Within the magnetospheres of both Earth and Jupiter, a variety of whistler-mode waves are observed, including chorus and hiss waves. At Earth, chorus waves are predominantly found outside the plasmapause, whereas hiss waves are typically confined to the plasmasphere or associated plumes. In contrast, Jupiter's magnetospheric environment is distinctive, as chorus and hiss waves frequently coexist due to the lack of a well-defined plasmapause boundary beyond the Io plasma torus. These waves play crucial roles in influencing energetic electron dynamics at both planets by facilitating the precipitation of energetic electrons into the upper atmosphere and accelerating energetic electrons to relativistic and ultrarelativistic energies.
The impact of chorus and hiss waves on energetic electron precipitation has been extensively quantified at Earth, yet their contributions at Jupiter remain largely unexplored. To address this gap, we perform a comparative analysis of energetic electron precipitation driven by whistler-mode waves at Earth and Jupiter. For Earth, we utilize recently developed empirical models of chorus and hiss waves, informed by data from the Van Allen Probes and THEMIS, covering a broad range of L-shells and Magnetic Local Times (MLTs). At Jupiter, we construct a novel statistical dataset of chorus and hiss wave properties using seven years of observations from Juno. The wave properties derived from these datasets are integrated with updated plasma and magnetic field models to compute pitch angle diffusion coefficients caused by chorus and hiss waves. A quasilinear theory-based physics model is then applied to simulate global electron precipitation driven by these waves at both planets. This comprehensive comparison quantitatively evaluates the roles of chorus and hiss waves in energetic electron precipitation on a global scale at Earth and Jupiter. Our results provide new insights into the dynamic processes governing magnetosphere-atmosphere coupling at these planets, providing broader implications for understanding similar processes at other magnetized planets within the solar system and beyond.
How to cite: Li, W., Ma, Q., and Shen, X.: Energetic Electron Precipitation Driven by Whistler-Mode Waves: A Comparative Study at Earth and Jupiter, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3761, https://doi.org/10.5194/egusphere-egu25-3761, 2025.
We investigate the plasma mass transport process known as interchange instability using data analysis and modeling. Interchange instabilities are spatially small but ubiquitous flows of hot ambient plasma into the cold Enceladus torus, resembling Rayleigh-Taylor instabilities within Saturn's inner magnetosphere. Although evidenced with Cassini spacecraft observations, their role in plasma transport and causal relationship with large-scale current-sheet collapse injection processes is not well understood.
We offer a unifying review of interchange injections seen in past statistical surveys [Azari et al., 2018; Chen & Hill, 2008; Kennelly et al., 2013; Lai et al., 2016] by explaining measurements from the Radio and Plasma Science (RPWS) instrument, and comparing wave-types and properties against characteristics seen co-occurring in the particle sensors (ion and electron in MIMI and CAPS), and magnetometer (MAG). Additionally, we investigate the conditions within the inner magnetosphere of Saturn using the Hot Electron and Ion Drift Integrator (HEIDI), a drift kinetic model that solves the gyro- and bounce-averaged Boltzmann equation for the energetic plasma population [Liemohn et al., 2001, 2006; Ilie et al., 2012, 2013; Liu and Ilie, 2021]. Originally designed for Earth, we will present steps taken towards adapting this model for Saturn and reproducing interchange instability injections as a source/loss term for the environment.
How to cite: Hathaway, E., Liemohn, M., Azari, A., Silva, P., Ilie, R., and Hospodarsky, G.: Transport in Saturn's Inner Magnetosphere: Using Particle and Wave Data to Study Rayleigh-Taylor like Interchange Instability Injection Events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20589, https://doi.org/10.5194/egusphere-egu25-20589, 2025.
We report multiple series of zebra stripes (aka drift echoes) of relativistic electrons, measured by the REPTile‐2 (Relativistic Electron and Proton Telescope integrated little experiment‐2) Instrument onboard CIRBE (Colorado Inner Radiation Belt Experiment) CubeSat, which operated in a highly inclined low Earth orbit from April of 2023 to October of 2024. Thanks to the high energy resolution measurements, zebra stripes of 0.25–1.4 MeV electrons, appearing as structured bands in energy spectrograms, across the entire inner belt and part of the outer belt (L=1.18 to >3) have been frequently observed, from quiet times, moderate times, to active times. Through test particle simulations, we show that a prompt electric field with a peak amplitude ∼5 mV/m in near‐Earth space can lead such zebra stripes of relativistic electrons. Azimuthal inhomogeneity of electron distribution caused by the prompt electric field modulates the electron energy spectrum by energy‐dependent drift phases to form the zebra stripes. Though zebra stripes are observed in both belts, they tend to last longer and appear more frequently in the inner belt. Zebra stripes in the outer belt tend to have a shorter lifetime due to more perturbations, resulting in energy and pitch angle diffusion of the electrons, which diminish the structure. This study demonstrates the important role of electric fields, the exact causes of which are still under investigation, in the dynamics of relativistic electrons and contributes to the understanding of the mechanisms creating and diminishing zebra stripes.
How to cite: Li, X., Mei, Y., O'Brien, D., and Xiang, Z.: On the “Zebra Stripes” of Relativistic Electrons Unveiled by CIRBE/REPTile‐2 Measurements and Test Particle Simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2189, https://doi.org/10.5194/egusphere-egu25-2189, 2025.
Since the beginning of the space age, radiation belts have been a subject of great interest to scientists and space industry stakeholders due to their highly energetic and dynamic nature, which poses hazards to both spacecraft and humans. In particular, during strong geomagnetic activity, the particle fluxes in the outer electron radiation belt can be enhanced a thousand times compared to quiet times. Therefore, it is crucial to understand their dynamics along with the physical processes behind it.
