) to analyze storm‐time electrodynamics and neutral dynamics. We found that the storm main phase was characterized by distinct midlatitude ionospheric density gradient structures as follows: (a) In the European‐Atlantic longitude sector, a significant midlatitude bubble‐like ionospheric super‐depletion structure (BLISS) was observed after sunset. This BLISS appeared as a low‐density channel extending poleward/westward and reached ∼40° geomagnetic latitude, corresponding to an APEX height of ∼5,000 km. (b) Coincident with the BLISS, a dynamic storm‐enhanced density plume rapidly formed and decayed at local afternoon in the North American sector, with the plume intensity being doubled and halved in just a few hours. (c) The simultaneous occurrence of these strong yet opposite midlatitude gradient structures could be mainly attributed to common key drivers of prompt penetration electric fields and subauroral polarization stream electric fields. This shed light on the important role of storm‐time electrodynamic processes in shaping global ionospheric disturbances. Plain Language Summary: The storm‐time midlatitude ionosphere is a highly dynamic region that can exhibit much more pronounced electron density gradients and disturbances than expected. The combined data from ground‐based and satellite measurements provided valuable insights into the intricate behavior of the midlatitude ionosphere during an intense geomagnetic storm on 23 April 2023. The midlatitude ionosphere was characterized by significant electron density gradient structures, comprising both phenomenal density depletion and exceptional enhancements. Notably, a remarkable band‐like ionospheric super‐depletion structure was observed in local dusk, which extended to ∼40° geomagnetic latitude, corresponding to an altitude of ∼5,000 km above the geomagnetic equator. In contrast, a significant midlatitude ionospheric density enhancement plume appeared simultaneously in local afternoon, which exhibited a dynamic variation with its intensity being quickly doubled and halved in just a few hours. The synchronous occurrence of these striking yet opposing density gradients highlights the importance of electrodynamic effect driven by common key drivers of storm‐time perturbed electric fields. This underscores the complex and interconnected nature of the ionospheric response during intense geomagnetic storms. Key Points: The storm main phase was characterized by coincident nightside bubble‐like ionospheric super‐depletion structure (BLISS) and dayside storm‐enhanced density (SED)The BLISS manifested as a poleward/westward‐streaming channel and extended to ∼40 MLAT, corresponding to an APEX height of ∼5,000 kmThe SED plume experienced a dynamic variation with the plume intensity being quickly doubled and halved in just a few hours [ABSTRACT FROM AUTHOR]

Auroral particle precipitation is usually assumed to be equally strong for both signs of the By component of the interplanetary magnetic field (IMF). This is also the case in most currently used precipitation models, which parameterize solar wind driving by empirical coupling functions. However, recent studies have showed that geomagnetic activity is significantly modulated by the signs and amplitudes of IMF By and the Earth's dipole tilt angle Ψ. This so called explicit By dependence is not yet included in any current precipitation models. In this paper, we quantify this By dependence for auroral electron precipitation for the first time. We use precipitation measurements of the Defense Meteorological Satellite Program (DMSP) Special Sensor J instruments from years 1995–2022. We show that the dawnside electron precipitation at energies 13.9–30 keV is greater at auroral latitudes for opposite signs of By and Ψ in both hemispheres, while the dusk sector is mostly unaffected by By and Ψ. For energies below 6.5 keV the By dependence is strong poleward of the auroral oval in the summer hemisphere, also exhibiting a strong dawn‐dusk asymmetry. We also show that By dependence of precipitation modulates ionospheric conductance. Plain Language Summary: Electron precipitation into the Earth's ionosphere creating the aurora borealis is driven by the magnetic field carried by the solar wind. The electron precipitation is known to increase the most, when the magnetic field of the solar wind points to south. The currently used models assume equally strong electron precipitation for eastward and westward solar wind magnetic fields. However, in this paper we show that the electron precipitation is different for duskward and dawnward magnetic fields, and that this magnetic field dependence varies with the season. We show that the electron precipitation is stronger on the dawnside in both hemispheres during the northern hemisphere winter when the solar wind magnetic field points duskward. In northern hemisphere summer the dependence on the magnetic field direction is opposite. We show that the solar wind magnetic field modulates the ionospheric conductivity in a similar way. Key Points: IMF By and Earth's dipole tilt angle Ψ (season) modulate auroral electron precipitationPrecipitation is stronger for 13.9–30 keV at auroral latitudes on the dawnside for both hemispheres, when By and Ψ have opposite signsBy drives a strong dawn‐dusk difference for energies 1.4–6.5 keV in the summer hemisphere [ABSTRACT FROM AUTHOR]

In this study, we present ionospheric observations of field‐aligned currents from AMPERE and the ESA Swarm A satellite, in conjunction with high‐resolution thermospheric density measurements from accelerometers on board Swarm C and GRACE‐FO, for the third and 4 February 2022 geomagnetic storms that led to the loss of 38 Starlink internet satellites. We study the global storm time response of the thermospheric density enhancements, including their decay and latitudinal distribution. We find that the thermospheric density enhances globally in response to high‐latitude energy input from the magnetosphere‐solar wind system and takes at least a full day to recover to pre‐storm density levels. We also find that the greatest density perturbations occur at polar latitudes consistent with the magnetosphere‐ionosphere dayside cusp, and that there appeared to be a saturation of the thermospheric density during the geomagnetic storm on the fourth. Our results highlight the critical importance of high‐latitude ionospheric observations when diagnosing potentially hazardous conditions for low‐Earth‐orbit satellites. Plain Language Summary: Upwards of a 100 km altitude lies the boundary between Earth's atmosphere and space, where the density of air exponentially decreases and many satellites constellations orbit. One of these constellations is Starlink, which provides satellite internet to customers on Earth. In February 2022, a pair of geomagnetic storms stuck Earth shortly after the launch of 49 Starlink satellites, heating the upper atmosphere and causing its density to drastically increase. The higher air density at the initial staging altitude of Starlink caused fatal drag conditions for 38 of the spacecraft, resulting in their destruction a few days later. This paper examines how the air density of the upper atmosphere changed globally in response to space weather energy being deposited at high latitudes during the Starlink geomagnetic storms of February 2022. Key Points: Ionospheric field‐aligned current and thermospheric neutral densities are examined for the 2022 Starlink geomagnetic stormsThe field‐aligned currents changed quickly, whilst the density decayed slowly and with differing timescalesAsymmetric latitudinal density distributions are consistent with asymmetries in the field aligned currents [ABSTRACT FROM AUTHOR]

Space weather can have major impacts on electrical infrastructure. Multiple instances of transformer damage have been attributed to geomagnetic storms in recent decades, for example, the Hydro Quebec incident of 1989 and the November 2001 storm in New Zealand. While many studies exist on the impacts of geomagnetic storms on power transformers in New Zealand, no studies exist that employ Dissolved Gas Analysis (DGA) techniques to relate geomagnetic storms to transformer gassing. A relationship has been reported between geomagnetic activity and DGA for South Africa, while none was found in a recent study in Great Britain. This paper attempts to examine this research question by examining dissolved gas data across eight power transformers in different substations in New Zealand from 2016 to 2019. Case studies were conducted which analyzed the DGA readings of each transformer alongside horizontal magnetic field component rate of change measurements at Eyrewell across six geomagnetic storms. These case studies were then augmented with an analysis of the entire data set where magnetic field measurements were compared with individual gas rates to establish a correlation between gas production and geomagnetic activity. Analysis of the results of this study concluded that no link had been found between the production of combustible gasses in a transformer and geomagnetic activity during the observation period. However, we note our dissolved gas analysis was largely in a geomagnetically quieter period, which may limit our analysis. The production of combustible gasses is not correlated to geomagnetic storms for the time period and transformers analyzed. Plain Language Summary: Space weather (changes in the Earth's magnetic field due to changes in the suns atmosphere) is well known to have major impacts on electrical infrastructure. Multiple incidents have been observed over recent decades which have been directly linked to space weather events, for example, the Hydro Quebec incident of 1989 and the November 2001 storm in New Zealand. In this study the impacts of space weather on power station transformers in New Zealand was analyzed. Data on transformer health for eight different transformers was compared to magnetic field activity from 2016 to 2019 to look for evidence of transformer damage due to solar storms. Case studies were analyzed across six different storms using dissolved gas analysis, which looks at the gas levels inside a transformer to determine its condition. Following the case studies general trends in the data were analyzed. From our analysis we concluded that no link had been found between space weather and transformer damage during the observation period. This was likely due to the quiet nature of the sun's atmosphere at the time. Key Points: Gas data from eight NZ transformers from 2016 to 2019 were analyzed to relate geomagnetic activity with the production of combustible gassesA statistical investigation was conducted analyzing gas records alongside magnetic field and current measurements over the same periodNo link found between combustible gas production in these transformers and geomagnetic activity for this time period [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]

