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Plasma sheet convection is a key element of storm‐time plasma dynamics in the magnetosphere. While decades of observations have advanced our understanding of convection in general, specifically storm‐time convection remains poorly understood. Using data from ISAS/NASA's Geotail and NASA's MMS, this study characterizes plasma sheet magnetic flux transport across the magnetotail during numerous storms (both recovery and main phases) and contrasts these observations with those from quiet times. Our findings confirm the well‐documented enhancement of the convection electric field during geomagnetic storms. Beyond that, our results reveal a significant dawn‐dusk asymmetry. At dawn, the elevated convection is realized via relatively faster flows while at dusk, through a stronger northward magnetic field. These findings suggest a complex feedback loop between plasma sheet convection and ring current buildup, whereby the latter asymmetrically inflates the magnetotail on the dusk side, shifting the reconnection site and subsequently enhanced earthward flows toward dawn. Plain Language Summary: Strong solar activity creates major disruptions of the Earth's magnetic field known as geomagnetic storms. These major disturbances of near‐Earth space can impact essential technologies like GPS systems and power grids. Our research used data from two space missions, ISAS/NASA's Geotail and NASA's MMS, to study how particles and magnetic fields move in space around Earth during such storms. We compared storm periods to calm times and evaluated the differences. During geomagnetic storms, we found that charged particles transport more magnetic flux due to stronger electric field. We further noted a significant difference between the dawn (morning) and dusk (evening) sectors on the nightside of the near‐Earth space environment. During storm times, plasma moves faster on the dawn side, while the magnetic field is stronger on the dusk side. This discovery reveals that plasma movement and energy buildup during storms are more complex than we thought. The energy buildup on the dusk side pushes plasma movement more toward the dawn side. Understanding these details helps us better predict the impacts of geomagnetic storms on Earth's space environment, which can improve our ability to protect our technology and infrastructure. Key Points: Convection electric field is elevated across the plasma sheet during storms, but convection properties are different between dawn and duskDawn magnetic flux transport during storm time is statistically associated with relatively faster flowsDusk magnetic flux transport during storm times is statistically associated with more dipolar magnetic fields [ABSTRACT FROM AUTHOR]

During magnetospheric substorms, plasma from magnetic reconnection in the magnetotail is thought to reach the inner magnetosphere and form a partial ring current. We simulate this process using a fully kinetic 3D particle‐in‐cell (PIC) numerical code along with a global magnetohydrodynamics (MHD) model. The PIC simulation extends from the solar wind outside the bow shock to beyond the reconnection region in the tail, while the MHD code extends much further and is run for nominal solar wind parameters and a southward interplanetary magnetic field. By the end of the PIC calculation, ions and electrons from the tail reconnection reach the inner magnetosphere and form a partial ring current and diamagnetic current. The primary source of particles to the inner magnetosphere is bursty bulk flows (BBFs) that originate from a complex pattern of reconnection in the near‐Earth magnetotail at xGSM=−18RE ${x}_{\text{GSM}}=-18{R}_{\mathrm{E}}$ to −30RE ${-}30{R}_{\mathrm{E}}$. Most ion acceleration occurs in this region, gaining from 10 to 50 keV as they traverse the sites of active reconnection. Electrons jet away from the reconnection region much faster than the ions, setting up an ambipolar electric field allowing the ions to catch up after approximately 10 ion inertial lengths. The initial energy flux in the BBFs is mainly kinetic energy flux from the ions, but as they move earthward, the energy flux changes to enthalpy flux at the ring current. The power delivered from the tail reconnection in the simulation to the inner magnetosphere is >2×1011 ${ >} 2\times 1{0}^{11}$ W, which is consistent with observations. Plain Language Summary: During intervals of increased solar activity, the magnetic field in Earth's stretched night‐side tail undergoes intense reconfiguration that can energize particles. This process is called magnetic reconnection. Ions and electrons from reconnection can reach the inner magnetosphere. In this paper, we simulate this process using a novel model that includes Earth's global magnetic field configuration and self‐consistently models particle physics for both electrons and ions. We find that the particles are accelerated significantly near the sites of magnetic field reconfiguration with ions gaining 10 s of keV energy. As they propagate earthward, they end up contributing energetically to the formation of a ring current system partially encircling Earth. Key Points: Ions and electrons accelerated by 10–50 keV near the magnetotail reconnection can reach the inner magnetosphereA partial ring current is formed during the simulation, with highest energy flux between midnight and duskThe ion and electron energy fluxes are mostly kinetic in the reconnection region but change to enthalpy flux earthward [ABSTRACT FROM AUTHOR]

A detailed analysis is made of horizontal‐component geomagnetic‐disturbance data acquired at the Colaba observatory in India recording the Carrington magnetic storm of September 1859. Prior to attaining its maximum absolute value, disturbance at Colaba increased with an e‐folding timescale of 0.46 hr (28 min). Following its maximum, absolute disturbance at Colaba decreased as a trend having an e‐folding timescale of 0.31 hr (19 min). Both of these timescales are much shorter than those characterizing the drift period of ring‐current ions. Furthermore, over one 28‐min interval when absolute disturbance was increasing, the data indicate an absolute rate of change of ≥2,436 nT/hr. If this is representative of disturbance generated by a symmetric magnetospheric ring current, then, assuming a standard and widely used parameterization, an interplanetary electric field of ≥451 mV/m is indicated. An idealized and extreme solar‐wind dynamic pressure could, conceivably, reduce this bound on the interplanetary electric field to ≥202 mV/m. If the parameterization for electric‐field extrapolation is accurate, but the field strengths obtained are deemed implausible, then it can be concluded that the Colaba disturbance data were significantly affected by partial‐ring, field‐aligned, or ionospheric currents. The same conclusion is supported by the shortness of the e‐folding timescales characterizing the Colaba data. Several prominent studies of the Carrington event need to be reconsidered. Key Points: Before (after) maximum, the absolute value of disturbance at Colaba increased (decreased) with an exponential timescale of 0.46 hr (0.31 hr)If Colaba disturbance was due to a symmetric ring current, standard extrapolations require an interplanetary electric field of >451 mV/mResults suggest significant contributions to Colaba disturbance by partial‐ring, dayside field‐aligned, or dayside ionospheric currents [ABSTRACT FROM AUTHOR]

Adiabatic motion is a fundamental reversible process for geomagnetically trapped particle populations, including particles comprising the ring current and radiation belts. During adiabatic motion, a particle's trajectory in configuration space responds to sufficiently slow changes in the magnetospheric magnetic field. Previous research has highlighted expected patterns in adiabatic motion, such as radial motion or the Dst effect. In this work, we introduce a method we call Invariant Matching for quantifying adiabatic motion between a pair of magnetospheres. This method can be applied to both simulation and semi-empirical magnetic field models, is computationally efficient, and in particular does not require tracing the particle trajectories. In this work, we use the Tsyganenko et al., Journal of Geophysical Research: Space Physics, 2005, 110 (TS05) magnetic field model, and present adiabatic motion between a storm commencement, the time of the storm's Dst minimum, and a nominal recovery time. We also analyze adiabatic motion which occurs in response to enhancements of individual major current systems (including the ring current, Chapman-Ferraro current, Birkeland current, and tail current). Our methodology yields vector fields quantifying the displacement of mirror points throughout the magnetosphere, prepared in a way appropriate for application to both outer radiation belt and ring current populations. [ABSTRACT FROM AUTHOR]

This work reports the magnetic index of aromaticity of cyclophosphazene (c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$H6$$ {}_6 $$) and their halogenated cyclic derivatives: c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$F6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Cl6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Br6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$I6$$ {}_6 $$, c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$At6$$ {}_6 $$ and c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$Ts6$$ {}_6 $$. This index, also known as ring‐current strength, is calculated by numerical integration of the magnetically‐induced current density vector field which is generated by a perturbing external magnetic field. Due to the presence of heavy X=Br,I,At$$ \mathrm{X}=\mathrm{Br},\mathrm{I},\mathrm{At} $$ atoms in c$$ c $$‐P3$$ {}_3 $$N3$$ {}_3 $$X6$$ {}_6 $$, important relativistic were expected. Accordingly, all‐electron density functional theory (DFT) calculations were carried out using the four‐component Dirac‐Coulomb (DC) Hamiltonian, including scalar and spin‐orbit relativistic effects. The values were also compared with the corresponding spin‐free (scalar relativistic) ones. [ABSTRACT FROM AUTHOR]