Physical models simulate the dynamics of magnetically trapped particles in the radiation belts based on the Fokker-Planck formalism with different levels of representation. The Salammbô 3D code has proven its effectiveness in forecasting and nowcasting radiation belt dynamics as well as assessing associated risks. To expand the modeled energy range and enable studies of internal charging, it exists the Salammbô 4D code. This drift-resolved code breaks the symmetry of drift motion and incorporates the effects of magnetospheric electric fields into the dynamic.
We present advancements to Salammbô 4D through upgrades to key physical processes. These upgrades enable a more realistic representation of low-energy particle dynamics in inner magnetosphere modeling. The improvements include several key advancements. First, the modeling of convective particle transport has been refined by incorporating a realistic electric field model. Second, a more accurate description of magnetopause shadowing has been introduced. Finally, an event-based and Magnetic Local Time (MLT)-dependent wave-particle interaction modeling has been implemented.
How to cite: Kiraz, R., Dahmen, N., Maget, V., and Lavraud, B.: Improvements in the 4D drift-resolved radiation belt code Salammbô 4D., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10451, https://doi.org/10.5194/egusphere-egu25-10451, 2025.
Military very low frequency (VLF) transmitters represent a significant anthropogenic source of electromagnetic waves. Their signals can travel considerable distances within the Earth-ionosphere waveguide, but they also penetrate the ionosphere and propagate through the inner magnetosphere. There, they can be readily observed by spacecraft instruments with sufficient frequency resolution and range, and they can precipitate energetic electrons trapped in the Van Allen radiation belts.
We use 23 years of measurements from the WHISPER instruments on board the four Cluster spacecraft, operating at frequencies up to 80 kHz, to investigate the observed intensities of VLF transmitter signals. The signals are about an order of magnitude more intense at night than during the day, and they appear to be confined within the plasmasphere. The unique latitudinal coverage of the Cluster spacecraft measurements allows us to investigate frequency cut-offs in the transmitter spectra. These cut-offs are mostly consistent with nonducted propagation, though occasional partial ducting seems necessary to explain signals spanning otherwise inaccessible regions. The observed intensity patterns are compared with the calculations of Starks et al. (2020), demonstrating an overall agreement in the pattern, but with the observed wave intensities by a factor of about 2-3 lower than predicted.
How to cite: Nemec, F., Santolik, O., and Albert, J. M.: Spacecraft observations of VLF transmitter signals and their propagation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4831, https://doi.org/10.5194/egusphere-egu25-4831, 2025.
Exohiss waves are a type of structureless whistler‐mode waves that exist in the low density plasmatrough outside the plasmapause and may potentially perturb the motions of electrons in the radiation belt and ring current. Using data from Van Allen Probe A, we analyze the distribution of magnetic power spectral density (PSD) of exohiss waves in different magnetic local time (MLT) and L‐shell regions near the geomagnetic equator. The results reveal that the peak magnetic PSD of exohiss waves is the weakest at MLT = 0–6 and the strongest at MLT = 12–18. The magnetic PSDs of exohiss waves are much lower than those of chorus and hiss waves except for the MLT = 12–18 sector. In addition, we calculated the quasi‐linear bounce‐ averaged pitch angle and momentum diffusion coefficients (⟨Dαα⟩ and ⟨Dpp⟩) of electrons caused by exohiss waves. The diffusion coefficients are then compared with those caused by chorus and hiss waves. The peak ⟨Dαα⟩ of electrons driven by exohiss waves becomes stronger as L‐shell increases at all MLTs and is the greatest on the dayside, especially in the sector of MLT = 12–18. Exohiss waves have more significant effect on the loss of radiation belt electrons with specific energy levels related to MLT and L‐shell region compared to chorus and hiss waves. On the other hand, ⟨Dpp⟩ of electrons caused by exohiss waves is very small, which illustrates that exohiss waves have almost no acceleration effect on electrons.
How to cite: Tang, R., Li, H., Ouyang, Z., Zou, W., and Feng, B.: Statistical Properties of Exohiss Waves and Associated Scattering Losses of Radiation Belt Electrons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14811, https://doi.org/10.5194/egusphere-egu25-14811, 2025.
The rising tone chorus elements show a fine structure consisting of multiple subpackets with varying amplitudes and durations. Using data from Van Allen Probe A (2012 −2019) and an automated ”isolation” algorithm, we identify 382594 chorus elements and classify them as isolated or overlapped. We find that during active conditions, these two types show opposite day-night asymmetry distribution in magnetic local time (MLT). The isolated chorus elements are observed more on the nightside and dawnside, corresponding to the shorter repetition time. Conversely, overlapped chorus elements dominate the dayside due to the smaller frequency difference between the overlapping segments, facilitating wave superposition inside packets. Additionally, we compare the properties of both types. We find the packets of isolated waves tend to exhibit longer duration and larger amplitude, and show good agreement with the nonlinear theory of chorus wave growth. However, the packets of overlapped waves are shorter and exhibit small frequency and amplitude differences confined in a narrow range, suggesting a contribution from wave superposition effects.
How to cite: He, J., Chen, L., and Xia, Z.: Statistical Analysis of Subpacket Structure in Isolated and Overlapping Chorus Elements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13113, https://doi.org/10.5194/egusphere-egu25-13113, 2025.
Debates have been lasting for decades on how to characterize resonant interactions between magnetospheric electrons and plasma waves. Practically, quasilinear theory is applied to model the evolution of electron populations. Under this framework, electron dynamics are approximated as diffusion processes described by Fokker-Planck equation, which are governed by the time-averaged wave power spectrum only. For wave modes such as chorus, fine structures including discreteness and frequency chirping are left out. These structures, together with the intense, coherent nature of chorus waves, could possibly induce nonlinear electron motions which are rapid in phase space. Quantifying the deviation from quasilinear theory is important for accurate space weather forecasts.