Peak electron density data derived from GOLD measurements during 2018–2022 are used to analyze the magnitudes and correlations of ionospheric diurnal variability at low latitudes. The correlation distance describes the correlations between spatial locations and is defined in this paper as the angular separation at which the correlation coefficient decreases from 1 to 0.7. Variations in correlation distance with local time, season, magnetic latitude, solar activity, and geomagnetic activity are discussed in this study. The average value of the zonal correlation distance is approximately 8.55° and 3.56° for the meridional direction at low geomagnetic latitudes (magnetic latitudes <30°). The statistical results indicate that both zonal and meridional correlation distances vary little with local time premidnight, while they show pronounced seasonal and latitudinal variations. Both zonal and meridional correlation distances increase with increasing solar activity and decrease with enhancing geomagnetic activity. The EIA strength and gradient mainly modulate the distributions of correlation distances related to magnetic latitude, season, and solar flux level. An empirical model is constructed to describe the temporal and spatial variations in the correlation distance at low latitudes. The study of correlation distances would contribute to a better understanding of ionospheric variability and improvements in data assimilation. Plain Language Summary: The correlation distance is an important parameter in determining the background covariance matrix in data assimilations, which helps to transfer information from observations to the model‐driven background. The study of correlation distances can not only promote a better understanding of ionospheric variability but also improve ionospheric forecasts. More than 1,400 days of GOLD Nmax (peak electron density) data are applied for the statistical analysis of the correlation distance. In general, the correlation distance presents pronounced seasonal and latitudinal variations, varies little with local time premidnight, increases with increasing solar activity, and decreases with enhancing geomagnetic activity. The morphology of the EIA has a direct control on the correlation distance. The EIA strength and gradient mainly modulate the distributions of correlation distances related to magnetic latitude, season, and solar flux level. An empirical model is constructed, and it can effectively describe the temporal and spatial variations in the correlation distance at low latitudes. The results of correlation distances could further improve the accuracy of data assimilation. Key Points: EIA structures directly control the variation of correlation distancesHorizontal correlation distances increase with solar activity and vary with seasonAn empirical model is constructed to describe the variation in correlation distances with LT, mlat, season, solar and geomagnetic activities [ABSTRACT FROM AUTHOR]

The analytical theory is presented that describes the propagation of power lines emission (PLE) with frequency of 50/60 Hz in the heights range from the Earth surface to the magnetosphere. Validation of the theory is made by the comparison with earlier published results of numerical modeling. It is shown that the actual source of emission is a magnetic dipole formed by the power line current and by the secondary image current in the ground. The emission is propagating to the lower boundary of ionosphere, where its main part is reflected back, but some of the energy (a few percent) penetrates into the ionosphere. There it is transformed into a quasi‐flat whistler wave. The generation of current in ground and the reflection from the ionosphere are the main factors that reduce the emission into space. In the ionosphere wave fronts propagate approximately vertically, and the energy propagates in a certain direction that depends on the geomagnetic field inclination. Thus, the ionosphere acts as a focusing system that collects PLE into a unidirectional beam. The PLE intensity does not change with altitude within the total range of ionospheric heights. In the magnetosphere PLE is transformed to both magnetosonic and Alfvén waves and the emission splits into two rays: one propagates along the wave vector and the other one—along the geomagnetic field lines. A set of analytical solutions is presented allowing determining the change in PLE parameters with altitude depending on the source parameters and ionospheric conditions. Plain Language Summary: The Earth's electromagnetic environment is influenced by both natural and human activities. Currently, there is a noticeable increase in human‐induced activity in the near space, and its potential environmental effects are hard to predict. Among the various forms of electromagnetic waves in the extra‐low frequency range that travel from Earth into space, the most common is the emission from power lines operating at industrial frequencies of 50/60 Hz. Recently, satellites have been able to detect this emission, offering a promising opportunity for remotely observing and assessing the characteristics of terrestrial sources of electrical energy, including those that are hidden. This paper presents an analytical theory that describes the propagation of this emission from the Earth's surface to the magnetosphere. Initially, the emission behaves like a conventional radio wave, traveling through the neutral atmosphere at nearly the speed of light. However, as it ascends and undergoes multiple transformations in the ionosphere layers, it transitions into slow plasma waves of the magnetohydrodynamic nature. The paper provides a set of analytical solutions that enable the determination of emission parameters based on source characteristics and conditions along the wave's propagation path. Key Points: The analytical theory of the propagation of 50/60 Hz electromagnetic emission from the Earth surface to the magnetosphere is presentedAt ionospheric heights this emission turns into whistler‐wave, and then, in the magnetosphere, into magnetohydrodynamic wavesThe generation of image current in ground and the reflection from the bottom of the ionosphere are the factors that reduce energy emission to space [ABSTRACT FROM AUTHOR]

The critical frequency of ionospheric F2 layer (foF2) is an important ionospheric characteristic parameter. In this paper, a deep learning model based on Bidirectional long short‐term memory (BiLSTM) and attention mechanism is implemented for predicting the foF2 parameter. The inputs of models are the foF2 of globally available ionospheric ionosonde stations, geographic longitude and latitude, world time (UT), geomagnetic activity index, and solar activity index from 2015 to 2017. The superiority of the model is analyzed from different latitudes, seasons, and geomagnetic conditions. The results show that the prediction performance of the Bidirectional long short‐term memory model based on attention mechanism (BiLSTM‐Attention) is better than other models. The performance of the prediction model is optimal at high latitudes. The root mean square error (RMSE) and correlation coefficient (R) of the BiLSTM‐Attention model are 0.539 MHZ and 0.908 MHz at high latitudes, respectively. In terms of RMSE, it is 25.243%, 18.209%, and 11.203% lower than those of the international reference ionosphere (IRI), LSTM, and BiLSTM models, respectively. The prediction results of the four seasons show that the models are more applicable in winter. Compared with the IRI model, the RMSE of the BiLSTM‐Attention model in spring, summer, autumn, and winter is reduced by 24.344%, 21.181%, 25.058%, and 30.948%, respectively. The prediction effect of the BiLSTM‐Attention model is improved in the magnetic quiet period, the magnetic moderate period and the magnetic storm period. Also, the improvement effect is more obvious in the magnetostatic day, and the RMSE is reduced by 27.462% compared with the IRI model. Plain Language Summary: The critical frequency of ionospheric F2 layer (foF2) is an important parameter to characterize the variability of the ionosphere. In this study, we present an effective method to predict the foF2 based on ionosonde stations distributed around the world. The inputs to these models are the foF2 values, geographic longitude and latitude, world time (UT), geomagnetic activity index, and solar activity index from 2015 to 2017. Compared with the international reference ionosphere (IRI‐2016) model, long short‐term memory (LSTM) model, and Bidirectional long short‐term memory (BiLSTM) model, the Bidirectional long short‐term memory model based on attention mechanism (BiLSTM‐Attention) can achieve better performance under different latitudes, seasons and geomagnetic conditions. Key Points: The Bidirectional long short‐term memory (BiLSTM)‐Attention model is first used to predict the foF2 based on ionosonde stations distributed around the worldGeomagnetic activity index and solar activity index are added for the foF2 prediction of these modelsThe BiLSTM‐Attention prediction model shows better performance than the IRI‐2016, LSTM, and BiLSTM prediction models under different latitudes, seasons and geomagnetic conditions [ABSTRACT FROM AUTHOR]