Magnetic field line curvature (FLC) scattering is an effective mechanism for collisionless particle scattering. In the terrestrial magnetosphere, the FLC scattering plays an essential role in shaping the outer boundary of protons radiation belt, the rapid decay of ring current, and the formation of proton isotropic boundary (IB). However, previous studies have yet to adequately investigate the influence of FLC scattering on charged particles in the Earth's dayside magnetosphere, particularly in the off‐equatorial magnetic minima regions. This study employs T89 magnetic field model to investigate the impacts of FLC scattering on ring current protons in the dayside magnetosphere, with a specific focus on the off‐equatorial minimum regions. We analyze the spatial distributions of single and dual magnetic minima regions, adiabatic parameter, and pitch angle diffusion coefficients due to FLC scattering as functions of Kp. The results show that the effects of FLC scattering are significant not only on the dusk and dawn sides but also in the off‐equatorial minima regions on the noon. Additionally, we investigate the role of dipole tilt angle in the hemispheric asymmetry of FLC scattering effects. The dipole tilt angle controls the overall displacement of the dayside magnetosphere, resulting in different FLC scattering effects in the two hemispheres. Our study holds significance for understanding the FLC scattering effects in the off‐equatorial region of Earth's dayside magnetosphere and for constructing a more accurate dynamic model of particles. Key Points: Ring current protons in the dayside off‐equatorial regions are significantly affected by field line curvature (FLC) scatteringThe scattering effects driven by FLC on protons display distinct hemispheric asymmetry in the dayside off‐equatorial regionsThe dipole tilt angle affects hemispheric asymmetry, thereby influencing the strength and extent of FLC scattering [ABSTRACT FROM AUTHOR]

• We model precipitating electron fluxes, and investigate sensitivity of the model to the boundary conditions. • The dynamics of the modeled precipitating electron fluxes are qualitatively similar to POES observations at >30 keV and >100 keV. • We compute and validate ionization rates based on precipitating flux, which can be used in atmospheric models. Electron and ion fluxes at energies of ∼10 keV−1 MeV can change by orders of magnitude during geomagnetically active periods. This can lead to intensification of particle precipitation into the Earth's atmosphere. The process further affects atmospheric chemistry, which may impact weather and climate on the Earth's surface. In this study, we concentrate on ring current electrons, and investigate precipitation mechanisms using a numerical model based on the Fokker-Planck equation. We focus on a study of the main precipitation mechanisms, and their connection with atmospheric parameters. We investigate the 17 March 2013 storm using the convection–diffusion 4-Dimensional Versatile Electron Radiation Belt (VERB-4D) code, that allows us to quantify the impact of the storm on the electron ring current, and the resulting electron precipitation. We validate our results against observations from the Polar Operational Environmental Satellites (POES) mission, the low Earth orbiting meteorological satellites National Oceanic and Atmospheric Administration (NOAA-15,-16,-17,-18,-19), and Meteorological Operational Satellite MetOp-02, as well as the Van Allen Probes, and produce a data set of precipitating fluxes that covers an energy range from 10 keV to 1 MeV. We calculate the altitude-dependent atmospheric ionization rates, a prerequisite for atmospheric models to estimate effects of geomagnetically active periods on chemical and physical variability of the atmosphere at high latitudes. Atmospheric ionization rates are validated against Atmospheric Ionization during Substorm (AIMOS 2.1-Aisstorm) and Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) values, and show good agreement at high geomagnetic latitudes during the storm time. [ABSTRACT FROM AUTHOR]

During geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region. Key Points: Superposed epoch analysis shows dynamic evolution of O+ ions during geomagnetic stormsSignificant enhancement of the O+‐to‐H+ number density ratio observed at radial distances less than 12 REScalar temperature for both species show the arrival of heated ions far from Earth throughout the analyzed period [ABSTRACT FROM AUTHOR]

We present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons. Plain Language Summary: During magnetic storms and substorms, energetic ions are sporadically injected into the geospace, which distorts the stable population and velocity distributions of ions in space. At these moments, various plasma instabilities lead to ultra‐low frequency (ULF) wave excitations. The lowest‐frequency waves in the ULF range have a wavelength comparable to the size of the Earth and are typically analyzed using magnetohydrodynamic principles. This approach considers the plasma environment using macroscale parameters such as pressure and density. In this paper, we report a spacecraft observation of a broadband compressional ULF wave that cannot be interpreted using magnetohydrodynamics. Such waves have rarely been reported and analyzed; however, their interaction with energetic ions is important to understand magnetospheric energy dynamics. The plasma conditions were described using the kinetic theory, which involves particle velocity distributions. We observed that a drift resonance occurred between the energetic protons and waves, while the gradient instability condition was satisfied for a part of time. Therefore, we concluded that the wave was in a drift‐compressional mode excited through drift resonance and gradient instability. The interpretation of compressional waves via satellite observations of energetic ions has been receiving increasing attention to understand their excitation mechanism. Key Points: Pc4–5 compressional ultra‐low frequency waves with an azimuthal wave number of −130 were observed in the nose structure on dusksideTheoretically predicted values of drift‐compressional mode frequency match the observed wave frequencyBoth radial ion temperature gradient and drift resonance of 20–25 keV protons serve as energy sources of the wave [ABSTRACT FROM AUTHOR]

• Formation of low magnetic field region (dent) in Earth's magnetosphere during intense storm. • Altitude and mirror points of charged particles get affected by magnetic field hump and dent. • The dent in magnetic field is formed closer to the Earth as strength of ring current increases. The development of the ring current through a westward circulation of energetic ions around the Earth in the low latitude region during geomagnetic storms has been known to us for the past several decades. The symmetric part of the ring current exists in the form of a ring around the Earth at a distance of ≈ 3–7 R e from the center of the Earth. The location and strength of the ring current is mainly controlled by the interplanetary solar wind conditions. The presence of such external current forms the additional mini magnetic dipole in the vicinity of the Earth's space, which eventually affects the geomagnetic field configuration. The magnetic field produced due to the ring current opposes the geomagnetic field inside and adds to the geomagnetic field outside the location of the ring current. This scenario has been modelled in this paper by using a circular loop of uniform current around the Earth to represent the ring current flow around the Earth. The aim of the present study is to understand the overall changes in the magnetic field and its influence on the radiation belt energetic (MeV range) electrons and protons during a geomagnetic storm. The model calculations suggest the formation of low and high magnetic field regions (here referred to as dent and hump) in the Earth's magnetosphere due to intense westward ring current. The size and position of these low and high magnetic field regions are controlled by the strength and location of the ring current. It is found that both the altitudinal reach and mirror point of the bouncing-drifting radiation belt energetic particles are significantly affected by the presence of the dent and the hump in the magnetic field driven by the ring current. The decrease in ground magnetic field of 1700 nT or more, which is similar to the geomagnetic field variation observed during the historic Carrington event, is possible with the peak ring current strength of 20–30 MA situated at a distance of 2 R e or less from the center of the Earth. [ABSTRACT FROM AUTHOR]