Self-consistent PIC simulations can generate chorus waves with all key features realistic. By performing test-particle simulations with PIC-originated chorus waves, we track an ensemble of electrons for several bounce periods to make detailed comparisons between the evolution of its distribution function and quasilinear theory. Varying L-shell and wave packet spacings in PIC simulations shows the sensitivity of our results.
How to cite: An, Z. and Tao, X.: Long-Term Radiation Belt Electron Dynamics Driven by Chorus Waves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15132, https://doi.org/10.5194/egusphere-egu25-15132, 2025.
High-energy particles in geosynchronous orbit (GEO) present significant hazards to astronauts and artificial satellites, particularly during extreme geomagnetic activity conditions. In the present study, based on observations onboard the GOES-15 (Geostationary Operational Environmental Satellites) spanning from 2011 to 2019 as well as the historical values of solar wind and geomagnetic activity indices, an artificial neural network (ANN) model was established to predict the temporal evolution of the GEO sub-relativistic and relativistic (>0.8 MeV and >2 MeV) electron fluxes one day in advance. By adding the last-orbital observations of electron flux in each of all 24 different MLTs (magnetic local times) and its two MLT-adjacent values into inputs, the current model can provide accurate predictions with an MLT-resolution of one hour for the first time. Moreover, it achieves the best performance in comparison with previous methods, with overall root-mean-square-errors (RMSEs) of 0.276 and 0.311, prediction-efficiencies (PEs) of 0.863 and 0.844, and Pearson-correlation-coefficients (CCs) of 0.930 and 0.921 for >0.8 MeV and >2 MeV electrons, respectively. More than 99% of the samples exhibit an observation-prediction difference of less than one order of magnitude, while over 90% demonstrate a difference of less than 0.5 order. Further analysis revealed that it can precisely track the global variations of the electron flux during both quiet times and active conditions. The present model would be an important supplement for examining the temporospatial variations of inner magnetospheric particles and helping to establish a warning mechanism for space weather disaster events.
How to cite: Zou, Z., Zhang, L., and Zuo, P.: Global Prediction of Sub-relativistic and Relativistic Electron Fluxes in the Geosynchronous Orbit Using Artificial Neural Networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16375, https://doi.org/10.5194/egusphere-egu25-16375, 2025.
The inner magnetosphere hosts distinct features such as the plasmasphere and its plasmapause boundary that interact between the denser, inner layer of the magnetosphere and the outer region. Due to the complexity of magnetospheric dynamics, scientists often rely on models of the inner magnetospheric electric field (IMEF) and electric potential for better understanding. However, existing models struggle to accurately reproduce inner magnetosphere electrodynamics, especially in times of high geomagnetic activity. Here, we present a physio-temporal analysis of the first Machine Learning Inner Magnetospheric Electric Field (ML-IMEF) model with the aim to advance the state of physics-based modeling of the magnetosphere through improved accuracy and predictive capabilities. ML-IMEF is a multi-layer deep neural network trained on electric field data from multiple instruments onboard NASA’s Magnetospheric Multiscale (MMS) mission where we train our model with the time history of location data and geomagnetic indices. The result of the IMEF is a global, dynamic and time-dependent model of the IMEF where we resolve the electric potential contours through the solving an inverse problem. We evaluate the modeled electric field and potential during varying geomagnetic storms, including the May 2024 Gannon Storm, and compare the plasmapause boundary with other models, such as the Moldwin et al. (2002) empirical plasmapause model. Furthermore, we explore magnetospheric characteristics of our model in relation to meso-scale electric field features, such as electric potential patterns and last closed equipotential (LCE) lines.
How to cite: Isola, B., Argall, M., and Torbert, R.: Plasmapause Observations from a Data-Driven Model of the Magnetospheric Electric Field, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-590, https://doi.org/10.5194/egusphere-egu25-590, 2025.
Due to solar wind-magnetosphere coupling, energetic electron fluxes in the outer radiation belt are profoundly influenced by enhanced solar activities. Utilizing observations from Van Allen Probes (VAPs) and low Earth orbit MetOp-02, here we report a case study of dramatic pitch-angle dependent variations of ultra-relativistic electron fluxes within one day from 19 to 20 December, 2015. We focus on two orbits of VAPs, which contains two successive interplanetary shocks in the first orbit and then storm main phase in the second orbit. Consequently, the ultra-relativistic electron fluxes exhibit around 90°-peaked distributions at L* > 5 in dayside magnetosphere right after each shock, followed by dropouts at almost all pitch angle distributions throughout the outer radiation belt. Electron phase space density (PSD) profiles show that adiabatic effects contribute to the accelerations at high pitch angles (> ~45°) and L* > 5 for both shocks while inward radial diffusion plays a dominant role at lower L* after the second shock. Additionally, pitch angle scattering loss driven by concurrent EMIC waves result in the dropouts at low pitch angles (< ~45°) after each shock. Furthermore, the precipitations in a close magnetic conjugation after the first shock provide sufficient evidence for EMIC-induced loss. Our results also show that the dropouts throughout the outer belt in the second orbit are attributed to a combination of magnetopause shadowing effect at L* > 4.5 and EMIC-driven pitch angle scattering loss at L* < 4. Our study provides direct observational evidence that combinations of multi-mechanisms, including adiabatic and non-adiabatic effects, result in the dramatic dynamics of ultra-relativistic electrons within one day.
How to cite: Wang, X., Wang, D., Cao, X., Ni, B., Drozdov, A., Zhang, X., Dou, X., and Shprits, Y.: Dynamics of Ultra-relativistic Electrons on 19 December 2015: Combinations of Adiabatic and Non-adiabatic Effects, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3270, https://doi.org/10.5194/egusphere-egu25-3270, 2025.