Universal Time (UT) variations in many magnetospheric state indicators and indices have recently been reviewed by Lockwood and Milan (2023, https://doi.org/10.3389/fspas.2023.1139295). Key effects are introduced into magnetospheric dynamics by the eccentric nature of Earth's magnetic field, features that cannot be reproduced by a geocentric field model. This paper studies the UT variation in the occurrence of substorm onsets and uses a simple Monte‐Carlo model to show how it can arise for an eccentric field model from the effect of the diurnal motions of Earth's poles on the part of the geomagnetic tail where substorms are initiated. These motions are in any reference frame that has an X axis that points from the center of the Earth to the center of the Sun and are caused by Earth's rotation. The premise behind the model is shown to be valid using a super‐posed epoch study of the conditions leading up to onset. These studies also show the surprising degree of preconditioning ahead of the growth phase that is required, on average, for onset to occur. A key factor is the extent to which pole motions caused by Earth's rotation influence the near‐Earth tail at the relevant X coordinate. Numerical simulations by a global MHD model of the magnetosphere reveal the effect required to generate the observed UT variations and with right order of amplitude, albeit too small by a factor of about one third. Reasons why this discrepancy may have arisen for the simulations used are discussed. Plain Language Summary: Earth's magnetic field is eccentric in that the main magnetic (dipole) axis does not pass through the center of the Earth. This introduces a wobble into many aspect of near‐Earth space (the "magnetosphere") as Earth rotates. Many consequences of this have been noted in previous papers. This paper investigates the effect of the eccentricity on the phenomenon of magnetospheric substorms. It is shown that the explosive releases of energy stored in the tail of the magnetosphere are more likely to start ("onset") at some Universal Times (and therefore geographic longitudes) than others and an explanation of why is provided. Key Points: Universal Time (UT) effects in the magnetosphere are caused by the eccentric nature of Earth's intrinsic magnetic fieldThere is a UT dependence of the open flux (and hence also the integrated magnetopause reconnection voltage) needed to trigger substorm onsetGrowth phases that lead to substorm onset show considerable preconditioning by prior reconnection [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]

Directional drilling in the oil fields relies particularly on the "on‐fly" measurements of the natural magnetic field (measurements while drilling; MWD); the MWD are eventually used to construct the well path. These measurements are the superposition of the signals from the internal, core and crustal, and external, ionospheric and magnetospheric sources and the noise from magnetic elements in the borehole assembly. The internal signals are mostly constant in time and accounted for through the Earth's internal field models. The signals of external origin give rise to diurnal and irregular spatio‐temporal magnetic field variations observable in the MWD. One of the common ways to mitigate the effects of these variations in the MWD is to correct readings for the data from an adjacent land‐based magnetic observatory/site. This method assumes that the land‐based signals are similar to those at the seabed drilling site. In this paper, we show that the sea level and seabed horizontal magnetic fields differ significantly, reaching up to 30% of sea level values in many oceanic regions. We made this inference from the global forward modeling of the magnetic field using realistic models of conducting Earth and time‐varying sources. To perform such modeling, we elaborated a numerical approach to efficiently calculate the spatio‐temporal evolution of the magnetic field. Finally, we propose and validate a formalism allowing researchers to obtain trustworthy seabed signals using measurements at the adjacent land‐based site and exploiting the modeling results, thus without needing additional measurements at the seabed site. Plain Language Summary: Knowing the position of existing and new oil wells is vital for economic and safe sub‐horizontal drilling operations. A lower uncertainty in well positions allows for hitting smaller targets and avoiding the risk of well collisions. Determining the well position relies particularly on magnetic sensors installed close to the drill bit. For this, the models of spatially variable but constant in time magnetic field in the region of interest are routinely used. However, spatially and temporally varying space‐weather‐related geomagnetic field disturbances may affect the accuracy of the well position. One of the common ways to mitigate this problem is to correct magnetic field readings at a drill bit for the magnetic field measurements from an adjacent land‐based magnetic observatory. However, this method assumes that the land‐based signals are similar to those at the seabed drilling site. In this paper, we show that this is not the case, that is, the sea level and seabed magnetic fields differ significantly due to the electrical conductivity of the seawater column above the seabed site. Moreover, we propose and justify a numerical scheme which allows researchers to obtain trustworthy seabed signals by still using land‐based data but exploiting the results of dedicated modeling. Key Points: We present an approach to efficiently calculate the spatio‐temporal evolution of a magnetic field in a given conductivity model of the EarthWe show that sea level and seabed horizontal magnetic field differ significantlyWe propose and justify a formalism allowing us to calculate more accurately seabed magnetic field signals using adjacent land‐based data [ABSTRACT FROM AUTHOR]

The impacts of ionospheric irregularities on precise point positioning (PPP) have been commonly noticed in the field of the ionosphere and the precise application of the Global Navigation Satellite System. But few attentions have been paid to how ionospheric irregularities deteriorate the performance of PPP. Aiming at exploring the mechanism of degradation of PPP solutions during the period of ionospheric irregularities, this paper investigates the impacts of ionospheric irregularities on the performance of kinematic PPP. The experiment uses GPS observation data sampled at the 30‐s interval over China on the days of 2014, 2015, and 2017 covering some active space weather, for example, solar and geomagnetic activities. The results show that the ionospheric irregularities caused increased positioning errors (decimeter‐ to meter‐level), enlarged phase residuals (decimeter‐level), and increased the number of detected cycle slips in PPP processing in low latitude regions of China. By proposing a novel strategy that compares the number of detected cycle slips from 30 s‐sampling interval data and 1s‐sampling interval data at the same station in an "aligned" mode, we present direct evidence of the existence of the falsely detected cycle slips in 30 s‐sampling interval data by the traditional cycle‐slip detection threshold in PPP processing. We reveal that the unnecessary and frequent reinitialization of ambiguity induced by the falsely detected cycle slips is dominantly responsible for the degradation of kinematic PPP solutions during the period of ionospheric irregularities. Our findings pointed out the direction for the improvement of kinematic PPP performance in the environment of ionospheric irregularities. Plain Language Summary: Ionospheric irregularities are electron density irregularities within the ionosphere. Ionospheric irregularity is the main concern in the field of Global Navigation Satellite System (GNSS) due to its impacts on the precise application of GNSS. This paper investigates the impacts of ionospheric irregularities on precise point positioning (PPP) in the region of China. The results indicate that ionospheric irregularities caused decimeter‐level and meter‐level degradation of kinematic PPP in the low‐latitude region of China. Meanwhile, we reveal the mechanism of degradation of kinematic PPP induced by ionospheric irregularities. The falsely detected cycle slips induced by ionospheric irregularities are the dominant reason that causes degradation of kinematic PPP during the period of ionospheric irregularities. Our findings advanced the understanding of the mechanism of the impacts of ionospheric irregularities on kinematic PPP performance. Key Points: Kinematic precise point positioning (PPP) performances in the multi‐event condition of ionospheric irregularities over China are evaluatedThe ionospheric irregularities caused increased cycle slips and degraded PPP solutions in the south of China from sunset to midnightExtensive misjudged cycle slips are dominantly responsible for the degradation of PPP solution during the period of irregularities [ABSTRACT FROM AUTHOR]

Space weather induced Geomagnetically Induced Currents (GICs) that are hazardous to power networks at high latitudes are often the result of rapid changes in near‐Earth space current systems such as the auroral electrojets and field‐aligned currents. GIC activity at low‐middle latitudes may be driven by currents that are more relevant to these regions such as the ring or magnetopause current systems. Solar wind shocks create rapid changes in the magnetopause current that manifest as large step changes in the geomagnetic field at the Earth's surface, often referred to as geomagnetic sudden impulses (SIs), that are effective drivers of GIC activity in power networks at low‐middle latitudes. This paper describes the results of a study into the relationship between the driver of SIs, solar wind shocks, and their potential impact on power systems in the Australian region, as quantified by a GIC‐index. The initial data set for analysis was produced by programmatically scanning solar wind data obtained from the ACE satellite spanning the period 1998–2008 for solar wind shocks. For each identified solar wind shock, geomagnetic field data from the Australian region were analyzed to determine the corresponding SI and GIC‐index. Statistical analyses of GIC‐indices and various solar wind parameters associated with the shocks resulted in an empirical model that is a function of solar wind dynamic pressure, geomagnetic latitude, and change in solar wind speed with good operational predictive capability. This model was further assessed using online catalogs of solar wind shock events. Plain Language Summary: During energetic solar eruptions large clouds of charged particles and magnetic field from the sun's outer atmosphere, or corona, may be ejected into interplanetary space. These clouds are typically referred to as coronal mass ejections or CMEs and propagate in the continuous background stream of charged particles and magnetic field emanating from the sun referred to as the solar wind. CMEs may impact the Earth's magnetic field, compressing its outer boundary on the dayside and significantly enhancing current systems in the near‐Earth space environment. These currents generate electromagnetic fields that propagate to Earth and manifest as unwanted currents in power systems and long resource pipelines. This paper analyses the abrupt change in the Earth's magnetic field created during CME impact in terms of an index that quantifies the potential hazard to power systems, the Geomagnetically Induced Current (GIC)‐index, against the associated characteristic signatures of CMEs in solar wind data observed by satellites located upstream of the Earth toward the sun. A statistical analysis of solar wind data and GIC‐index data derived from magnetic field measurements over the Australian region is used to determine a forecast model that can provide warnings for the Australian power sector with sufficient lead time to implement mitigating actions. Key Points: Geomagnetic sudden impulses caused by solar wind shocks create Geomagnetically Induced Currents (GICs) that may be hazardous to power systems at low‐to‐middle latitudesStatistical analysis of solar wind shocks and GIC‐index data derived from magnetic field measurements over the Australian regionStatistical model is a function of solar wind dynamic pressure, speed, and geomagnetic latitude with good out‐of‐sample predictive power [ABSTRACT FROM AUTHOR]