The present study uncovers the fine structures of magnetosonic waves by investigating the EFW waveforms measured by Van Allen Probes. We show that each harmonic of the magnetosonic wave may consist of a series of elementary rising‐tone emissions, implying a nonlinear mechanism for the wave generation. By investigating an elementary rising‐tone magnetosonic wave that spans a wide frequency range, we show that the frequency sweep rate is likely proportional to the wave frequency. We studied compound rising‐tone magnetosonic waves, and found that they typically consist of multiple harmonics in the source region, and may gradually become continuous in frequency as they propagate away from source. Both elementary and compound rising‐tone magnetosonic waves last for ∼1 min which is close to the bounce period of the ring proton distribution, but their relation is not fully understood. Plain Language Summary: Naturally occurring magnetosonic waves are a kind of electromagnetic wave in the Earth's magnetized space. Their frequency spectra typically exhibit a harmonic structure. Sometimes they exhibit a rising‐tone feature, that is, the wave starts at a low pitch and gradually increases its frequency to a high pitch. Using the high‐resolution data measured by Van Allen Probe satellites, the present study uncovers that each harmonic of a magnetosonic wave may have a fine structure: they consist of a series of elementary rising‐tone emissions. The traditionally known rising‐tone magnetosonic waves consist of multiple harmonics, and we name them "compound rising‐tone magnetosonic waves". The compound rising‐tone waves may gradually become continuous in spectrum as they propagate away from source. These findings give new insights to the generation of magnetosonic waves and their impact on space environment. Key Points: Each harmonic of a magnetosonic wave may consist of a series of elementary rising‐tone emissionsThe frequency sweep rate of elementary magnetosonic waves is likely proportional to the frequencyCompound rising‐tone magnetosonic waves consist of harmonics at the source, and gradually develop a continuous spectrum during propagation [ABSTRACT FROM AUTHOR]

Adiabatic motion is a fundamental reversible process for geomagnetically trapped particle populations, including particles comprising the ring current and radiation belts. During adiabatic motion, a particle’s trajectory in configuration space responds to sufficiently slow changes in the magnetospheric magnetic field. Previous research has highlighted expected patterns in adiabatic motion, such as radial motion or the Dst effect. In this work, we introduce a method we call Invariant Matching for quantifying adiabatic motion between a pair of magnetospheres. This method can be applied to both simulation and semi-empirical magnetic field models, is computationally efficient, and in particular does not require tracing the particle trajectories. In this work, we use the Tsyganenko et al., Journal of Geophysical Research: Space Physics, 2005, 110 (TS05) magnetic field model, and present adiabatic motion between a storm commencement, the time of the storm’s Dst minimum, and a nominal recovery time. We also analyze adiabatic motion which occurs in response to enhancements of individual major current systems (including the ring current, Chapman-Ferraro current, Birkeland current, and tail current). Our methodology yields vector fields quantifying the displacement of mirror points throughout the magnetosphere, prepared in a way appropriate for application to both outer radiation belt and ring current populations.

In this study we investigate the role of particle injections on the ring current development during the 7-8 September 2017 geomagnetic storm by applying a temporally and spatially varying data-driven outer boundary condition in numerical simulations of the ring current with the Comprehensive Inner Magnetosphere-Ionosphere model. We quantify the role of particle injections by comparing the results from two simulation runs: one with the model outer boundary condition defined by measurements at their original time cadence, namely, 1.5 min, and one with the same boundary condition smoothed in time with a 2-h running average window. The comparison between these two runs reveals that the observed particle injections enhanced the electric field remarkably, which had a significant effect on the ring current development, namely, they 1) strengthened the ring current, 2) skewed the ring current distribution dawnward, 3) delayed the formation of the symmetric ring current by prolonging the duration of the partial ring current, and 4) caused a O+-richer ring current with a O+ dominant ring current distribution at the inner edge. Furthermore, these effects enhanced the energy deposition to the plasmasphere and ionosphere via heating by the ring current ions. [ABSTRACT FROM AUTHOR]

The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on both the Van Allen Probes spacecraft is a time-of-flight versus total energy instrument that provided ion composition data over the ring current energy (∼7 keV to ∼1 MeV), and electrons over the energy range ∼25 keV to ∼1 MeV throughout the duration of the mission (2012 – 2019). In this paper we present instrument calibrations, implemented after the Van Allen Probes mission was launched. In particular, we discuss updated rate dependent corrections, possible contamination by "accidentals" rates, and caveats concerning the use of certain products. We also provide a summary of the major advances in ring current science, obtained from RBSPICE observations, and their implications for the future of inner magnetosphere exploration. [ABSTRACT FROM AUTHOR]

Potential analysis (PA) method is used to investigate the randomness or stochastic noise in 1-minute Dst and SYM-H data during highly disturbed as well as solar minimum quiet periods. This method is helpful in understanding the behaviour of a system whose internal parameters are unknown. The effect of random noise is exhibited in the number of wells in the potential function and in the bifurcation of states. Higher the number of state, higher the effect of random noise in the system. Our study focuses on PA of 12 intense geomagnetic storms of solar cycle (SC) 23 with peak Dst ≤ –200 nT and 12 quiet events with Dst ≥ –50 nT during solar minimum periods, using 1-minute Dst and SYM-H data for a period of 10 days each. Storm phases were least affected by random noise, while undisturbed periods were episodes of higher noisy states. Random noise in the indices can be attributed to different factors, including the effect of solar wind dynamic pressure on Dst estimation, contribution of different ion species to ring current, storm time super substorms, etc. Role of other factors is subjected to further analysis. Research highlights: Different noisy states of Dst and SYM-H indices during disturbed and noisy periods are studied using the method of potential analysis. Storm phases are found to be least affected by noise Pre-storm and post storm periods transit to higher noisy states from noiseless storm phases. Solar minimum quiet periods are episodes of higher random noise compared to other disturbed periods. Random noise in the indices can be attributed to different factors like SW dynamic pressure, geomagnetic energy, ion contributions to ring currents, storm time substorms etc. [ABSTRACT FROM AUTHOR]

The geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm‐enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric‐ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the 31 March 2001 storm using the Multiscale Atmosphere‐Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub‐auroral polarization stream (subauroral polarization streams (SAPS)) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy‐dependent gradient/curvature drifts and the E × B drifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase. Key Points: The first whole geospace simulation to demonstrate coherent storm‐time evolution of plasmaspheric and total electron content (TEC) plumesThe model demonstrates plasmasphere erosion and TEC depletion by the subauroral polarization streams (SAPS)SAPS is sustained by magnetospheric ion and electron distributions formed by a delicate balance of energy‐dependent and E × B drifts [ABSTRACT FROM AUTHOR]

Although both the field line curvature (FLC) and electromagnetic ion cyclotron (EMIC) waves are recognized to contribute importantly to the loss of energetic protons in the Earth's ring current, their quantitative differences in scattering ring current protons are still not fully understood. In this study, using a realistic, nondipolar magnetic field model, we perform a detailed analysis of the scattering effects of ring current protons and the resultant proton lifetimes due to FLC and EMIC waves at different L‐shells under different levels of geomagnetic activity. We find that compared with EMIC wave‐driven scattering, FLC scattering has a stronger dependence on L‐shell and geomagnetic activity. Pitch angle scattering efficiency due to FLC enhances significantly as proton energy increases. In contrast, scattering by H+ band EMIC waves tends to be weaker with increasing proton energy, while the scattering rates by He+ band EMIC waves increase first and then decrease. The results of proton lifetime against pitch angle scattering show that EMIC wave‐driven scattering dominates the loss of ring current protons at lower L‐shells (L < 6), especially during geomagnetically quiet conditions. During geomagnetically active conditions at L ≥ 6, EMIC wave‐driven scattering dominates at lower proton energies, while FLC scattering dominates at higher proton energies. This study improves the current understanding of the relative contributions of scattering by FLC and EMIC waves to the Earth's ring current proton dynamics. Key Points: We make a detailed comparison between field line curvature (FLC) and electromagnetic ion cyclotron (EMIC) waves induced scattering losses of ring current protonsFLC scattering has a stronger dependence on L‐shell and the level of geomagnetic activity than EMIC wave scatteringPronounced discrepancies are found in the dependences on proton energy and pitch angle between FLC and EMIC wave scattering [ABSTRACT FROM AUTHOR]

Abstract We present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons.