Plasmaspheric hiss plays an important role for the electron precipitation and the formation of slot in radiation belts. It is easy for hiss waves to resonate with and scatter energetic electrons at higher L shells, as the frequencies of hiss waves decrease with the distance away from the earth. Recent studies show the whistler-mode waves can be guided in the density irregularities, performing parallel propagation experiencing little Landau damping. Therefore, the resonance between ducted waves and energetic electrons can expand to higher latitudes, and then drive strong energetic electron scattering. In this study, we report a conjugate observation using data from Van Allen Probe A in the magnetosphere and POES satellite in the ionosphere. Through the analysis of both observation and the quantification of quasi-linear diffusion coefficients, the results show the ducted hiss can more effectively scatter the energetic electrons and drive enhanced electron flux at low ionospheric altitudes. We suggest the ducting propagation of hiss is important for electron loss process in radiation belts.
How to cite: Feng, B., Li, H., Tang, R., Zhou, M., Ouyang, Z., Wang, D., Yu, X., Xiong, Y., Chen, Z., Yuan, A., and Cheng, Y.: Energetic Electron Diffusion and Precipitation Driven by Ducted Hiss Waves in High Density Irregular Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4399, https://doi.org/10.5194/egusphere-egu25-4399, 2025.
The diffuse aurora is a natural phenomenon observed over the Earth's polar region. Compared with the nightside diffuse aurora, the brightness of the dayside diffuse aurora (0600-1800 magnetic local time (MLT)) is relatively weak, thus requiring more stringent observation conditions. Therefore, the current understanding of what causes the dayside diffuse aurora is still quite limited. Here, we present an intense morningside diffuse aurora (0600-1000 MLT) event observed on 1 January 2016 during the recovery phase of the substorm, using conjugate observations of wave and particle spectrum from the Radiation Belt Storm Probes (RBSP) and auroral emission from the Special Sensor Ultraviolet Spectrographic Imagers on the Air Force Defense Meteorological Satellite Program (DMSP/SSUSI). We perform calculations of diffusion coefficients and simulations of the electron fluxes for this event. Our results show that the chorus waves are the primary contributors to the formation of the morningside diffuse aurora, with precipitated electron energies ranging from a few keV to tens of keV. The lower band chorus shows significant pitch angle scattering efficiency for electrons with energies from 5 keV to 20 keV. The upper band chorus waves induce acceleration effects on 1 keV - 20 keV electrons. We suggest that the upper band chorus waves accelerate low-energy electrons to higher energies, enabling them to engage in the scattering process of the lower band chorus waves. Our study makes a contribution to recent research on the formation mechanisms of diffuse aurora and deepens our understanding of wave-particle interactions leading to dayside electron precipitation.
How to cite: Feng, H., Wang, D., Guo, D., Shprits, Y. Y., Han, D., Teng, S., Ni, B., Shi, R., and Zhang, Y.: Lower Band Chorus Wave Scattering Causing the Extensive Morningside Diffuse Auroral Precipitation During Active Geomagnetic Conditions: A Detailed Case Study , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4619, https://doi.org/10.5194/egusphere-egu25-4619, 2025.
Properties of power line harmonic radiation (PLHR), electromagnetic radiation produced by electric power networks, are examined. Particularly, we study how PLHR intensity depends on local time and geomagnetic activity and what are its characteristic spatial scales. We use high-resolution wave data measured by the ground-based Kannuslehto station in northern Finland, supplemented with corresponding conjugate measurements from the low-altitude DEMETER spacecraft. PLHR intensities are calculated by subtracting the background wave intensities at nearby frequencies (+/- 2 Hz). The effects of geomagnetic activity on PLHR are associated with geomagnetically induced currents (GICs) that are created at the Earth’s surface by the space weather-related events and that influence the creation of PLHR directly in the power grids. We characterize the strength of GICs using the change of the horizontal component of the geomagnetic field measured by magnetometers (IMAGE magnetometer network) located close to the Kannuslehto station. We show that PLHR is continuously detected by Kannuslehto, being more intense at odd harmonics during the day and during periods of large magnetic field changes. Data from the DEMETER spacecraft are used for selected PLHR events to estimate their characteristic spatial scales.
How to cite: Drastichova, K., Nemec, F., Manninen, J., and Raita, T.: Power line harmonic radiation observed by the Kannuslehto station and the DEMETER spacecraft, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5090, https://doi.org/10.5194/egusphere-egu25-5090, 2025.
Electromagnetic (EM) waves generated by lightning strokes in the Earth’s atmosphere are important phenomena regarding the loss of energetic electrons from the Van Allen radiation belts. During lightning-induced electron precipitation (LEP) events, these EM waves interact with trapped radiation belt electrons, decreasing their pitch angle, and causing their eventual loss in the atmosphere. LEP events in satellite data are characterized by a sudden increase in wave intensity over a wide range of frequencies, accompanied by an increase in the precipitating electron flux. We develop a semi-automatic procedure to detect LEP events in the wave and particle burst mode data measured by the DEMETER satellite between 2004 and 2010. In total, we detected more than 400 events, mostly above the U.S. East Coast. The identified events occurred mainly at L-shells between approximately 2 and 3.75, and extended up to energies of about 200 keV. We show an annual variation in VLF wave intensities and precipitating energetic electron fluxes comparable with the annual variation of lightning occurrence. Finally, we estimated total precipitating electron fluxes and wave intensities based on the average LEP properties and lightning occurrence rate, showing that the individual isolated LEP events appear to be insufficient to explain the observed summer-winter differences in the precipitating electron fluxes above the U.S. region.
How to cite: Linzmayer, V., Nemec, F., Santolik, O., and Kolmasova, I.: DEMETER Satellite Observations of Lightning-Induced Electron Precipitation Events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5096, https://doi.org/10.5194/egusphere-egu25-5096, 2025.
The ring current, a key feature of Earth's magnetosphere, is enhanced during geomagnetic storms, posing risks to spacecraft through surface charging by 10-50 keV electrons. While extensively studied, accurately modeling storm-time ring current dynamics remains challenging.