This paper addresses one of the critical questions of scientific inquiry: How do we know when a given data set is representative of the phenomenon being examined? For paleomagnetists, the question is often whether a particular data set sufficiently averaged paleosecular variation (PSV). To this aim, we updated an existing PSV data set that now comprises 2,441 site mean directions from 94 individual studies (PSV10‐24). Minimal filtering for data quality resulted in 1,619 sites from 90 publications. Fitting PSV10‐24 with two newly defined parameters as well as two existing ones form the basis of a Giant Gaussian Process field model (THG24) consistent with the data. Drawing directions from THG24 yields directional distributions predicted for a given latitude allowing a comparison between empirical distributions and the cumulative distribution function generated by the model. This tests whether the observed data adequately averaged out PSV according to THG24. We applied these tests to five data sets from Large Igneous Provinces from the last billion years and find that they are consistent with the THG24 model as well. Sedimentary data sets that may have experienced inclination shallowing can be corrected using an (un)flattening factor that yields directions satisfying THG24 in a newly‐defined, four‐parameter space. This approach builds on the Elongation‐Inclination (E/I) method of Tauxe and Kent (2004), https://doi.org/10.1029/145gm08, so the approach introduced here is called SVEI. We show examples of the use of SVEI and explain how to use this newly developed Python code that is publicly available in the PmagPy GitHub repository. Plain Language Summary: Paleomagnetic vectors recorded by rocks and archeological materials yield information on the structure of the magnetic field through Earth's history. The geomagnetic field mostly resembles a geocentric dipole aligned with the spin axis, but the directions at any given time and place generally deviate from this simple model. Data sets produced over several decades help define global magnetic field behavior. Here, we updated a compilation of paleomagnetic data and used it to establish a new field model representative of the last 10 million years. Prior or emerging data sets can be tested against the model to see whether the two agree in terms of field structure and variability. We tested data sets as old as 1.1 billion years and found them compatible with the model. Moreover, this model can also assess, and potentially correct data from sedimentary rocks that may have suffered from inclination shallowing. Although other correction methods exist, our approach employs a more complete description of the geometry of directional data, thereby allowing a more quantitative comparison of empirical and predicted distributions. Corrected inclinations and their uncertainties define paleolatitudes more accurately, key for plate tectonic and paleoclimatic reconstructions. Key Points: Update of the paleosecular variation database from lava flows (PSV10‐24) for the last 10 MaDefinition of a new Giant Gaussian Process (GGP) model (THG24), compatible with PSV10‐24 matching VGP scatter including data sets as old as 1.1 GaDescription of the SVEI method (an update of E/I) to assess secular variation records and to correct for inclination shallowing in sediments [ABSTRACT FROM AUTHOR]

The paper presents the effects of the storm‐time prompt penetration electric fields (PPEF) and traveling atmospheric disturbances (TADs) on the total electron content (TEC), foF2 and hmF2 in the American sector (north and south) during the geomagnetic storm on 23–24 April 2023. The data show a poleward shift of the Equatorial Ionization Anomaly (EIA) crests to 18°N and 20°S in the evening of 23 April (attributed to eastward PPEF) and the EIA crests remaining almost in the same latitudes after the PPEF reversed westward. The thermospheric neutral wind velocity, foF2, hmF2, and TEC variations show that TADs from the northern and southern high latitudes propagating equatorward and crossing the equator after midnight on 23 April. The meridional keograms of ΔTEC show the TAD structures in the north/south propagated with phase velocity 470/485 m/s, wave length 4,095/4,016 km and period 2.42/2.30 hr, respectively. The interactions of the TADs also appear to modify the wind velocities in low latitudes. The eastward PPEF and equatorward TADs also favored the development of a clear/not so clear F3 layer in northern/southern regions of the equator. Plain Language Summary: The thermosphere‐ionosphere‐magnetosphere system is largely affected during events of geomagnetic storms. Its dynamics, mainly in the ionized environment, may impact modern lives by degradations in the satellite signals affecting, for example, all applications involving Global Navigation Satellite System. The thermosphere and ionosphere responses to the large geomagnetic storm of 23–24 April 2023 are analyzed here and the main discoveries are the unexpected spatial plasma density distribution over Boa Vista (MLat ≈ 8°N) due to resulting effects of a disturbed eastward electric field and traveling atmospheric disturbance (TAD). The interactions/interferences of TADs were able to explain the unexpected moment of the peak in thermospheric neutral wind speed measurements over the equatorial station, as well as all variations in ionospheric parameters (foF2, hmF2, and total electron content) recorded in pairs by seven Digisondes and GNSS receivers spread across Brazil. Key Points: Interactions of traveling atmospheric disturbances (TADs) cause unexpected thermospheric neutral wind speeds in the American equatorial and low‐latitude sectorsThe effects resulting from a disturbed electric field and TADs were able to produce anomalous electron density distribution at low latitudesThe variations in the ionospheric observational measurements recorded around 4 UT in Brazil on 24 April 2023 were explained by the passages of TADs [ABSTRACT FROM AUTHOR]

Quantification of energetic electron precipitation caused by wave‐particle interactions is fundamentally important to understand the cycle of particle energization and loss of the radiation belts. One important way to determine how well the wave‐particle interaction models predict losses through pitch‐angle scattering into the atmospheric loss cone is the direct comparison between the ionization altitude profiles expected in the atmosphere due to the precipitating fluxes and the ionization profiles actually measured with incoherent scatter radars. This paper reports such a comparison using a forward propagation of loss‐cone electron fluxes, calculated with the electron pitch angle diffusion model applied to Van Allen Probes measurements, coupled with the Boulder Electron Radiation to Ionization model, which propagates the fluxes into the atmosphere. The density profiles measured with the Poker Flat Incoherent Scatter Radar operating in modes especially designed to optimize measurements in the D‐region, show multiple instances of close quantitative agreement with predicted density profiles from precipitation of electrons caused by wave‐particle interactions in the inner magnetosphere, alternated with intervals with large differences between observations and predictions. Several‐minute long intervals of close prediction‐observation approximation in the 65–93 km altitude range indicate that the whistler wave‐electron interactions models are realistic and produce precipitation fluxes of electrons with energies between 10 keV and >100 keV that are consistent with observations. The alternation of close model‐data agreement and poor agreement intervals indicates that the regions causing energetic electron precipitation are highly spatially localized. Plain Language Summary: Establishing how electromagnetic waves in the magnetosphere push high‐energy electrons into a funnel directed toward Earth along magnetic field lines is a critically important step to predict how electrons are lost into the atmosphere during geomagnetic storms. Wave‐electron interaction models predict the number of electrons that are funneled toward Earth from a set of in‐situ spacecraft measurements. As the electrons hurl into the upper atmosphere, ionization models predict how many electrons would be released by the neutral atmosphere due to the bombardment from funneled electrons. Electron density measurements with a radar especially tuned to optimize detection of electron densities in the upper atmosphere can be compared to predicted electron densities to determine the validity of the electron loss models. This paper reports a comparison for an interval of time when a Van Allen Probes spacecraft is measuring the waves and electrons at a location that would guarantee that the electrons would fall near the radar's location in Poker Flat, Alaska. The comparison shows that the models considered predict the correct number of electrons in multiple instances, thus establishing an important step in verifying the validity of the models of electron loss during geomagnetic storms. Key Points: Comparison between observed and modeled density for electron precipitation due to wave‐particle interactions in the magnetosphereComparison verifies the validity of D‐region electron density predicted by pitch‐angle diffusion models of wave‐particle interactionObserved electron profiles are obtained with an incoherent scatter radar mode especially designed to optimize measurements in the D‐region [ABSTRACT FROM AUTHOR]