The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation of the dynamic evolution of the ring current, and establishing the corresponding relationship between key node events of the substorm. Based on the previous observation experience and our simulation results of the dynamic evolution of the ring current, we propose a macroscopic model of substorms related to the dynamic evolution of ring currents and present the possibility of confirming the causal sequence of some of those critical node events of substorms with the lunar base ENA imaging measurement. IBEX, operating in the ecliptic plane, may even give examples of the telemetry of ring current ion fluxes through ENA measurements during substorms/quiets.

Abstract Intense magnetic storms pose a systemic threat to the electric power grid. In this study we examined the solar/interplanetary causes of such storms, their peak theoretical and observed intensities, and their occurrence frequency. Using coronal mass ejection (CME) and solar wind data, we selected the 18 intense magnetic storms from 1996 to 2021 with disturbance storm time (Dst) index of less than – 200 nT and analyzed solar events and solar wind conditions associated with them. Approximately 83% of the CMEs associated with the storms were full halo type and more than 83% of the flares associated with the storms were located within 30 degrees in longitude of solar central meridian. The integrated dawn-to-dusk electric field in the solar wind (Ey) showed a good correlation with |min. Dst| of the storms and the peak Ey (Eyp) and the peak southward interplanetary magnetic field showed next good correlations with |min. Dst|. We obtained the Eyp of 236 mV/m for |min. Dst| of 2500 nT of the expected upper limit of Earth’s magnetosphere using the empirical equations from the correlations between |min. Dst| and solar wind parameters and showed that this value of Ey is possible according to the past observations. The Eyp of 54 mV/m for the 13 March 1989 storm and that of 165/79 mV/m for the Carrington storm (|min. Dst|= 1760/850 nT) were also obtained. The analysis using the complimentary cumulative distribution function suggested the probabilities of Ey of 100, 200, 250, and 340 mV/m over the next 100 years to be 0.563, 0.110, 0.060 and 0.026, respectively. Graphical Abstract

In this study we investigate the role of particle injections on the ring current development during the 7-8 September 2017 geomagnetic storm by applying a temporally and spatially varying data-driven outer boundary condition in numerical simulations of the ring current with the Comprehensive Inner Magnetosphere-Ionosphere model. We quantify the role of particle injections by comparing the results from two simulation runs: one with the model outer boundary condition defined by measurements at their original time cadence, namely, 1.5 min, and one with the same boundary condition smoothed in time with a 2-h running average window. The comparison between these two runs reveals that the observed particle injections enhanced the electric field remarkably, which had a significant effect on the ring current development, namely, they 1) strengthened the ring current, 2) skewed the ring current distribution dawnward, 3) delayed the formation of the symmetric ring current by prolonging the duration of the partial ring current, and 4) caused a O+-richer ring current with a O+ dominant ring current distribution at the inner edge. Furthermore, these effects enhanced the energy deposition to the plasmasphere and ionosphere via heating by the ring current ions.

The total energy transfer from the solar wind to the magnetosphere is governed by the reconnection rate at the magnetosphere edges as the Z‐component of interplanetary magnetic field (IMF Bz) turns southward. The geomagnetic storm on 21–22 January 2005 is considered to be anomalous as the SYM‐H index that signifies the strength of ring current, decreases and had a sustained trough value of −101 nT lasting more than 6 hr under northward IMF Bz conditions. In this work, the standard WINDMI model is utilized to estimate the growth and decay of magnetospheric currents by using several solar wind‐magnetosphere coupling functions. However, it is found that the WINDMI model driven by any of these coupling functions is not fully able to explain the decrease of SYM‐H under northward IMF Bz. A dense plasma sheet along with signatures of a highly stretched magnetosphere was observed during this storm. The SYM‐H variations during the entire duration of the storm were only reproduced after modifying the WINDMI model to account for the effects of the dense plasma sheet. The limitations of directly driven models relying purely on the solar wind parameters and not accounting for the state of the magnetosphere are highlighted by this work. Plain Language Summary: The transfer of energy from the solar wind to the Earth's magnetosphere works best when the Z‐component of interplanetary magnetic field (IMF Bz) points southward. Generally, the southward IMF Bz drives the ring current whose strength is estimated by the Dst/SYM‐H indices. The storm on 21 January 2005 is one of the rarest events as the Dst/SYM‐H index kept decreasing for more than 6 hr and reached a very low value of −101 nT after IMF Bz turned northward. In this work, we have estimated the value of SYM‐H by using various solar wind‐magnetosphere coupling functions as input to the WINDMI model. However, none of these coupling functions could estimate the unexpected decrease of SYM‐H index under the northward IMF Bz conditions. The plasma sheet was found to be highly dense during this event. The WINDMI model could successfully reproduce the SYM‐H index by incorporating this change in plasma sheet density. This investigation clearly demonstrates that the state of the Earth's magnetosphere plays a crucial role in strengthening the magnetospheric currents. Based on these findings, we suggest that space weather models need to include both the conditions of solar wind and magnetosphere to get a better prediction of the strength of the ring current. Key Points: The magnitude of SYM‐H is found to be enhanced under northward Z‐component of interplanetary magnetic field conditions present during the 21 January 2005 stormA highly dense central plasma sheet played a key role in creating the anomalous plateau phase of SYM‐HSpace weather models need to account for the state of the magnetosphere to successfully reproduce all the features of the SYM‐H index [ABSTRACT FROM AUTHOR]

The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation of the dynamic evolution of the ring current, and establishing the corresponding relationship between key node events of the substorm. Based on the previous observation experience and our simulation results of the dynamic evolution of the ring current, we propose a macroscopic model of substorms related to the dynamic evolution of ring currents and present the possibility of confirming the causal sequence of some of those critical node events of substorms with the lunar base ENA imaging measurement. IBEX, operating in the ecliptic plane, may even give examples of the telemetry of ring current ion fluxes through ENA measurements during substorms/quiets. [ABSTRACT FROM AUTHOR]

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Using data (uncorrected for the temperature effect) from the global network of neutron monitors (GNNM), along with data from the Yakutsk muon telescope complex and the muon hodoscope URAGAN (Moscow), we have applied a modified spectrographic global survey (SGS) method to the 2018 August event in order to split cosmic ray variations into components of primary, magnetospheric, and atmospheric origin. We obtained time variations in the 4 GV-rigidity primary particle isotropic flux and pitch-angle anisotropy, as well as in the interplanetary magnetic field (IMF) orientation. We also showed variations in the geomagnetic cutoff rigidity (GCR) in Irkutsk. Using the obtained data on the changes in the planetary system of GCR within a simple model of a bounded magnetosphere, we have calculated some parameters of magnetospheric current systems, namely, the ring current radius, the magnetopause current radius, and the Dst index.

Magnetopause location is an important prediction of numerical simulations of the magnetosphere, yet the models can err, either under-predicting or over-predicting the motion of the boundary. This study compares results from two of the most widely used magnetohydrodynamic (MHD) models, the Lyon–Fedder–Mobarry (LFM) model and the Space Weather Modeling Framework (SWMF), to data from the GOES 13 and 15 satellites during the geomagnetic storm on 22 June 2015, and to THEMIS A, D, and E during a quiet period on 31 January 2013. The models not only reproduce the magnetopause crossings of the spacecraft during the storm, but they also predict spurious magnetopause motion after the crossings seen in the GOES data. We investigate the possible causes of the over-predictions during the storm and find the following. First, using different ionospheric conductance models does not significantly alter predictions of the magnetopause location. Second, coupling the Rice Convection Model (RCM) to the MHD codes improves the SWMF magnetopause predictions more than it does for the LFM predictions. Third, the SWMF produces a stronger ring current than LFM, both with and without the RCM and regardless of the LFM spatial resolution. During the non-storm event, LFM predicts the THEMIS magnetopause crossings due to the southward interplanetary magnetic field better than the SWMF. Additionally, increasing the LFM spatial grid resolution improves the THEMIS predictions, while increasing the SWMF grid resolutions does not.

