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We incorporate field line curvature (FLC) scattering into a kinetic ring current model two‐way coupled with a global magnetospheric MHD model to investigate its role in SYM‐H prediction and global magnetospheric dynamics. FLC scattering reduces plasma pressure in regions where the ion gyroradius is comparable to the local FLC radius. This pressure reduction weakens magnetic tension, resulting in a more dipolar magnetic field configuration that, in turn, suppresses further FLC scattering. This self‐regulating feedback loop prevents excessive FLC scattering and mitigates the overestimation of ring current decay often found in models using empirical magnetic fields. We demonstrate that incorporating FLC scattering improves agreement with observed SYM‐H throughout the entire storm period. These findings highlight the importance of self‐consistent coupling between plasma dynamics and magnetic field configuration, offering enhanced predictive capability for space weather modeling.

This study analyzes electromagnetic power density E⋅j $\\mathbf{E}\\cdot \\mathbf{j}$ in the ring current region using MMS data and multi‐point analysis method. For the first time, we statistically examine the large‐scale distribution characteristics of E⋅j $\\left\\langle \\mathbf{E}\\cdot \\mathbf{j}\\right\\rangle $ (〈〉 $\\langle \\rangle $represents statistical results) within the magnetic equatorial plane, revealing a stably particles acceleration region E⋅j>0 $\\left\\langle \\mathbf{E}\\cdot \\mathbf{j}\\right\\rangle > 0$ on the dawn side and a dynamo region E⋅j<0 $\\left\\langle \\mathbf{E}\\cdot \\mathbf{j}\\right\\rangle < 0$ on the dusk side. Meanwhile, the corresponding distribution of current density and net charge density are also calculated. In the predawn sector near the acceleration region, a significant accumulation of net negative charges was observed. The dusk‐side dynamo region coincides with the net positive charge accumulation. The statistical analysis of electromagnetic power and net charge accumulation implies that the electrostatic field may play an important role in the energy variation of drifting particles, providing new insights into the evolution and dynamics of the ring current.

Magnetopause shadowing (MPS) effect could drive a concurrent dropout of radiation belt electrons and ring current protons. However, its relative role in the dropout of both plasma populations has not been well quantified. In this work, we study the simultaneous dropout of MeV electrons and 100s keV protons during an intense geomagnetic storm in May 2017. A radial diffusion model with an event‐specific last closed drift shell is used to simulate the MPS loss of both populations. The model well captures the fast shadowing loss of both populations at L* > 4.6, while the loss at L* < 4.6, possibly due to the electromagnetic ion cyclotron wave scattering, is not captured. The observed butterfly pitch angle distributions of electron fluxes in the initial loss phase are well reproduced by the model. The initial proton losses at low pitch angles are underestimated, potentially also contributed by other mechanisms such as field line curvature scattering. Plain Language Summary Magnetopause shadowing, due to the solar wind compression of the magnetopause combined with outward radial diffusion driven by ultra low frequency waves, is known to be one of the major loss mechanisms for both radiation belt electrons and ring current protons. However, the role of MPS in driving the simultaneous dropout of both populations has not been well quantified. In this study, for the first time, we quantitatively model the fast shadowing loss of radiation belt electrons and ring current protons during a geomagnetic storm event using a radial diffusion model with event‐specific inputs. The results indicate that MPS can efficiently capture the concurrent fast depletion of both populations at high L*. Key Points A radial diffusion model with event‐specific last closed drift shell is used to simulate the concurrent dropout of electrons and protons due to magnetopause shadowing The model captures the fast shadowing loss of both populations at high L* but not the loss at low L* possibly from electromagnetic ion cyclotron wave scattering The model reproduces the butterfly PAD of electrons in the initial loss phase but underestimates the loss of protons at low pitch angles