In this paper, we statistically investigate an artifact in Langmuir Probe (LP) observations of Swarm satellites. A small peak of electron density (Ne) is frequently found in the Swarm data around the dayside dip equator. On the contrary, they appear in neither the Total Electron Content data of the Swarm/Global Positioning System Receivers nor COSMIC‐2 in‐situ measurements at similar altitudes but with low orbit inclination. Arguably, this peak does not represent natural ionospheric irregularities but is likely to result from artifacts. The phenomena are found regardless of the season, solar activity, and the velocity direction of the satellite (ascending and descending). They predominantly occur when the magnetic declination is close to zero, that is, when the Swarm ram direction and the Earth's magnetic field are aligned under sunlight. Hence, we attribute the phenomenon to intensified secondary electrons escape when the geomagnetic field lines are normal to conducting surfaces that emit secondary electrons. Since the magnitude of the artifact is only a few percent of the large‐scale background, it does not have a serious impact on the value of the Swarm/LP data in scientific research. Nevertheless, future efforts to determine the exact cause of the artifacts will contribute to improving the reliability and quality of plasma density and temperature measured by Swarm/LP. Plain Language Summary: In this paper, we statistically investigate artifacts found in Langmuir Probe (LP) observations of Swarm satellites and search for their possible causes. LP is an instrument that measures the density and temperature of charged particles (so‐called "plasma") around the satellite. Unexpectedly, small peaks of plasma density often occur around the dayside dip equator in the Swarm/LP data, while they are not at all observed in other similar equipment, such as Swarm Global Positioning System Receivers or COSMIC‐2 satellites' ion probes at similar altitudes. For this reason, we deem this peak an artifact. This phenomenon occurs in all seasons, solar activity, and satellite movement directions. But, it predominantly appears when the ram direction of Swarm is nearly aligned with the Earth's magnetic field under sunlight. Hence, we consider that it originates from enhanced secondary electrons escape under a particular magnetic field configuration. The artifacts do not have a deleterious impact on scientific research because they are only a few percent of the background. However, efforts to determine the exact cause of artifacts are warranted for improving the reliability and quality of LP data. Key Points: Swarm encounters peaks of electron density at the dayside dip equator under zero magnetic declination, which is arguably an artifactThe artifacts occur for all seasons and solar activity, and for both ascending/descendingWe suggest that the artifacts are associated with enhanced secondary electrons escape under favorable magnetic field configurations [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]

Waves which couple to energetic electrons are particularly important in space weather, as they drive rapid changes in the topology and intensity of Earth's outer radiation belt during geomagnetic storms. This includes Ultra Low Frequency (ULF) waves that interact with electrons via radial diffusion which can lead to electron dropouts via outward transport and rapid electron acceleration via inward transport. In radiation belt simulations, the strength of this interaction is specified by ULF wave radial diffusion coefficients. In this paper we detail the development of new models of electric and magnetic radial diffusion coefficients derived from in‐situ observations of the azimuthal electric field and compressional magnetic field. The new models use L∗ ${L}^{\ast }$ as it accounts for adiabatic changes due to the dynamic magnetic field coupled with an optimized set of four components of solar wind and geomagnetic activity, Bz ${B}_{z}$, V $V$, Pdyn ${P}_{\mathrm{d}\mathrm{y}\mathrm{n}}$, and Sym−H $\mathrm{S}\mathrm{y}\mathrm{m}-H$, as independent variables (inputs). These independent variables are known drivers of ULF waves and offer the ability to calculate diffusion coefficients at a higher cadence then existing models based on Kp. We investigate the performance of the new models by characterizing the model residuals as a function of each independent variable and by comparing to existing radial diffusion models during a quiet geomagnetic period and through a geomagnetic storm. We find that the models developed here perform well under varying levels of activity and have a larger slope or steeper gradient as a function of L∗ ${L}^{\ast }$ as compared to existing models (higher diffusion at higher L∗ ${L}^{\ast }$ values). Plain Language Summary: The outer radiation belt is a region of space comprising highly energetic electrons. During periods of extreme space weather, the number and energy of these electrons can rapidly vary. During these periods as the electron energies and numbers become enhanced, they can pose a threat to satellite and space infrastructure. While we have an excellent understanding of the physical processes which drive radiation belt electron dynamics, we still have a limited ability to model and forecast radiation belt dynamics; this is a result of the complexity of Earth's radiation belt system. One of the key processes controlling radiation belt dynamics is Ultra Low Frequency (ULF) wave radial diffusion. In this work we detail the development a new model quantifying the strength of ULF wave radial diffusion in the outer radiation belt utilizing space base observations of the electric and magnetic fields in Earth's magnetosphere. Accurately quantifying ULF wave radial diffusion is fundamental to understanding radiation belt dynamics and any improvement or refinements in radial diffusion models can help to provide a better understanding of the complex radiation belt system and importantly improve hindcasts, nowcasts, and forecasts. Key Points: A new four‐component L*‐dependent radial diffusion modelThe new model uses L* accounting for adiabatic changes under varying levels of solar and geomagnetic activityA detailed parametric study identifies an optimized set of independent variables for the new radial diffusion models [ABSTRACT FROM AUTHOR]

On 12 May 2021 the interplanetary doppelgänger of the 9 May 2021 coronal mass ejection impacted the Earth's magnetosphere, giving rise to a strong geomagnetic storm. This paper discusses the evolution of the various events linking the solar activity to the Earth's ionosphere with special focus on the effects observed in the circumterrestrial environment. We investigate the propagation of the interplanetary coronal mass ejection and its interaction with the magnetosphere—ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analyzing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm was correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a net and rapid loss of relativistic electrons from the entire outer radiation belt. Our analysis shows no evidence for any short‐term recovery to pre‐storm levels during the days following the main phase. Storm effects also included a small Forbush decrease driven by the interplay between the interplanetary shock and subsequent magnetic cloud arrival. Plain Language Summary: On 12 May 2021 a coronal mass ejection (CME) emitted from the Sun on 9 May 2021 impacted the Earth, giving rise to a strong geomagnetic storm. This paper present a global view of the CME effects observed in the circumterrestrial environment focusing on its propagation and on its interaction with the magnetosphere—ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analyzing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm was correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a sudden loss of relativistic electrons from the entire outer radiation belt. Such kind of a global analysis is still the straightforward way available to understand the complex dynamics of the processes occurring in the circumterrestrial environment from a space weather point of view. Key Points: Global analysis of the 12 May 2021 geomagnetic stormInterplanetary coronal mass ejections propagation in the interplanetary spaceMagnetospheric‐ionospheric coupling analysis from both particle and field point of view [ABSTRACT FROM AUTHOR]