Claisen and Cope rearrangements are [3,3]-sigmatropic rearrangements thermally activated that occur through six-membered transition states. Although extensively investigated for decades, little is known about the magnetochemistry of these rearrangements. In view of this, we carried out an investigation based on chemical-computational models through methods based on Density Functional Theory, QTAIM, Multicenter Bond Order, NCI, GIAO, and GIMIC. We demonstrated that CCR mechanisms are concerted in which the 6-membered cyclic transition states present high aromaticity character. The molar and anisotropic susceptibility, NICS(1), and NICSzz signals were verified to have a good correlation with J (nA T−1). However, these indices demonstrated insufficient to evaluate the magnitudes of aromaticity in these transition states. Among the magnetic and topological descriptors applied in this work, the magnetically induced current density (J) proved, this to be an excellent strategy for theoretically estimative of the aromaticity of the transition states involved in the investigated rearrangements. Among the rearrangements with chair conformation, it was noted that the higher aromaticity is associated with the less favoured kinetics. For chair conformations, Claisen rearrangement (TS2) presents J = 8.63 nA T−1 and Cope (TS4) presents J = 10.43 nA T−1. However, the following order of aromaticity TS4 > TS2 > TS3 > TS1, with high paramagnetic currents in the boat conformations reducing the total current in the ring, suggests that it is not possible to establish a direct correlation between aromaticity and the kinetics of the Cope and Claisen rearrangements, since the most stable transition estate geometries are not necessarily the most aromatic. [ABSTRACT FROM AUTHOR]

Terrestrial ring current dynamics are a critical part of the near‐space environment, in that they directly drive geomagnetic field variations that control particle drifts, and define geomagnetic storms. The present study aims to specify a global and time‐varying distribution of ring current proton using geomagnetic indices and solar wind parameters with their history as input. We train an artificial neural network (ANN) model to reproduce proton fluxes measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument onboard Van Allen Probes. By choosing optimal feature parameters and their history length, the model results show a high correlation and a small error between model specifications and satellite measurements. The modeled results well capture energy‐dependent proton dynamics in association with geomagnetic storms, including inward radial diffusion, acceleration and decay. Our ANN model produces proton fluxes with their corresponding 3D spatiotemporal variations, capturing the latitudinal distribution and local time asymmetry that are consistent with observations and that can further inform theory. Plain Language Summary: The Earth's ring current is an electric current encircling the Earth at a geocentric distance of three to eight Earth radii near the magnetic equatorial plane. The enhancement of ring current causes global magnetic field variations, including decreases at the Earth's surface known as geomagnetic storms. The present study establishes a global, time‐varying model of ring current proton flux using machine learning. This model was trained using geomagnetic indices and their history as input, and proton fluxes as output. This machine learned model shows a good performance on the out‐of‐sample test set, yielding a high correlation and a low error between model results and satellite measurements. The modeled results show that the variation of proton distribution is in association with geomagnetic storms, including their inward radial diffusion, enhancement and decay. This model produces a global distribution of proton fluxes with spatiotemporal variations, capturing the latitudinal distribution and local time variations that are consistent with observations and useful for informing theory. Key Points: An artificial neural network model (RCPANN) was established to reconstruct ring current proton distributions using geomagnetic indicesThe RCPANN model successfully captures the energy‐dependent proton flux enhancement and decayThe RCPANN model captures the latitudinal variation and local time asymmetry of ring current proton distribution [ABSTRACT FROM AUTHOR]

The terrestrial ring current, flowing near the equator at the altitude of 2 RE～7 RE, is one of the most significant electric current systems of the Earth's magnetosphere. Energetic ions (~1 keV to hundreds of keV), such as protons and oxygen ions, are thought to be the main carriers of the ring current. The enhancement of ring current during geomagnetic storms is widely regarded as the main reason for the geomagnetic field disturbance. After the storm main phase, it usually takes several days (i.e., storm recovery phase) for the ring current to return to the original level of quiet times. In this paper, we present some recent studies concerning the relative contributions of different particle species, especially oxygen ions, to the ring current and the loss mechanism of the ring current during the magnetic storm recovery phase. Partial pressures of different species increase significantly at high auroral electrojet levels with hydrogen pressure being dominant inside the plasmasphere. The pressures of the heavy ions and electrons increase outside the plasmapause and develop a strong dawn-dusk asymmetry with ion pressures peaking at dusk and electron pressures peaking at dawn. In addition, ring current hydrogen with energies ranging from 50 keV up to several hundred keV is the dominant component of plasma pressure during both quiet and active times, while helium contribution is generally small. Oxygen with 10 keV < E < 50 keV and electrons with 0.1 keV < E < 40 keV become increasingly important during active times contributing more than 25% and 20% on the nightside, respectively. O+ ions' contribution to ring current is strongly connected geomagnetic activity. During large storms when sym-H0.8) and occasionally even larger than 1 when L < 3. Compared with the situation without much O+ ions contributing to the ring current, the O+ pressure and total plasma pressure are much larger when O+ ions are involved and the pressure peak moves to low L shells as sym-H decreases. Besides, the probability without much O+ is zero at most L shells when sym-H is less than −60 nT. These observational features suggest that O+ ions play an important role in the ring current during geomagnetic active times and no storm events exist without O+ ions being present. On the other hand, during relatively quiet conditions, the higher the probability, the lower of the value R. The strong correlation indicates that O+ ions are always absent during quiet times. During storm recovery phase, the observed lifetimes of H+ and O+ ions in general increase with L shell and the lifetimes of H+ ions are shorter than that of O+ ions when E < ~50 keV while the situation is reversed when E > ~50 keV, which is consistent with theory prediction. Furthermore, the observed lifetimes are in general consistent with model predictions of charge exchange lifetime, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase.

We show that time variations in the ring current and auroral electrojets in 2015, during which three major magnetic storms (MSs) occurred, are recorded in several specific ways by ground magnetometers. Specifically, we show that the time variations in magnetic field intensity have power-law wavelet spectra. The variations in ring current intensity are detected in geomagnetic field measurements of ground stations at magnetic mid-latitudes between λ = - 50 ° and + 50 °. We confirmed the results of Balasis et al. (2006), who had shown that the Dst index wavelet spectrum follows a power law of the form f - β , where f is the frequency, and β is the exponent of the power law, by applying the same wavelet analysis to the SYM-H index version of the Dst index, and also to ground magnetic field measurements. Balasis et al. (2006) also showed that the critical exponent β of the power law, obtains values greater than 2 (or equivalently that the Hurst exponent H > 0.5), shortly before the onset and during the main phase of the storms. Here, using wavelet transforms on the Earth's magnetic field as measured at different magnetic latitudes (MLAT), we showed that at mid-geomagnetic latitudes, where the Earth's magnetic field is determined mainly by the ring current, the resulting Hurst exponent is greater than 0.5 several hours before and during magnetic storms. Geomagnetic field variation at higher magnetic latitudes between λ = + 50 ° and + 73 ° , also show power-law wavelet spectra. However, here we find a more complex dependence with two power-law exponents. We interpret this double power law as the effect of both the ring current and the auroral electrojets. Finally, for polar latitudes, between λ = + 73 ° and + 85 ° , we find the same complex dependence with two power-law exponents. Our results show that the geomagnetic field at auroral latitudes has much lower power and very different wavelet spectra compared to the geomagnetic field at ranges of lower magnetic latitude. Our results show how wavelet-based measures of ground geomagnetic variations reflect the time evolution of several magnetospheric current systems. [ABSTRACT FROM AUTHOR]

Disturbance of equatorial ring current during the geomagnetic storm has dominant effect on geomagnetic field. The short term irregular variation on geomagnetic field is characterized by interaction of solar-wind magnetic field and Earth's magnetosphere, which develops time varying current in magnetosphere and ionosphere. This study represents the irregular variation on H component of Earth's magnetic field during three intense geomagnetic storm events. Among the five selected stations, four are at low-latitude and remaining one is at middle latitude. All the stations recorded the maximum depression on H component during the main phase of storm but sudden storm commencements (SSCs) event before initial phase caused slight increase in magnitude. In each of the event, low-latitude stations recorded large perturbation on magnetic field as compared to the middle latitude station. This result supports the intensification of ring current as initiated by the transfer of plasma and energy through interplanetary coronal mass ejections (ICMEs) and finally causes falling off of H component. Kakadu station (southern latitude) showed maximum value of ΔH in second and third event, this result keeps up that mostly southern hemisphere station measures large decline on H component during storm time. The calculated value of ring current and field aligned current (FAC) showed extreme negative correlation with ΔH. This unique result reveals that ring current is not only a factor that cause disturbance on horizontal component of Earth's magnetic field but FAC also has considerable effect. [ABSTRACT FROM AUTHOR]