We show that existing ring current models significantly overestimate the trapped population of the Earth’s night-side electron ring current at energies between 10 and 50 keV during geomagnetic storms compared to satellite observations. Through analysis of electron drift trajectories, we identify a missing pre-midnight loss process, requiring strong diffusion to match observations. Validation of predicted electron precipitation using low-Earth orbit satellite measurements further supports our findings that strong diffusion is reached in a broad region in the pre-midnight sector.
We further discuss the physics behind this loss process, which has been neglected in previous modeling efforts. Incorporating this loss process in future models is key to accurately predicting the storm-phase electron ring current and its associated space weather hazards.
How to cite: Haas, B., Shprits, Y., Wang, D., Himmelsbach, J., and Stoll, K.: Resolving Discrepancies in Electron Ring Current Models: The Importance of a Pre-Midnight Loss Process, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5472, https://doi.org/10.5194/egusphere-egu25-5472, 2025.
The South Atlantic Anomaly (SAA) affects the particle evolution and loss processes in the inner magnetosphere. However, most existing inner magnetosphere models average the north-south loss cone to simplify precipitation calculations, neglecting the SAA's impact. Based on the Storm-Time Ring Current Model (STRIM) accounting for the SAA effect, we simulate a storm event to analyze electron precipitation in both hemispheres. Results show that electron loss near the SAA is more pronounced than other local times around L = 4. Previous averaging methods underestimated electron precipitating fluxes in the southern hemisphere while overestimating them in the northern hemisphere. Furthermore, we find that SAA significantly promotes low-energy (several keV) electron precipitation compared to high-energy (hundreds of keV) electrons. Comparisons with in-situ observations demonstrate that simulations considering the SAA effect capture both the intensity and variations of electron precipitation. This study emphasizes the necessity of including the SAA effect in models for accurately interpreting ring current electron dynamics and the north-south asymmetry of electron precipitation.
How to cite: Ma, L., Yu, Y., Yue, C., Li, Y., and Cao, J.: The effect of South Atlantic Anomaly on ring current dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5804, https://doi.org/10.5194/egusphere-egu25-5804, 2025.
Recent studies have shown that existing ring current models overestimate the electron flux of 10-50 keV during storm-time, which is due to a missing loss process operating in the pre-midnight sector. At the same time, there are several studies which suggest that wave-particle interactions with electrostatic electron cyclotron harmonic (ECH) waves or time domain structures (TDS) can efficiently scatter electrons at energies of several hundred eV to a few keV, depending on the observed wave amplitude. These resonant interactions between electrons and ECH waves or TDS have an impact on electron phase space density evolution, but typical quasi-linear studies of ring current dynamics do not currently incorporate them. Since the scattering rates due to wave-particle interactions with both ECH waves and TDS increase with increasing geomagnetic activity, they are possible candidates to explain part of the missing loss process during storm-time.
In this study, we perform a detailed analysis of the efficiency of ECH wave scattering for a wave event that occurred during the geomagnetic storm on 17 March 2013, by calculating quasi-linear bounce-averaged scattering rates. Furthermore, we estimate the diffusion coefficients due to TDS in the inner magnetosphere. The resulting lifetimes from both ECH waves and TDS are incorporated into simulations conducted using the 4-dimensional Versatile Electron Radiation Belt (VERB-4D) code. The results demonstrate that for the considered event, ECH waves can scatter electrons over a wide range of energies up to several keV, but the resulting lifetimes are too long to significantly alter the resulting pitch angle distribution. However, first results indicate that TDS are able to efficiently scatter electrons up to tens of keV, removing a substantial part of the overestimated flux in the model. This strengthens the assumption that they are a possible candidate to explain part of the missing loss process in ring current models.
How to cite: Stoll, K., Pick, L., Wang, D., Haas, B., Shen, Y., Cao, X., Ni, B., and Shprits, Y.: Electron Scattering by Electrostatic Electron Cyclotron Harmonic Waves and Time Domain Structures During Storm-Time, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7086, https://doi.org/10.5194/egusphere-egu25-7086, 2025.
Electrons in Earth’s radiation belts exhibit significant variability in both space and time during geomagnetic storms, posing potential risks to satellites and astronauts. Physics-based models aim to describe the behavior of energetic electrons in the radiation belts but often face challenges due to uncertainties and inaccuracies, especially in the initial and boundary conditions. Data assimilation addresses these limitations by integrating satellite observations with model predictions, incorporating all available information to produce a more reliable reconstruction. This study evaluates the performance of the data-assimilative 3D Versatile Electron Radiation Belt code (VERB-3D) using data from three independent satellite missions: Arase and GOES for assimilation and Van Allen Probes for validation. The datasets were carefully cleaned and normalized to ensure compatibility. The results confirm that the model accurately reproduces radiation belt dynamics, highlighting the effectiveness of data assimilation techniques for space weather research and improving our understanding of the radiation belt environment.
How to cite: García Peñaranda, M., Y. Shprits, Y., Y. Drozdov, A., Castillo Tibocha, A. M., Haas, B., Szabó-Roberts, M., Wang, D., Cervantes, S., Miyoshi, Y., Mitani, T., Takashima, T., Hori, T., Shinohara, I., Matsuoka, A., Teramoto, M., and Yamamoto, K.: Global Validation of the Data-Assimilative VERB-3D Code for the Radiation Belts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10044, https://doi.org/10.5194/egusphere-egu25-10044, 2025.
Chorus waves play a key role in the dynamics of energetic electrons in Earth's radiation belts, making it essential to understand their spatial distribution. However, data from a single spacecraft mission are often insufficient to capture the spatial and temporal variability of chorus waves. This study focuses on the statistical analysis of chorus wave observations from two distinct satellite missions: the Van Allen Probes and Arase. While the Van Allen Probes are well-established and extensively utilized dataset of wave observations, their coverage is limited to 20 degrees magnetic latitude, whereas Arase extends beyond 40 degrees. Thus, investigating the statistical properties of chorus waves is important for developing techniques to combine these two sets of observations, providing a more comprehensive spatio-temporal dataset. We perform a comparative analysis of magnetic intensity of chorus waves from both satellite missions, aiming to understand their spatial and temporal characteristics during the overlapping mission period. Preliminary results indicate that the statistical features of chorus wave intensities observed by the Van Allen Probes and Arase agree in general. However, in time-averaged observations, the Van Allen Probes yield higher values than those of Arase. These findings will help develop chorus wave models by combining the observations from these two satellite missions.