Ground‐based Global Navigation Satellite System (GNSS) receivers have become a ubiquitous tool for monitoring the ionosphere. Total electron content (TEC) data from globally distributed networks of ground‐based GNSS receivers are increasingly being used to characterize the ionosphere and its variability. The deployment of these GNSS receivers is currently limited to landmasses. This means that 7/10 of Earth's surface, which is covered by the oceans, is left unexplored for persistent ionospheric measurements. In this paper, we describe a new low‐power dual‐frequency Global Positioning System (GPS) receiver, called Remote Ionospheric Observatory (RIO), which is capable of operating from locations in the air, space, and the oceans as well as on land. Two RIO receivers were deployed and operated from the Tropical Atmosphere Ocean buoys in the Pacific Ocean, and the results are described in this paper. This is the first time that GPS receivers have been operated in open waters for an extended period. Data collected between 1 September 2018 and 31 December 2019 are shown. The observed TEC exhibits a clear seasonal dependence characterized by equinoctial maxima in the data at both locations. Both RIO receivers, deployed near the magnetic equator, show an 18–35% increase in TEC during moderately disturbed geomagnetic periods. Comparisons with the International Reference Ionosphere model show good agreement. The new capability presented in this paper addresses a critical gap in our ability to monitor the ionosphere from the 70% of the Earth's surface that is covered by water. Plain Language Summary: The upper levels of the atmosphere, from about 80 to over 1,000 km altitudes, collectively referred to as the ionosphere, consist of partially ionized gas. An increasingly large amount of ionospheric data comes from ground‐based receivers that passively benefit from the signals transmitted on board the Global Navigation Satellite System (GNSS) constellations. One of the most useful data sets provided by these GNSS receivers is the total electron content. Ground‐based GNSS receivers are widely deployed all over the world and have become the workhorse for doing ionospheric research. However, to date, the deployment of these GNSS receivers has been limited to landmasses, which leaves 70% of the Earth's surface covered by the oceans uninstrumented for ionospheric studies. In this paper, we describe a new low‐power dual‐frequency Global Positioning System receiver, called the Remote Ionospheric Observatory, which is capable of continuous operation from ocean buoys for extended periods. We present data from two Remote Ionospheric Observatory receivers deployed on buoys in the Pacific Ocean. The new capability described in this paper is anticipated to open up many new applications for passively monitoring the ionosphere from previously inaccessible regions, such as the ocean. Key Points: A new capability for measuring total electron content (TEC) from the ocean surface is presentedFirst measurements of TEC from two surface buoys in the Pacific Ocean are describedTEC enhancements in the equatorial region during moderate geomagnetic storms are observed [ABSTRACT FROM AUTHOR]

Exospheric temperature is one of the key parameters in constructing thermospheric models and has been extensively studied with in situ observations and remote sensing. The Global‐scale Observations of the Limb and Disk (GOLD) at a geosynchronous vantage point provides dayglow limb images for two longitude sectors, from which we can estimate the terrestrial exospheric temperature since 2018. In this paper, we investigate climatological behavior of the exospheric temperature measured by GOLD. The temperature has positive correlations with solar and geomagnetic activity and exhibits a morning‐afternoon asymmetry, both of which agree with previous studies. We have found that the arithmetic sum of F10.7 (solar) and Ap (geomagnetic) indices is highly correlated with the exospheric temperature, explaining ∼64% of the day‐to‐day variability. Furthermore, the exospheric temperature has good correlation with thermospheric parameters (e.g., neutral temperature, O2 density, and NO emission index) sampled at various heights above ∼130 km, in spite of the well‐known thermal gradient below ∼200 km. However, thermospheric temperature at altitudes around 100 km is not well correlated with the GOLD exospheric temperature. The result implies that effects other than thermospheric heating by solar Extreme Ultraviolet and geomagnetic activity take control below a threshold altitude that exists between ∼100 and ∼130 km. Plain Language Summary: In the terrestrial thermosphere, which is the topmost layer of the collisional atmosphere surrounding the Earth, temperature generally increases with altitude unlike in the troposphere near the surface. However, the thermospheric temperature does not increase indefinitely, but approaches an asymptote, which is referred to as the exospheric temperature, the temperature of the outermost layer of the atmosphere. The Global‐scale Observations of the Limb and Disk (GOLD) instrument, launched into a geosynchronous orbit in 2018, regularly observes atmospheric glow from the Earth's limb, from which we can estimate the terrestrial exospheric temperature (Texo). The GOLD Texo is higher in the afternoon than in the morning and generally increases as solar radiation strength or geomagnetic field variability increases. In this paper, we show that a simple arithmetic sum of the solar and geomagnetic indices can explain a large part of the day‐to‐day Texo variability. Also, Texo has good (poor) correlation with thermospheric parameters such as temperature and density above ∼130 km (at ∼100 km). The behavior suggests that factors other than solar radiation and geomagnetic energy deposition, both of which are correlated well with Texo, take control below a threshold altitude that is between ∼100 and ∼130 km. Key Points: We report on the climatology of exospheric temperature (Texo) measured by NASA‐GOLD in 2018–2021Texo is highly correlated with Ap and F10.7, whose linear combination can explain ∼64% of the Texo day‐to‐day variability in 2018–2021Texo has positive correlation with Swarm thermospheric mass density, GOLD disk temperature, GOLD O2 density, and TIMED/SABER TCI [ABSTRACT FROM AUTHOR]

In recent years, the evolution of the magnetic flux lobes in terms of location and intensity has been attributed to paleosecular variation of the geomagnetic field, reflecting outer‐core fluid convection close to the core‐mantle boundary. However, most results were based on observational data for the past 400 years supplemented by sparse archeomagnetic studies with data for approximately 3 kyr. In this paper, we construct a relative paleointensity (RPI) record and an inclination record spanning the past ∼90 kyr based on two cores from Tengchong Qinghai Lake (Yunnan Province, China), a closed crater lake that formed in the late Pleistocene. The evolution of flux lobes and the non‐dipole field can be assessed on a much longer time scale. Although the concentration and domain state of magnetic grains in the cores vary significantly, the RPI record is still representative of geomagnetic field features in the region of Yunnan Province, China. The contrasting trends in RPI with the records for eastern China since the late Holocene indicate the southeastward migration of the Siberian flux lobe. During the last glacial period, the RPI records of Tengchong Qinghai Lake and the North Atlantic Ocean show opposite trends, denoting the diverse and strong influence of the two flux lobe systems. The strong reverse flux lobe in the North Atlantic Ocean strengthened the non‐dipole field, while the weak normal flux lobe in Tengchong weakened the non‐dipole field. Plain Language Summary: Earth's magnetic field is composed of two main field components: a dipole field and a non‐dipole field. Although the non‐dipole field constitutes a minor component of the geomagnetic field, its variations in strength and location over different time scales have a significant influence on the surface expression of the geomagnetic field. The flux lobes arising from the fluid convection at the boundary between the core and mantle may produce the main components of the non‐dipole field. In recent years, the distribution of magnetic flux has been discussed based mainly on instrumental data and archeomagnetic data spanning a few kyr, which limits our understanding of flux lobe evolution on a much longer time scale. In this paper, we reconstruct a relative paleointensity (RPI) and an inclination records over the past ∼90 kyr from sediments of a closed volcanic lake in Tengchong, Yunnan Province, China. The results show that the RPI in the Tengchong area differs from the records for eastern China in the Holocene and from the records in the North Atlantic Ocean during the last glacial period. We conclude that a flux lobe may have played an important role in the non‐dipole field in the Tengchong and in the North Atlantic Ocean. Key Points: High‐resolution paleosecular variation records, including relative paleointensity (RPI) and inclination for the past 90 kyr, are derived from sediments in a closed lake in ChinaThe Holocene RPI trend obtained differs from records from records from eastern China, indicating the movement and intensification of the Siberian flux lobeThe opposing RPI patterns from the lake and the North Atlantic Ocean during the last glacial period indicate the influence of flux lobe systems on the non‐dipole field [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]

The ionospheric electron density is expected to enhance after sunrise during geomagnetic quiet days. In this paper, we report an anomalous large‐scale ionospheric TEC depletion structure occurring in morning hours over low latitudes in China under relatively quiet geomagnetic conditions. The depletion structure, which occurred over a wide longitude range of >35°, developed toward higher latitudes at the speed of ∼250 m/s. A statistical analysis using the data in 2018–2020 showed that such large‐scale daytime TEC depletion mainly occurred in summer (mostly with Kp < 3), with large intensities at ∼16–30°N. The geomagnetic ΔH measurements at the stations near and away from the magnetic dip equator showed positive values, which rules out the possible contribution from a westward electric field. Observations from multiple ionosondes revealed a net downward plasma transport during the TEC depletion. An enhanced poleward neutral wind during the early morning hours, which may induce downward plasma transport, was surmised to play a leading role in driving the large‐scale morning TEC depletion. Plain Language Summary: Under geomagnetic storms, the daytime ionosphere may undergo significant plasma density depletion over wide longitude and latitude regions. Possible driving mechanisms of large‐scale plasma density depletion include the suppression of the fountain effect by westward equatorial electrojets, the upward plasma diffusion caused by increasing electron temperature, and the decreased O/N2 ratio transported by perturbed neutral circulation. In this paper, we report cases of anomalous large‐scale plasma density depletion structures in morning hours of geomagnetic quiet days over low latitudes in China. The large‐scale plasma density depletion structure, which produced TEC reduction of ∼4 TECu, covered >3,500 km in the east‐west direction and developed poleward. Based on the observations from multiple ionosondes and magnetometers at equatorial and low latitudes, it is unlikely that the possible driving sources are from geomagnetic activities. We surmise that there could be an enhanced poleward neutral wind over a wide longitude region which induced downward plasma transport and produced the depletion structure. Key Points: A daytime large‐scale TEC depletion structure covering ∼35° in longitude under relatively quiet geomagnetic conditions was reportedThe daytime large‐scale depletion structure with poleward development mainly occurred in summer with large intensities at 16–30°NIt is surmised that enhanced poleward neutral wind could be a possible driver for the daytime large‐scale depletion structure [ABSTRACT FROM AUTHOR]