Energetic particle injections, usually observed as sudden flux enhancements of charged particles from tens to hundreds of keV, are one of the main mechanisms for ring current enhancement. In this study, we statistically analyzed the influence of dispersionless injections on Earth's ring current based on the measurements of radiation belt storm probes ion composition experiment onboard Van Allen Probes from 2013 to 2019. We identified 813 dispersionless proton injection events, which are mainly in the pre‐midnight sector. With a greater SuperMAG electrojet index (SME), the observed injections extend to lower L shells. Meanwhile, Helium (He+) and oxygen (O+) ions experience almost simultaneous injections with protons. Superposed epoch results show that ion energy densities enhance significantly after injections. As SMEmax increases, the ring current energy densities of all three species are increasing, and the magnitude of the enhancements, defined as the ratio of the energy densities after and before the injection, hardly changes for protons (∼2.0) and He+ ions (∼2.0) but increases for O+ ions (2.6 and 3.0 for SMEmax < 1,000 nT and SMEmax ≥ 1,000 nT, respectively), suggesting the contribution of O+ ions to ring current becomes more significant during super substorms. With proton injections, the dawn‐dusk electric field is enhanced sharply to twice as large as before. Simultaneously, there is a dip followed by gradual dipolarization of the magnetic fields. Moreover, particle anisotropies increase following ion injections, which may generate electromagnetic ion cyclotron waves. These statistical results indicate that ion injections during substorms contribute significantly to the ring current. Plain Language Summary: Ring current is one of the most significant current systems in the Earth's magnetosphere, and substorm injections are major mechanisms for ring current enhancement. Dispersionless injections are considered to be in the source region, characterized by simultaneous sudden flux enhancements of charged particles from tens to hundreds of keV. Using data from Van Allen Probes, we statistically surveyed the impact of dispersionless injections on the ring current from 2013 to 2019. We found that injection events are mainly at the pre‐midnight sector, and the depth increases with stronger substorms. Along with proton injections, He+ and O+ ions are also simultaneously injected into the ring current region. The ion injections increase the energy densities of the ring current significantly, with energy densities of H+ and He+ ions increasing to twice as much as before and O+ ions rising to over 2.6 times the level before injections. Following ion injections, the configurations of the electric and magnetic fields in the ring current region change, and particle anisotropies that may generate electromagnetic ion cyclotron waves increase, leading to the loss or acceleration of inner magnetospheric particles. Key Points: We analyze the energetic particle dispersionless injections inside the geosynchronous orbit from 2013 to 2019 through RBSP observationsThe contributions of H+, He+, and O+ ion injections on the energy densities of ring current are investigated under different conditionsThe configuration of the electromagnetic fields and particle anisotropies in the ring current region change with ion injections [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron (EMIC) waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics. Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization. However, recent studies have found that the reversal of polarization, which occurs at higher latitudes along the wave propagation path, can change the wave-induced pitch angle diffusion coefficients. Whether such a polarization reversal can influence the global ring current dynamics remains unknown. In this study, we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current–atmosphere interactions model (RAM). The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or >100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized. Additionally, the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal, especially during prestorm time and the recovery phase, but the effects are not large during the main phase. This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E < 10 keV, an energy range that is not strongly affected by the polarization reversal.

Much of what we know about the solar wind’s interaction with the Earth’s magnetosphere has been gained from isolated in-situ measurements by single or multiple spacecraft. Based on their observations, we know that reconnection, whether on the dayside magnetopause or deep within the Earth’s magnetotail, controls the bulk flow of solar wind energy into and through the global system and that nightside activity provides the energized particles that power geomagnetic storms. But by their very nature these isolated in-situ measurements cannot provide an instantaneous global view of the entire system or its cross-scale dynamics. To fully quantify the dynamics of the coupled solar wind-magnetosphere requires comprehensive end-to-end global imaging of the key plasma structures that comprise the magnetosphere which have spatial resolutions that exceeds anything possible with multi-point or constellation situ measurements. Global, end-to-end, imaging provides the pathway to understanding the system as a whole, its constituent parts, and its cross-scale processes on a continuous basis, as needed to quantify the flow of solar wind energy through the global magnetospheric system. This paper describes how a comprehensively-instrumented single spacecraft in a high-altitude, high-inclination orbit coupled with ground-based instruments provides the essential observations needed to track and quantify the flow of solar wind energy through the magnetosphere. This includes observations of the solar wind plasma and magnetic field input, the magnetopause location in soft X-rays, the auroral oval in far ultraviolet, the ring current in energetic neutrals, the plasmasphere in extreme ultraviolet, the exosphere in Lyman-α, and the microstructure of the nightside auroral oval from ground-based all sky cameras.

The ring current region in the Earth's magnetosphere contains energetic charged particles, which are injected from the magnetotail, get trapped in the inner magnetosphere, and finally drift around the Earth. The current, essentially carried by ions, is caused by the differences between the drift of the positively charged ions and that of negatively charged electrons. The charge exchange that occurs between ring current ions and geocoronal atoms determines the distribution and evolution of the ring current and lays the basis for remote detection techniques. By measuring the energetic neutral atoms produced by the charge-exchange process, the ring current can be remotely detected via energetic neutral atom imaging. The Chinese Double Star Program operated the NeUtral Atom Detector Unit (NUADU) onboard one of its two satellites for more than four years. A variety of studies were conducted using multiple methods applied to observations, such as intuitive image inspection, forward modeling, and inversion. Energetic neutral atom imaging was established as a promising technique for future imaging projects. [ABSTRACT FROM AUTHOR]

The energy deposition from ring current ions into the high density "cold" plasma of the ionosphere and plasmasphere is analyzed, based on a Comprehensive Inner Magnetosphere‐Ionosphere simulation of the 2015 October 7 storm. In addition, the Naval Research Laboratory Sami3 is Also a Model of the Ionosphere ionosphere/plasmasphere code is used to simulate the effect of Coulomb‐collision heating of plasmasphere and ionosphere electrons by ring current ions. We find that, during stormtime peaks in the Dst index, energy is deposited at altitudes as low as 100 km. Heating along the entirety of any given field line, both in the ionosphere and plasmasphere, contributes to increased temperatures in the ionosphere F layer and inner magnetosphere and to subsequent cold O+ outflows. However, relative to the heating of the plasmasphere, the direct heating of the ionosphere by ring current ions produces only small effects. Qualitative model‐data agreement on the N+/O+ density ratio is consistent with the hypothesis that these outflows are driven by thermal forcing. Plain Language Summary: When the solar wind encounters Earth's magnetosphere, a geomagnetic storm can result. These storms generate a "ring current" in the inner magnetosphere. This current, carried by high energy oxygen and hydrogen ions, overlaps with the plasmasphere, a background plasma (mainly hydrogen ions) held in place by Earth's geomagnetic field. We find that the ring current also overlaps with the near‐Earth ionosphere. In previous work, we showed that, when the background plasma is heated by the ring current, oxygen ions flow upward along the geomagnetic field, producing a "heavy ion" population (the O+ shell) that has been observed. We now focus on the direct heating of the ionosphere by the ring current, versus the indirect effect where energy deposited into the higher altitude plasmasphere is conducted down to the ionosphere by electrons moving along the geomagnetic field. We find that observed stormtime ionosphere temperature increases can be explained by the heat conduction effect. Direct heating of the ionosphere by the ring current does occur during the peak of the storm, but that occurs after the ionosphere is already affected by heat conduction. Key Points: Comprehensive Inner Magnetosphere‐Ionosphere (CIMI)‐computed ring current heating is coupled into Sami3 is Also a Model of the Ionosphere to drive a simulation of the stormtime ionosphere and plasmasphereThe CIMI‐simulated model ring current is shown to directly heat both the plasmasphere and ionosphereWhen the model ring current heating is limited to plasmasphere heights, elevated ionosphere temperatures are similar to observations [ABSTRACT FROM AUTHOR]