How to cite: Roy, A., Wang, D., Shprits, Y. Y., Albert, J., Drozdov, A., Santolík, O., Hanzelka, M., Feng, T., Lepage, T., Miyoshi, Y., Reeves, G. D., Kasahara, Y., Kumamoto, A., Matsuda, S., Matsuoka, A., Hori, T., Shinohara, I., Tsuchiya, F., Teramoto, M., and Yamamoto, K.: Statistical Analysis of Chorus Wave Observation from the Van Allen Probes and Arase Spacecraft, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10054, https://doi.org/10.5194/egusphere-egu25-10054, 2025.
Electron precipitation remains a dominant topic of study with confusion persisting as to whether instruments are measuring stable trapped electrons in low earth orbit, locally precipitating electrons, or electrons that will be lost over the course of a drift orbit. In this study, we present a preliminary study focusing on categorizing electrons by their precipitation mechanism (bounce loss or drift loss) or as trapped populations. Using the Electron Losses and Fields Investigation (ELFIN) Spatio-Temporal Ambiguity Resolution (STAR) CubeSat measurements developed at UCLA, we determine which keV – MeV electrons are lost and trapped within each MLT sector. The ELFIN-STAR measurements are used to determine the magnetic footprint required for particles to be lost via bounce loss and/or drift loss.
How to cite: Saikin, A., Drozdov, A., and Shprits, Y.: MLT distributions of Bounce Loss and Drift Loss cone electrons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13471, https://doi.org/10.5194/egusphere-egu25-13471, 2025.
Electromagnetic ion cyclotron (EMIC) waves are important for the loss of radiation belt electrons and ring current ions. After being excited by an instability driven by the temperature anisotropy followed by nonlinear wave-particle interactions occurring near the magnetic equator of the inner magnetosphere, EMIC waves propagate parallel along the magnetic field lines with left-handed polarization. Their wave normal angles with respect to the magnetic field increase as the waves propagate to higher latitudes. At latitudes where the wave frequency is the same as the crossover frequency, the polarization changes from left-handed to right-handed, called polarization reversal. Polarization reversal is one of the mechanisms that allow EMIC waves to propagate to the ground without being reflected in the magnetosphere, because based on the dispersion relation of the cold plasma, they could only exist in the frequency range above the cutoff frequency if they remained with the left-handed polarization. The crossover frequency at which the polarization reversal occurs depends highly on the surrounding plasma environment. To investigate the polarization reversal in the magnetosphere, conjugate observation, in which the same event is observed at different latitudes, is useful for discussing the propagation process of plasma waves and changes in the surrounding plasma environment.
In this study, we analyzed EMIC waves simultaneously observed by the Arase, Cluster and ground-based induction magnetometer at the Gakona station ( 62.39° N and 214.78° E geographic coordinates). We used the electric and magnetic field waveform data observed by the PWE-EFD and MGF onboard the Arase satellite and the magnetic field waveform data observed by STAFF onboard the C1 satellite. Also, we used the induction magnetometer data from the Gakona station. The event of interest was observed from 21:20 to 21:40 UT on July 25,2020, with the same L-value-(L=6) and MLT-(12.9 MLT). In the spectra observed by Arase located in the equatorial region (MLAT= 5°), we identified the enhancement of electromagnetic waves in the frequency range from 0.65Hz to 1.1Hz, corresponding to the proton-band EMIC waves. The same EMIC wave was observed by C1 and Gakona. At this time C1 was located away from the equator-(MLAT= -22° ). While the frequency range of the EMIC wave observed at Arase was higher than the He+ cyclotron frequency, ƒHe+ , the EMIC wave observed at C1 appeared in the spectra close to ƒHe+. Considering the cold plasma dispersion relation, it was suggested that polarization reversal may have occurred during the wave propagation from the equatorial region at Arase to the higher latitude at C1. We have also performed the Singular Value Decomposition (SVD) method(Santolik et al. 2003) for each satellite data, which allows us to derive polarization properties. As a result, it was confirmed that the polarization in C1 changed from linear polarization to right-handed polarization below a specific frequency. With these results, it is observationally clear that the conditions for the EMIC wave propagation to the ground are satisfied. We also discussed the surrounding plasma environment and the generation process of the observed EMIC wave.
How to cite: Miyashita, S., Katoh, Y., Kasaba, Y., Tuchiya, F., Kumamoto, A., Kasahara, Y., Matsuda, S., Miyoshi, Y., Hori, T., Shinbori, A., Shiokawa, K., Oyama, S., Matsuoka, A., Teramoto, M., Santolík, O., and Grison, B.: Case study of propagation characteristics of EMIC wave using multipoint observation by Arase, Cluster, and Ground Station, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14668, https://doi.org/10.5194/egusphere-egu25-14668, 2025.