The minerals carrying the magnetic remanence in geological samples are commonly a solid solution series of iron‐titanium spinels known as titanomagnetites. Despite the range of possible compositions within this series, micromagnetic studies that characterize the magnetic domain structures present in these minerals have typically focused on magnetite. No studies systematically comparing the domain‐states present in titanomagnetites have been undertaken since the discovery of the single vortex (SV) structure and the advent of modern micromagnetism. The magnetic properties of the titanomagnetite series are known to vary strongly with composition, which may influence the domain states present in these minerals, and therefore the magnetic stability of the samples bearing them. We present results from micromagnetic simulations of titanomagnetite ellipsoids of varying shape and composition to find the size ranges of the single domain (SD) and SV structures. These size ranges overlap, allowing for regions where the SD and SV structures are both available. These regions are of interest as they may lead to magnetic instability and "partial thermal remanent magnetization (pTRM) tails" in paleointensity experiments. We find that although this SD + SV zone occupies a narrow range of sizes for equidimensional magnetite, it is widest for intermediate (TM30‐40) titanomagnetite compositions, and increases for both oblate and prolate particles, with some compositions and sizes having an SD + SV zone up to 100s of nm wide. Our results help to explain the prevalence of pTRM tail‐like behavior in paleointensity experiments. They also highlight regions of particles with unusual domain states to target for further investigation into the definitive mechanism behind paleointensity failure. Plain Language Summary: Rocks that record Earth's magnetic field often contain the mineral magnetite. The crystal structure of magnetite allows titanium atoms to substitute for iron, giving rise to a range of minerals known as titanomagnetites. The internal magnetic structure of titanomagnetite particles in rocks, known as the "domain structure," controls the ability of that particle to record magnetic fields. Particles with certain kinds of domain structure are unstable magnetic recorders, which can cause problems for experiments trying to determine Earth's magnetic field strength in the past (paleointensity experiments). Although the domain structures in magnetite are well understood, there are no recent studies which describe them in titanomagnetites. In this paper, we simulate the domain structures in small titanomagnetite particles and map these out as a function of size, shape and chemical composition. In doing so, we identify types of magnetic particles with multiple possible domain structures that may give rise to unstable magnetizations. Our results indicate that some titanomagnetite particles may have unstable magnetizations over a much larger range of sizes than has previously been seen in magnetite. This wide range of sizes could explain the high failure rates of paleointensity experiments. Key Points: We systematically map out the domain states in titanomagnetite as a function of shape and compositionOur results highlight ranges of compositions, shapes and sizes which contain unreliable paleomagnetic recordersFor certain shapes and compositions, these regions span hundreds of nanometers, representing a significant proportion of remanence carriers [ABSTRACT FROM AUTHOR]

Interplanetary (IP) shocks are one of the dominant solar wind structures that can significantly impact the Geospace when impinge on the Earth's magnetosphere. IP shocks severely distort the magnetosphere and induce dramatic changes in the magnetospheric currents, often leading to large disturbances in the geomagnetic field. Sudden enhancements in the solar wind dynamic pressure (PDyn) during IP shocks cause enhanced high‐latitude convection electric fields which penetrate promptly to equatorial latitudes. In response, the equatorial electrojet (EEJ) current exhibits sharp changes of magnitudes primarily controlled by the change in PDyn and the local time. In this paper, we further investigated the influence of shock impact angle on the EEJ response to a large number (306) of IP shocks that occurred during 2001–2021. The results consistently show that the EEJ exhibits a heightened response to the shocks that head‐on impact the magnetosphere (frontal shocks) than those with inclined impact (inclined shocks). The greater EEJ response during the frontal shocks could be due to a more intensified high‐latitude convection electric field resulting from the symmetric compression of the magnetosphere. Finally, an existing empirical relation involving PDyn and local time is improved by including the effects of impact angle, which can quantitatively better predict the EEJ response to IP shocks. Plain Language Summary: Solar Wind, a continuous stream of high‐energy particles emanating from the Sun, is ubiquitous in interplanetary (IP) space. In unison, the energetic and/or transient eruptions on the Sun often release bursts of fast solar wind. When this fast solar wind interacts with the ambient solar wind in the IP space, a shock front is formed known as IP shock. These IP shocks (if Earth‐directed) can impinge on the Earth's magnetosphere and transfer tremendous amounts of energy and momentum. As a result, the Earth's magnetic field is often severely disturbed. Severe geomagnetic disturbances are known to cause a myriad of space weather effects from the loss of satellites in space to damage of electrical power grids and transmission lines on ground. Historically, geomagnetic field disturbances are known to be more cataclysmic at high latitudes and lessen at latitudes below the auroral region. However, these disturbances again dramatically enhance at equatorial latitudes due to a unique ionospheric current system, known as equatorial electrojet (EEJ). This study provides new insights into the significant role of angle of shock impacting the magnetosphere and the resultant disturbances in EEJ. This study also derives an empirical relation to accurately estimate the EEJ disturbances during IP shocks. Key Points: The angle of interplanetary (IP) shock impact on the magnetosphere plays a significant role in controlling the equatorial electrojet (EEJ) responseThe magnitude of EEJ change due to the impact of frontal IP shocks is significantly larger than that for the inclined shocksAn improved empirical relation including the effects of impact angle is derived which provide better estimates of EEJ responses to IP shocks [ABSTRACT FROM AUTHOR]

This paper investigates the formation and segmentation of the tongue of ionization into two consecutive polar cap patches using multi‐instrument observations from 27 February 2014. We provide insights into how the interplanetary magnetic field (IMF) variations influence the formation and segmentation of these patches. Our findings reveal that the entry of dayside dense plasma into the polar cap is predominantly driven by the modified convection near the cusp region, which is controlled by the transition of IMF By or the sudden drop of IMF Bz. Furthermore, we observe a rapid north‐westward plasma flow within the patch segmentation region, accompanied by equatorward‐expanded and enhanced convection near the cusp region. This fast‐moving flow, approximately 1.5 km/s, is characterized by low density and high electron temperature and shows a signature of a Subauroral Polarization Stream. This suggests that the fast‐westward flow, in conjunction with the expansion and contraction of ionospheric convection, plays a crucial role in the segmentation of polar cap patches from the dayside plasma reservoir. This study provides a comprehensive observation of the evolution of polar cap patches, thereby advancing our understanding of the dynamic mechanisms governing patch formation and segmentation. Plain Language Summary: Polar cap patches are highly dense structures in the polar cap region, typically forming in the cusp region and moving toward the nightside due to ionospheric convections. To better understand the factors that govern the formation and segmentation of these patches, a combination of satellite and ground‐based observations is used to investigate two consecutive polar cap patches on 27 February 2014. We found that the configuration of IMF By and Bz significantly influences cusp region convection, causing dayside sunlit dense plasma to enter the polar cap when cusp convection expands equatorward and the flow shifts northward, a process that leads to patch formation. Additionally, we observe strong north‐westward flows of low‐density, high‐electron‐temperature plasma in the subauroral region during periods of geomagnetic disturbance, displaying characteristics of Subauroral Polarization Streams (SAPS). This flow is observed in the patch segmentation region along with the equatorward‐expanding, enhanced cusp convection. These observations indicate that SAPS, along with the expansion and contraction of ionospheric convection, play a key role in the segmentation of polar cap patches from their equatorward plasma reservoir. This study significantly advances our understanding of the dynamic mechanisms governing the formation and segmentation of polar cap patches. Key Points: The transient change of IMF By and Bz leads to the formation of the tongue of ionization and segmentation of polar cap patchesA tongue of ionization is segmented into two polar cap patches by low electron density, high electron temperature, fast westward flowsThe expansion/contraction of the ionospheric convection also plays a crucial role in the segmentation of dayside dense plasma [ABSTRACT FROM AUTHOR]