The Van Allen Probes mission operations materialized through a distributed model in which operational responsibility was divided between the Mission Operations Center (MOC) and separate instrument specific SOCs. The sole MOC handled all aspects of telemetering and receiving tasks as well as certain scientifically relevant ancillary tasks. Each instrument science team developed individual instrument specific SOCs proficient in unique capabilities in support of science data acquisition, data processing, instrument performance, and tools for the instrument team scientists. In parallel activities, project scientists took on the task of providing a significant modeling tool base usable by the instrument science teams and the larger scientific community. With a mission as complex as Van Allen Probes, scientific inquiry occurred due to constant and significant collaboration between the SOCs and in concert with the project science team. Planned cross-instrument coordinated observations resulted in critical discoveries during the seven-year mission. Instrument cross-calibration activities elucidated a more seamless set of data products. Specific topics include post-launch changes and enhancements to the SOCs, discussion of coordination activities between the SOCs, SOC specific analysis software, modeling software provided by the Van Allen Probes project, and a section on lessons learned. One of the most significant lessons learned was the importance of the original decision to implement individual team SOCs providing timely and well-documented instrument data for the NASA Van Allen Probes Mission scientists and the larger magnetospheric and radiation belt scientific community. [ABSTRACT FROM AUTHOR]

Large-scale current systems in the ionosphere and the magnetosphere are intimately controlled by the solar wind-magnetosphere interaction and the magnetosphere-ionosphere coupling. During space weather events, these currents reconfigure and intensify significantly in response to enhanced solar wind-magnetosphere interaction, facilitating explosive energy input from the magnetosphere into the ionosphere-thermosphere system and inducing electric current surges in electric power systems on the ground. Therefore, measurements of magnetic manifestations associated with the dynamic changes of the current systems are crucial for specifying the energy input into the ionosphere-thermosphere system, understanding energy dissipation mechanisms, and predicting the severity of their space weather impacts. We investigate the potential uses of high-quality magnetic field data for space weather operations and propose real-time data products from next generation constellation missions that enable improved space weather forecasting and mitigation.

This document is a collection of research articles that explore the interconnected dynamics of the magnetosphere-ionosphere system. It covers topics such as radiation belts, aurora, current systems, and geomagnetic indices. The studies utilize various methods such as satellite and ground-based data, theory, modeling, simulations, and machine learning to investigate these phenomena. The findings contribute to our understanding of the behavior and dynamics of this complex system. The document also highlights the need for further research in this field and suggests future directions for study. [Extracted from the article]

A recent Research Article in this journal by Matito and co‐workers claimed that none of the oxidation states of a butadiyne‐linked six‐porphyrin nanoring exhibit global aromaticity or antiaromaticity. Here we show that this conclusion is incorrect. Experimental data from NMR spectroscopy for a whole family of nanorings provide strong evidence for global ring currents. The NMR data reveal these ring currents directly, without needing analysis by density functional theory (DFT). Furthermore, DFT calculations reproduce the experimental results when a suitable functional is used. [ABSTRACT FROM AUTHOR]

The main question addressed in this study is whether particles with relativistic energy can be injected directly into the inner magnetosphere by very near‐Earth reconnection during magnetic storms. We study a sequence of events observed in the solar wind, in the magnetotail, at geosynchronous orbit (GEO), in the inner magnetosphere, and in the ionosphere during the main phase of a geomagnetic storm on 16 June 2012–17 June 2012. The storm was caused by a magnetic cloud with a high dynamic pressure and a strong southward IMF lasting about 10 hr. These conditions caused an extreme compression of the magnetosphere (SymH reached ∼150 nT) and an enhancement of the lobe magnetic field strength to ∼90 nT at R ∼ 10 Earth radii (RE). We focus on an hour‐long interval between 1050 and 1150 UT on 17 June 2012 when the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites were at apogee at geocentric distances R ≈ 12 RE near midnight. At that time a thin current sheet formed between cis‐GEO distances and THEMIS. This thin current sheet reconnected between GEO and THEMIS. A strong lobe magnetic field enabled ion and electron energization to energies E ≈ 600 keV. Fluxes of high energy (up to relativistic) particles at GEO increased within ≈20 s after reconnection onset detected by THEMIS. Fluxes of relativistic electrons at L ∼ 4 in the morning sector increased within about 600 s after reconnection onset. We interpret these observations as signatures of direct injection of reconnected particles into the inner magnetosphere. Plain Language Summary: Solar flares, coronal mass ejection events may cause severe disturbances in the near‐Earth space environment called magnetic storms. During a magnetic storm the Earth magnetosphere experiences quite dramatic changes that include rapid reconfiguration of magnetic field lines that leads to conversion of the magnetic energy to kinetic and thermal energy of the space plasma (reconnection) and acceleration of charged particles. The accelerated particles and plasmas from the outer magnetosphere may penetrate deeper into the near‐Earth space, where the magnetic field is close to a dipole. Particles become trapped in the dipole field and form an electric current that flows around the Earth (ring current) and reduce the magnetic field observed on the ground. Details of the ring current formation are not well understood yet. In this paper we study a magnetic storm during which reconnection happened very close to the dipole field and particles, energized via reconnection were directly injected into the inner magnetosphere. Events like this are potentially hazardous for satellites on geosynchronous orbit and in the inner magnetosphere. Key Points: We studied space‐ and ground‐based observations during a storm caused by magnetic cloud impactOur observations suggest that a thin current sheet formed and reconnected at L about 10Reconnection caused relativistic particle injections into the inner magnetosphere [ABSTRACT FROM AUTHOR]

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. Thus, an IPA is the ionospheric projection of the spatial and temporal variation of wave‐particle interaction regions in the magnetosphere. In this study, we conducted unique multi‐event analysis of simultaneous observations of IPAs and their source regions on 22 April, 7 September, and 22 March 2018, using all‐sky imagers at subauroral latitudes and the Van Allen Probes. When the satellite footprint passed over the IPAs associated with ground Pc1 geomagnetic pulsations, locally generated He+‐band EMIC waves with the same frequencies as the ground Pc1 pulsations were observed in all events. The IPAs and EMIC waves had comparable narrow widths in the latitudinal direction. The EMIC waves appeared during the rapid enhancement of the ring current proton flux at energy range of ∼10–50 keV, while they disappeared at the rapid decrease of the electron density. From these results, we conclude that the boundaries of the localized IPAs and EMIC waves were determined by the overlap region of energetic proton enhancement and the plasmasphere. This overlap of ring‐current protons and plasmasphere is a favorable condition for the pitch‐angle scattering of protons by the EMIC waves. Characteristic magnetic and electric field variations with the IPAs were not observed by the satellite, indicating that the IPAs were not accompanied by field‐aligned currents comparable to that of oval auroral arcs. Plain Language Summary: Isolated proton auroras (IPAs) appearing at subauroral latitudes (∼55–65°) are generated by energetic protons precipitating from the Earth's magnetosphere, possibly through interaction with plasma waves, that is, electromagnetic ion cyclotron (EMIC) waves. An IPA indicates the spatial and temporal variation of wave‐particle interaction regions in the magnetosphere. EMIC waves are expected to contribute to the rapid loss of radiation‐belt particles into the atmosphere and affect human activities in space. In this study, we report unique multi‐event analysis of simultaneous observations of IPAs and their source regions, using all‐sky imagers at subauroral latitudes and the Van Allen Probes on 22 April, 7 September, and 22 March 2018. When the satellite footprint passed over the IPAs, locally generated EMIC waves were observed in all events. The IPAs and EMIC waves had comparable narrow widths in the latitudinal direction. These results indicate that the IPAs were caused by the EMIC waves. The appearance and disappearance of the EMIC waves were correlated with the rapid enhancement of energetic proton flux and the rapid decrease of the local electron density, respectively. We conclude that the boundaries of the localized IPAs and EMIC waves were determined by the overlap region of energetic proton enhancement and the plasmasphere. Key Points: Three ground‐satellite conjugate observations of isolated proton auroras (IPAs) and their magnetospheric source regions are reportedVan Allen Probes observed electromagnetic ion cyclotron (EMIC) waves which had radial ranges corresponding to latitudinal widths of IPAs in the ionosphere in all eventsWe conclude that the IPAs and EMIC waves are excited in the region where enhanced ring current flux overlapped with stable plasmasphere [ABSTRACT FROM AUTHOR]