Using the Arase and Van Allen Probes satellite observations, we investigate the nonlinear electromagnetic ion cyclotron (EMIC) rising‐tone (RT) emissions with an increase of the solar wind dynamic pressure in the dayside magnetosphere. We find that EMIC RT emissions are accompanied by the extended dayside uniform zone (DUZ) over |MLAT| < 25° due to the dayside magnetospheric compression by an increase in Pdyn. Using the observed plasma and magnetic field data, we modeled the threshold amplitude for the nonlinear EMIC waves and compared it with the observation. The small gradient of the ambient magnetic field strongly contributes to the reduction in the threshold amplitude of nonlinear wave growth compared to other parameters. When the threshold amplitude falls to comparable level of pre‐existing EMIC waves, EMIC RT emissions are immediately triggered, suggesting direct evidence that the DUZ is the preferred condition to cause the nonlinear EMIC RT emission in the dayside magnetosphere. Plain Language Summary Electromagnetic ion cyclotron (EMIC) waves play an important role in controlling the dynamics of charged particles in the inner magnetosphere. Especially, nonlinear EMIC rising‐tone (RT) emissions can cause the rapid loss of relativistic electrons and ring current ions. Here, we present direct evidence demonstrating that the distortion of the dayside magnetic field causes nonlinear EMIC RT emission in response to the intensification of the solar wind dynamic pressure. Remarkably, these nonlinear EMIC waves are generated through a reduction in the threshold wave amplitudes by the distortion of the magnetic fields, even in the absence of any significant change in the pre‐existing EMIC wave amplitude. The present result provides new insights into a triggering process of nonlinear plasma waves in the magnetosphere. Key Points Electromagnetic ion cyclotron (EMIC) waves with rising‐tone (RT) elements were observed in the dayside magnetosphere during an increase in the solar wind dynamic pressure Increasing solar wind dynamic pressure extends the dayside uniform zone of the magnetic field to higher magnetic latitudes The uniform zone leads to the reduction of the nonlinear threshold wave amplitude, which triggers nonlinear EMIC RT emissions

The terrestrial ring current consists of particles with energy from several keV to 100 s of keV, and its enhancement will result in magnetic field depression, known as geomagnetic storms. The ring current is mainly composed of H+, O+, He+, and electrons, and there has been a longstanding debate regarding their relative contributions. In this study, we employed a multi‐output convolutional neural network to predict the storm‐time ring current plasma pressures of these particles. Taking solar wind parameters, interplanetary magnetic field (IMF) data, and geomagnetic indices with a time history of 3 days as input parameters, the model shows good performances for electron plasma pressure, H+ plasma pressure, He+ plasma pressure, and O+ plasma pressure in both quiet‐time and storm‐time periods, with high correlation coefficients and small root mean square errors between the measured and the predicted values. Our model successfully captures ring current enhancement during the storm main phase and species‐dependent decay during the recovery phase. Moreover, the model's ability to predict plasma pressures of different species simultaneously facilitates a comparative analysis of their respective contributions to the ring current. The storm event where our model was applied demonstrates that during the storm, the contribution of H+ decreases but still dominates, while the contribution of O+ increases dramatically, and electrons and He+ also play roles in some localized regions. The application of this model is in line with previous observations and simulations, which can be utilized for quantitative analysis of storm‐time ring current dynamics.

Based on the predictions of global 3D hybrid simulations, we present a new transport/acceleration path for escaped O+ ions in the upstream solar wind region resulting from the impact of a particular IMF tangential discontinuity (TD) with negative (positive) IMF Bz on the discontinuity's anti‐sunward (sunward) side. For O+ ions escaping to the duskside magnetosheath and with gyro‐radii larger than the TD thickness, when they encounter the TD, they can first go sunward into the upstream solar wind. They then gyrate clockwise to the pre‐noon side and get accelerated within the solar wind region and circulate back to the dawnside magnetosphere. These ions may be accelerated to well within the ring current energy range depending on the solar wind electric field strength. This new transport/acceleration path can bring some of the escaped ions into the inner magnetosphere, thus providing a new mechanism for generating an O+ ring current population. Plain Language Summary O+ ions in the magnetosphere only come from the Earth's ionosphere. For O+ ions escaping the magnetosphere, scientists have been treating them as being lost. Using simulations that can describe the O+ ion's kinetic dynamics, we find that, due to the impact of a particular solar wind structure, some escaped O+ ions can circulate back to the magnetosphere via a transport path in the upstream solar wind region and some of them can even enter the inner magnetosphere. Additionally, they are also energized by solar wind electric field and thus can contribute to the ring current population. Therefore, this study shows a new journey of escaped O+ ions. Key Points First global 3D hybrid simulations to investigate the fate of O+ ions after escaping the dayside magnetosphere New transport/acceleration path for escaped O+ ions in upstream solar wind region after impact of an IMF tangential discontinuity New transport/acceleration path brings some of escaped O+ ions back to the inner magnetosphere, contributing to O+ ring current pressure