From the global simulation, we reproduce the solar wind‐magnetosphere‐ionosphere (S‐M‐I) interaction under the northward interplanetary magnetic field (IMF) with negative By. Reconnection structures, the plasma sheet, and lobes are formed in magnetospheric convection, while lobe/round‐merging/reciprocal/nightside cells appear in the ionosphere. Associated with the S‐M interaction, northern open field is generated at the evening open‐closed (O/C) boundary, due to successive cusp and interchange reconnections (in round‐merging cell) or by Dungey‐type reconnection (in nightside cell). Corresponding interchange and Dungey‐type reconnections occur at the southern null. Dungey‐type reconnection at the same time generates southern open field on the outer‐most magnetopause. Open field injected into the northern polar cap/void/lobe constructs the open field part of the round‐merging and nightside cells. After open‐field convection in the lobe, reclosures occur by again successive cusp and interchange reconnections on the dayside separator, or separator reconnection on the nightside separator. Former closed field line proceeds toward the evening O/C boundary through the dayside closed‐field convection in the round‐merging cell, while latter closed field line through the nightside closed‐field convection in the nightside cell. Shear that causes the large‐scale sun‐aligned arc is generated by the process of injecting open magnetic field into the void and the conjugate of process of connecting return flux from the plasma sheet to the nightside cell in counter hemisphere. Key Points: Under the northward IMF, the S‐M interaction has in front and off‐front components exciting the round‐merging cell and the nightside cellIn the nightside cell, closed flux is formed at nightside separator and transported along the nightside cell to the flank where reopenedThe HCA is explained by shear structure presented in this paper, without adopting evening‐morning symmetrical convection as in the DLR [ABSTRACT FROM AUTHOR]

Using an in–house developed Quasi Two–Dimensional (QTD) physics–based ionospheric model, the impact of E × B drift velocity on the vertical distribution of the electron density over the equatorial latitude has been investigated. The vertical drift measurements from (a) drift analysis software of Digisonde (b) derived from Digisonde ionograms (c) calculated from the Scherliess–Fejer (SF) model, and (d) obtained from the magnetometer ΔH measurements have been used in this study. Four quiet days in a low solar activity year, representing four seasons of the year 2010, have been chosen for the study. The model–derived electron density profiles using the vertical drifts from all four methods matched well with the Digisonde observation below ∼150 km at all the Local Times (LTs) for all 4 days. However, since the Digisonde–derived drifts were very low, centered mostly around zero, it led to the overestimation/underestimation of the F–region peak plasma density (nmF2)/height (hmF2). The model simulated electron density profiles using the SF model, and ΔH derived vertical drifts showed good agreement with the observation up to an altitude of ∼350 km. The study showed that vertical drift is a factor that controls the nmF2 trough around noon over the equatorial latitude. It is seen that plasma diffusion occurs only beyond an altitude of 350 km, while the range of altitudes between 320 and 350 km acts as the "diffusion threshold height." This finding has significant implications for understanding plasma dynamics in the equatorial ionosphere. Plain Language Summary: The present study employed a quasi–two–dimensional theoretical ionospheric model to investigate the impact of vertical drift on the electron density distribution over the equatorial ionosphere. Utilizing vertical drift values derived from Digisonde, Scherliess–Fejer (SF) model calculations, and magnetometer readings, the model was simulated for four distinct days of 2010 representing the four seasons of the year. The electron density profiles generated using all four techniques exhibited a close match to the observed values for all 4 days. However, when very low Digisonde–derived drifts were employed, an overestimation of the F–region density and an underestimation of peak F–region plasma density heights were observed. The study demonstrated that the model–simulated electron density profiles, generated using the SF model and magnetometer–derived vertical drifts, exhibited excellent agreement with the observed profiles at altitudes up to approximately 350 km. Similar variations of the calculated and observed nmF2 values led to the conclusion that vertical drift is a crucial factor in controlling the equatorial noon–time nmF2 trough. Furthermore, the study revealed that plasma diffusion occurred only beyond an altitude of 350 km as the altitude range of 320–350 km acts like a "diffusion threshold height." Key Points: This paper studies the impact of vertical drift on the vertical distribution of the electron densityThe plasma vertical drift plays an important role in the noon time nmF2 troughThe altitude range 320–350 km can be called as the plasma "diffusion threshold height" [ABSTRACT FROM AUTHOR]

Evaluating the impact of geomagnetic disturbances on power grid infrastructure is critical to mitigate the risk posed by geomagnetically induced currents (GICs). In this paper, the geoelectric field and induced voltage distribution in North China were estimated from the SinoProbe magnetotelluric (MT) impedance data together with the geomagnetic observatory data of six INTERMAGNET stations recorded during the significant geomagnetic storm of 17th March 2015. The measured impedances from 119 SinoProbe MT sites were convolved with geomagnetic observatory data to account for the Earth's complex three-dimensional electrical resistivity structure. The resultant geoelectric field was then used to model the induced voltage distribution across the regional power transmission network in North China. Due to the large inter-site distances of the SinoProbe MT program, the derived geoelectric field is mostly homogeneous, except in the Ordos Basin that displays a polarization of the geoelectric field, and with higher magnitudes in the orogenic belts. The estimated geoelectric fields in Taihang-Lvliang, Yanshan, and Luxi orogenic belts of North China were large (>1 V/km) during the storm, due to high-resistivity lithosphere resulting in large voltage gradients in the Earth. However, in relation to locations of major power transmission lines, only the central part of North China experienced induced voltages exceeding 100 V. [ABSTRACT FROM AUTHOR]

This manuscript presents the analysis of data from multiple ground‐ and space‐based sensors in the North American region before, during, and after the 12 October 2021 geomagnetic storm. Total electron content (TEC) and electron density data show the formation and equatorward propagation of a mid‐latitude trough at ∼50°N followed by the appearance of a wider depletion region (∼15° in latitude) at lower latitudes. During the recovery phase on the 13th, the equatorward edge of this depletion region settled at around 30° latitude and exhibited a steep density gradient. By the 14th, this sharp boundary had disappeared. Near this edge on the 13th, small‐scale irregularities formed. The impact of these was observed within Global Positioning System data as elevated rate of TEC index (ROTI) and presented as strong 35 MHz scintillations of cosmic radio sources as well as spread‐F within ionograms from multiple digisonde systems. GPS and 35‐MHz data demonstrated that the irregularity region was narrowly confined (≲5° wide) near the edge of the depletion region. The 35‐MHz scintillation data also showed that the irregularities were moving relatively slowly at ∼7 m s−1, likely toward the southeast. Density and velocity measurements demonstrated that the conditions near the depletion boundary were highly favorable to the gradient drift instability (GDI) with the one‐dimensional growth rate estimated to be ∼0.01 s−1. Since these conditions persisted for many hours, this growth rate was more than sufficient for the GDI to be considered the primary driver of irregularity formation in this case. Plain Language Summary: Earth's ionosphere, the ionized portion of the upper atmosphere, is a dynamic environment, often beset with irregularities and disturbances that interfere with radio frequency signals that travel through it. In this regard, mid‐latitudes are usually quite tame relative to the equatorial and polar regions. However, when significant geomagnetic disturbances, or "storms," occur, this normally placid region can become anything but. This paper presents the results of a study that examines the impact of a storm over North America, using several space‐ and ground‐based sensors. Of particular interest is the formation of a density depletion region during the recovery period following the onset of the storm. Multiple sensors show evidence of this depletion and still others show a preponderance of small‐scale irregularities (as small as a few kilometers) near its southern boundary. A holistic analysis indicates that these irregularities are consistent with a turbulent cascade moving relatively slowly, likely toward the south or southeast. Conditions near the depletion edge were observed to be conducive with the so‐called gradient drift instability. This is known to be a primary driver of irregularity formation within other settings, and appears to be the culprit in this case as well. Key Points: A multitude of ground‐ and space‐based sensors were used to study a storm‐induced mid‐latitude ionospheric depletion over North AmericaIrregularities at the equatorward edge of the depletion at ∼30°N were detected with radio frequency systems from a few MHz to 1.5 GHzSpace‐based in situ and remote sensing data point to the gradient drift instability as the most likely driver of irregularity formation [ABSTRACT FROM AUTHOR]