We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (26 August 2018) in solar cycle 24. The underlying coronal mass ejection (CME) originating from a quiescent filament region becomes a 440 km/s magnetic cloud (MC) at 1 au after ∼5 days. The prolonged CME acceleration (for ∼24 hr) coincides with the time profiles of the post‐eruption arcade intensity and reconnected flux. Chen et al. (2019, https://doi.org/10.3847/1538-4357/ab3f36) obtain a lower speed since they assumed that the CME does not accelerate after ∼12 hr. The presence of multiple coronal holes near the filament channel and the high‐speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high‐inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase (prominence material) in the second half of the MC. Simulations using the Comprehensive Inner Magnetosphere‐Ionosphere model show that a higher ring current energy results from larger dynamic pressure (density) in MCs. Furthermore, the Dst index is highly correlated with the main‐phase time integral of the ring current injection that includes density, consistent with the simulations. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward IP magnetic field. We conclude that the high intensity of the storm results from the prolonged CME acceleration, complex rotation of the CME flux rope, and the high density in the 1‐au MC. Plain Language Summary: Powerful coronal mass ejections (CMEs) are responsible for very intense geomagnetic storms due to the out of the ecliptic component of the magnetic field in the CME flux rope or in the sheath if shock‐driving (Gosling, 1993, https://doi.org/10.1029/93ja01896). The 26 August 2018 storm was very intense, but the CME was inconspicuous and weak near the Sun. However, over an extended period of time the CME accelerated slowly and picked up adequate speed to cause an intense storm. Due to the presence of coronal holes near the eruption region, the CME rotated in such a way that the CME magnetic field and Earth's magnetic field can efficiently couple to transfer energy into the magnetosphere to cause the geomagnetic storm. The energy transfer is expedited by the presence of dense material deep inside the CME. Key Points: A coronal mass ejection characterized by prolonged acceleration, rotation, and high‐density content results in the intense geomagnetic stormSimulations with a kinetic code confirm that the ring current injection involves both solar wind dynamic pressure and electric fieldEmpirical formulas for predicting Dst based on solar wind electric field work when the magnetic cloud has no high‐density enhancement [ABSTRACT FROM AUTHOR]

Ring-current maps give a direct pictorial representation of molecular aromaticity. They can be computed at levels ranging from empirical to full ab initio and DFT. For benzenoid hydrocarbons, Hückel–London (HL) theory gives a remarkably good qualitative picture of overall current patterns, and a useful basis for their interpretation. This paper describes an implemention of Aihara’s algorithm for computing HL currents for a benzenoid (for example) by partitioning total current into its constituent cycle currents. The Aihara approach can be used as an alternative way of calculating Hückel–London current maps, but more significantly as a tool for analysing other empirical models of induced current based on conjugated circuits. We outline an application where examination of cycle contributions to HL total current led to a simple graph-theoretical approach for cycle currents, which gives a better approximation to the HL currents for Kekulean benzenoids than any of the existing conjugated-circuit models, and unlike these models it also gives predictions of the HL currents in non-Kekulean benzenoids that are of similar quality.

Since the moon’s revolution cycle is exactly the same as its rotation cycle, we can only see the moon always facing Earth in the same direction. Based on the clean particle radiation environment of the moon, a neutral atomic telemetry base station could be established on the lunar surface facing Earth to realize long-term continuous geomagnetic activity monitoring. Using the 20°×20° field of view, the 0.5°×0.5° angle resolution, and the ~0.17 cm²sr geometric factor, a two-dimensional ENA imager is being designed. The magnetospheric ring current simulation at a 4–20 keV energy channel for a medium geomagnetic storm (Kp=5) shows the following: 1) at ~60 Rᴇ (Rᴇ is the Earth radius), the imager can collect 10⁴ ENA events for 3 min to meet the statistical requirements for 2D coded imaging data inversion, so as to meet requirements for the analysis of the substorm ring current evolution process of magnetic storms above medium; 2) the ENA radiation loss puzzles in the magnetopause and magnetotail plasma sheet regions have been deduced and revealed using the 2-D ENA emission model. High spatial-temporal resolution ENA imaging monitoring of these two important regions will provide the measurement basis for the solar wind energy input process and generation mechanism; 3) the average sampling interval of ENA particle events is about 16 ms at the moon’s orbit; the spectral time difference for the set energy range is on the order of minutes, which can provide location information to track the trigger of geomagnetic storm particle events.

We present results of 131 geomagnetic storm simulations using the University of Michigan Space Weather Modeling Framework Geospace configuration. We compare the geomagnetic indices derived from the simulation with those observed, and use 2D cuts in the noon-midnight planes to compare the magnetopause locations with empirical models. We identify the location of the current sheet center and look at the plasma parameters to deduce tail dynamics. We show that the simulation produces geomagnetic index distributions similar to those observed, and that their relationship to the solar wind driver is similar to that observed. While the magnitudes of the Dst and polar cap potentials are close to those observed, the simulated AL index is consistently underestimated. Analysis of the magnetopause position reveals that the subsolar position agrees well with an empirical model, but that the tail flaring in the simulation is much smaller than that in the empirical model. The magnetotail and ring currents are closely correlated with the Dst index, and reveal a strong contribution of the tail current beyond 8 RE to the Dst index during the storm main phase.

Predicting the electron population of Earth's ring current during geomagnetic storms still remains a challenging task. In this work, we investigate the sensitivity of 10 keV ring current electrons to different driving processes, parameterised by the Kp index, during several moderate and intense storms. Results are validated against measurements from the Van Allen Probes satellites. Perturbing the Kp index allows us to identify the most dominant processes for moderate and intense storms respectively. We find that during moderate storms (Kp < 6) the drift velocities mostly control the behaviour of low energy electrons, while loss from wave-particle interactions is the most critical parameter for quantifying the evolution of intense storms (Kp > 6). Perturbations of the Kp index used to drive the boundary conditions at GEO and set the plasmapause location only show a minimal effect on simulation results over a limited L range. It is further shown that the flux at L ~ 3 is more sensitive to changes in the Kp index compared to higher L shells, making it a good proxy for validating the source-loss balance of a ring current model. [ABSTRACT FROM AUTHOR]

We present evidence of geomagnetic storms in Mercury's magnetosphere based on MESSENGER magnetic field observations made just before the probe impacted the planet. Our findings answer the question of whether geomagnetic storms can occur in other planetary magnetospheres. The interaction of the solar wind with Mercury's magnetosphere is known to involve flux transfer events in the dayside magnetosphere, plasmoids and flux ropes in the magnetotail, and substorm-like processes, all of which occur morphologically similar to Earth but with significant differences. The significantly weaker magnetic field, smaller magnetosphere, and much faster timescale of processes around Mercury, when compared with Earth, enable charged particles to escape its magnetosphere more efficiently through magnetopause shadowing and direct bombard of the surface. Our analysis of MESSENGER's data during a coronal mass ejection (CME) proves that, despite these substantial differences, a bifurcated ring current can form in Mercury's magnetosphere that initiates magnetic storms under strong solar wind driving. [ABSTRACT FROM AUTHOR]