Using data from the Swarm and Magnetospheric Multiscale (MMS) missions collected between September 1, 2015, and May 1, 2024, we present a direct comparison of field-aligned currents (FACs) from the ring current (RC) region and polar regions for the first time through statistical analysis. Our analysis examines the response of FACs to different upstream interplanetary magnetic field (IMF) directions and solar wind (SW) flow velocity directions, the FAC distribution corresponding to various AE and SYMH indices, and the overall trends of FAC current directions in both the polar and RC regions. Leveraging the extensive coverage provided by Swarm data, we conducted a seasonal analysis of how polar FACs respond to IMF BX, BY, BZ, as well as SW VZ. The results show that the direction of SW flow velocity has a weak effect on polar FACs, while the IMF plays a significant role. The average results smooth out the seasonal differences indicate that polar FACs only show differences in response to the varying directions of BZ. In contrast, RC region FACs are also significantly influenced by SW VZ. Both increases in the AE and SYMH indices are associated with enhanced FAC current densities, with polar FACs showing a better correlation with the AE index. Overall, the flow direction trends of FACs < 70° MLAT in both the polar and RC regions are similar, with stronger current densities observed in the Northern Hemisphere. However, current densities derived from simple coefficient calculations in the polar and RC regions do not directly match, showing a significant order-of-magnitude difference. Additionally, a marked hemispheric difference in FAC direction is observed in the 07:30-10:00 MLT, 60°-70° MLAT region in both the polar and RC regions.
How to cite: Tan, X., Dunlop, M., Yang, J., Zhang, C., Russell, C., and Lühr, H.: Trends in Field-Aligned Currents from the Polar Regions to the Ring Current Region: 10 Years of Observations from Swarm and MMS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16158, https://doi.org/10.5194/egusphere-egu25-16158, 2025.
Exohiss serves as a typical imprint of the outward energy release from plasmaspheric hiss. The distribution of exohiss under the effect of Landau damping has not been thoroughly evaluate. On the basis of observations from the Van Allen Probes on 17 February 2014, we performed two‐dimensional ray tracing simulations to model the evolution of hiss waves propagating from the geomagnetic equator in plasmasphere. The results show that the hiss wave power decreases rapidly as the waves enter the plasmatrough under the enhanced Landau damping effect of hot electrons. Furthermore, we perform a statistical analysis of the simulation results from multiple rays and obtain the radial, latitudinal, and frequency distributions of the exohiss wave power. The modeled distribution characteristics of exohiss align well with observations, suggesting that Landau damping is crucial in shaping the morphology of exohiss in the inner magnetosphere.
How to cite: He, Z.: Radial and Latitudinal Distributions of the Exohiss Under the Effect of Landau Damping, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21022, https://doi.org/10.5194/egusphere-egu25-21022, 2025.
Sudden changes in the ground magnetic field, driven by geomagnetic activity, can ultimately generate geomagnetically induced currents (GICs), which can have a significant impact on artificial technology systems. High rates of change of the horizontal geomagnetic field (dH/dt) can be used as a substitute for the strength of GICs. It has been suggested that GIC signals in the nightside local time sectors can indirectly be driven by field-aligned currents (FACs) flowing into the ionosphere, which themselves can be generated during arrival of bursty bulk flows (BBFs) into the nightside transition region (through an improved substorm current wedge, SCW). We extend the analysis of the January 7, 2015 substorm by utilizing multi-point observation techniques from ground stations and satellites. We combine the data from the magnetosphere and ionosphere with the behaviour of the dH/dt component obtained from ground stations. Our results confirm that Region 1 (R1) type FACs driven by the BBF arrivals form a loop with the westward auroral electrojet currents (AEJs), an important driving factor for ground GICs. We also briefly show the role of corresponding ULF wave signals during the event. This further explains how BBFs affect ground GICs, which will help to understand the coupling between ionospheric current systems and ground currents.
How to cite: Zhang, C., Malcolm, D., Yang, J., Tan, X., Octav, M., Adrian, B., Xiong, C., Dong, X., Wei, D., Vlad, C., and Guram, K.: Joint Analysis with Swarm and Ground Stations: Ionospheric Current System and Geomagnetically Induced Currents, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5572, https://doi.org/10.5194/egusphere-egu25-5572, 2025.
Plasmapause surface waves (PSWs) near the plasmapause boundary are regarded to be the magnetospheric source of ionospheric auroral giant undulations (GUs) located at the equatorward boundary of diffuse aurora. However, the observational evidence of wave-particle interaction connecting PSWs and GUs is absent. In this letter, we demonstrate GUs are driven by pitch-angle scattering of time domain structures modulated by the PSWs, based on the conjugated ionospheric and magnetospheric observations. Specifically, ionospheric GUs are lighted by the pitch-angle scattering of < 1 keV thermal electron and ions and energetic ions with energy up to dozens of keV near the plasmapause. Further, the total fluxes during one PSW period and energy of scattered electron and ions determine the size and luminosity of GUs. Our research provides observational evidence that PSWs cause periodic particle precipitation via modulating the time domain structures rather than the previously predicted chorus or electron cyclotron harmonic (ECH) waves.
How to cite: Yi-Jia, Z.: Giant Undulations driven by Pitch-Angle Scattering of Time Domain Structures modulated by Plasmapause Surface Wave, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7899, https://doi.org/10.5194/egusphere-egu25-7899, 2025.
Energetic electrons in Earth’s radiation belts emit cyclo-synchrotron radiation as they are deflected by the planet’s magnetic field. These emissions provide valuable insights into the spatial and energy distributions of trapped electrons and their dynamic behavior over time. However, because this radiation occurs at frequencies below 10 MHz, it is blocked by the ionosphere, making direct observation from Earth impossible. Current in situ satellite measurements offer critical data but are limited in spatial and temporal coverage, leaving significant gaps in our understanding of radiation belt dynamics. Observations of the cyclo-synchrotron emission from the Moon’s near side could offer a unique position for real-time monitoring of radiation belts activity.
Given the typical energies of radiation belts electrons (10 keV - 1 MeV), the emitted signal follows the cyclo-synchrotron formalism. ONERA has developed a cyclo-synchrotron radiation simulator that uses the electron distributions from the physics-based Salammbô model [Marc et al., 2024].
Here, we present the development of inversion methods to retrieve the 3D distribution of electrons (Kinetic energy, Equatorial pitch angle, Roeder’s parameter L*) from simulated images of the cyclo-synchrotron radiation. A PCA-based approach demonstrates highly promising results, confirming the technical feasibility of this method and its potential to enhance our understanding of radiation belt dynamics.