The properties of organic molecules can be influenced by magnetic fields, and these magnetic field effects are diverse. They range from inducing nuclear Zeeman splitting for structural determination in NMR spectroscopy to polaron Zeeman splitting organic spintronics and organic magnetoresistance. A pervasive magnetic field effect on an aromatic molecule is the aromatic ring current, which can be thought of as an induction of a circular current of π-electrons upon the application of a magnetic field perpendicular to the π-system of the molecule. While in NMR spectroscopy the effects of ring currents on the chemical shifts of nearby protons are relatively well understood, and even predictable, the consequences of these modified electronic states on the spectroscopy of molecules has remained unknown. In this work, we find that photophysical properties of model phthalocyanine compounds and their aggregates display clear magnetic field dependences up to 25 T, with the aggregates showing more drastic magnetic field sensitivities depending on the intermolecular interactions with the amplification of ring currents in stacked aggregates. These observations are consistent with ring currents measured in NMR spectroscopy and simulated in time-dependent density functional theory calculations of magnetic field-dependent phthalocyanine monomer and dimer absorption spectra. We propose that ring currents in organic semiconductors, which commonly comprise aromatic moieties, may present new opportunities for the understanding and exploitation of combined optical, electronic, and magnetic properties.

One of the most intense geomagnetic storms of recent times occurred on 10–11 May 2024. With a peak negative excursion of Sym‐H below −500 nT, this storm is the second largest of the space era. Solar wind energy transferred through radiation and mass coupling affected the entire Geospace. Our study revealed that the dayside magnetopause was compressed below the geostationary orbit (6.6 RE) for continuously ∼6 hr due to strong Solar Wind Dynamic Pressure (SWDP). Tremendous compression pushed the bow‐shock also to below the geostationary orbit for a few minutes. Magnetohydrodynamic models suggest that the magnetopause location could be as low as 3.3RE. We show that a unique combination of high SWDP (≥15 nPa) with an intense eastward interplanetary electric field (IEFY ≥ 2.5 mV/m) within a super‐dense Interplanetary Coronal Mass Ejection lasted for 409 min–is the key factor that led to the strong ring current at much closer to the Earth causing such an intense storm. Severe electrodynamic disturbances led to a strong positive ionospheric storm with more than 100% increase in dayside ionospheric Total Electron Content (TEC), affecting GPS positioning/navigation. Further, an HF radio blackout was found to occur in the 2–12 MHz frequency band due to strong D‐ and E‐region ionization resulting from a solar flare prior to this storm.

Simultaneous observations of whistler‐mode chorus and magnetosonic (MS) waves are reported within a magnetic peak in the inner magnetosphere for the first time. During the magnetic peak, Van Allen Probe A observes flux enhancements of both ring current electrons and relativistic electrons, while medium‐energy proton fluxes are reduced but high‐energy proton fluxes are raised. Those flux variations of ring current particles are almost concentrated in the perpendicular direction of the background magnetic field, leading to enhancements of the electron temperature anisotropy and a positive gradient of proton velocity distributions. The calculated linear growth rates show that unstable electrons with temperature anisotropic instabilities and unstable protons with ring distribution during the magnetic peak structure can provide free energy for the excitation of whistler‐mode chorus and MS waves, respectively. Our findings suggest that injected particles encountering the magnetic peak structure may form more complex unstable electron and ion distributions driving multiple instabilities simultaneously. Plain Language Summary Recently, dipolarizing flux bundles have also been observed in the inner magnetosphere. These magnetic field structures are usually accompanied by dispersion of particle energies and pitch angles, resulting in complex and unstable particle distributions during magnetic structures, which may provide free energy for wave excitation. Previous observed waves during magnetic structures belong to single instability (electron type or proton type), rarely taking into account waves driven by both proton and electron instabilities. In this letter, simultaneous observations of chorus and magnetosonic (MS) waves are reported during a magnetic peak in the inner magnetosphere for the first time. Our results show that the complex distribution in the velocity phase space of ring current electrons and protons during the magnetic peak in the inner magnetosphere has the potential to simultaneously trigger chorus and MS waves. Key Points Whistler‐mode chorus and fast magnetosonic (MS) waves are simultaneously observed during the magnetic peak in the inner magnetosphere Enhancements of ring current particle instabilities during the magnetic peak cause the excitation of whistler‐mode chorus and MS waves Our results contribute to understanding the evolution of injected electrons and protons encountering the magnetic peak

One of the definitions of space weather describes it as the time-varying space environment that may be hazardous to technological systems in space and/or on the ground and/or endanger human health or life. The ring current has its contributions to space weather effects, both in terms of particles, ions and electrons, which constitute it, and magnetic and electric fields produced and modified by it at the ground and in space. We address the main aspects of the space weather effects from the ring current starting with brief review of ring current discovery and physical processes and the Dst-index and predictions of the ring current and storm occurrence based on it. Special attention is paid to the effects on satellites produced by the ring current electrons. The ring current is responsible for several processes in the other inner magnetosphere populations, such as the plasmasphere and radiation belts which is also described. Finally, we discuss the ring current influence on the ionosphere and the generation of geomagnetically induced currents (GIC).