With future lunar missions expected to deploy instruments capable of capturing 2D images of these emissions, developing robust inversion techniques will be essential to maximize the scientific return of these observations and enhance our space weather capabilities.
How to cite: Marc, G., Brunet, A., Sicard, A., and Nénon, Q.: Inversion Methods for Earth's Radiation Belt Observations from the Moon Using Cyclo-synchrotron emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8687, https://doi.org/10.5194/egusphere-egu25-8687, 2025.
Using nine years of plasma density and hiss wave observations from the Van Allen Probes, we have compiled a substantial dataset of time intervals featuring significant plasma density perturbations and hiss wave power. We extracted the upper and lower bounds of the plasma density variation as well as the hiss amplitude variation. Statistical analysis shows that the density difference (ΔlogN) has a strong positive correlation with both the hiss amplitude (logA) and the hiss amplitude difference (ΔlogA), indicating the modulation effect of plasma density on the hiss wave amplitude.
Using machine learning techniques, we developed a regression model to predict the hiss amplitude (logA and ΔlogA) from plasma density information, spatial position, and geomagnetic indexes. The modeling results show that incorporating the density difference ΔlogN into the model improves prediction accuracy. Feature importance analysis indicates that ΔlogN is the most important feature for predicting the hiss amplitude difference ΔlogA.
How to cite: Xia, Z., Chen, L., and Gu, W.: Investigate the Effect of Plasma Density Perturbation on the Hiss Wave Amplitude, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13416, https://doi.org/10.5194/egusphere-egu25-13416, 2025.
Electromagnetic ion cyclotron (EMIC) waves in the Earth’s inner magnetosphere are driven by ring current ions and play an essential role in electron and ion dynamics. Since their frequency ranges (0.1 ~ 10 Hz) are close to the cyclotron frequencies of protons (H+), singly ionized helium and oxygen ions (He+, O+), they can efficiently heat the cold ions via cyclotron resonance. In this study, we run a hybrid simulation in a homogeneous plasma including hot H+ (~100 keV) cold H+, He+, and O+, to investigate the EMIC wave properties after saturation and the associated heating of cold ions. We find that the spectrum of EMIC waves evolves towards smaller frequency as the waves saturate, resulting from the relaxation of the temperature anisotropy of hot H+. Accompanying with the frequency evolution, the efficient scattering on the ions shifts to heavier ions; that is, the cold H+, He+, and O+ are heated sequentially. The H+ and He+ are mainly heated perpendicularly with respect to the background magnetic field line, while the O+ are mainly heated near the field-aligned direction. Our study can advance the understanding of EMIC wave properties and their coupling with cold ions in the magnetosphere.
How to cite: Gu, S., Chen, L., Fu, X., Cowee, M., and Liu, X.: The saturation properties of EMIC waves and the associated heating of cold ions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13042, https://doi.org/10.5194/egusphere-egu25-13042, 2025.
Radial diffusion in planetary radiation belts is a dominant transport mechanism resulting in the energization and losses of charged
particles by large-scale electromagnetic fluctuations. In this work we exploit the extensive radial diffusion coefficients (DLL) database created
in the framework of the Horizon 2020 SafeSpace project, which spans 9 years of hourly DLL coefficients, to investigate the spatiotemporal
distributions of the coefficients. Our results indicate that the radial distribution of the magnetic and electric component of the
DLL, as well as their sum, the total DLL, can be well described by a power law function of L* in the [4.3–7.7] range. We show that the L*-
dependent spectral index varies significantly and is far from constant as assumed and implemented in many semi-empirical models. We
examine the quasi-periodic behavior of the radial profiles of the DLL throughout most of the 24th Solar cycle, which the data cover, and
find an approximately 420 days dominant periodicity. This periodic behavior is linked (in terms of cross-wavelet analysis) with solar
activity, nevertheless, its origin remains unclear. The uncovered features are important for understanding DLL behavior and drivers
as well as for current and future modelling efforts.
How to cite: Katsavrias, C., Aminalragia Giamini, S., Nasi, A., Papadimitriou, C., and Daglis, I. A.: Parameterization of the spatial and temporal distribution ofradial diffusion coefficients in the outer Van Allen belt, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3428, https://doi.org/10.5194/egusphere-egu25-3428, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 3
EGU25-4720 | ECS | Posters virtual | VPS27
Influence of solar wind driving and geomagnetic activity on the variability of sub-relativistic electrons in the inner magnetosphereThu, 01 May, 14:00–15:45 (CEST) | vP3.18
Motivated by the need for more accurate radiation environment modelling, this study focuses on identifying and analyzing the drivers behind the sub-relativistic electron flux variations in the inner magnetosphere. We utilize electron flux data between 1 and 500 keV from the Hope and MagEIS instruments on board the RBSP satellites, as well as from the FEEPS instruments on board the MMS spacecrafts, along with solar wind parameters and geomagnetic indices obtained from the OmniWeb2 and SuperMag data services. We calculate the correlation coefficients between these parameters and electron flux. Our analysis shows that substorm activity is a crucial driver of the source electron population (10 - 100 keV), while also showing that seed electrons (100 - 400 keV) are not purely driven by substorm events, but also from enhanced convection/inward diffusion. By introducing time lags, we observed a delayed response of electron flux to changes in geospace conditions, and we identified specific time lag periods where the correlation is maximum. This work contributes to our broader understanding of the outer belt sub-relativistic electron dynamics, and forms the basis for future research.
How to cite: Christodoulou, E., Katsavrias, C., Kordakis, P., and Daglis, I.: Influence of solar wind driving and geomagnetic activity on the variability of sub-relativistic electrons in the inner magnetosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4720, https://doi.org/10.5194/egusphere-egu25-4720, 2025.
