During the largest geomagnetic storm of Solar Cycle 25 that happened in May 2024, the Arase satellite has successfully operated all instruments and observed a number of remarkable phenomena in the inner magnetosphere and radiation belts. Due to significant compression of the magnetosphere caused by an interplanetary shock, the satellite's apogee was located outside the magnetosphere, indicating a substantial degree of compression. Following the main phase of the storm, a rapid flux increase of high-energy electrons with energies of several MeV was observed in the region of L < 3. This was the largest flux increase event recorded ever since the launch of the Arase satellite.
Additionally, the plasmasphere contracted inward more than usual, with the plasmapause reaching L ~ 2. The enhanced flux of high-energy electrons at L < 3 persisted for an extended period of 10 to 30 days or even more, significantly changing the radiation environment near the Earth. Analyzing observation data from the Arase satellite, we estimated the decay time constant of the electrons and compared it with the rates of pitch-angle scattering caused by various plasma waves, such as hiss waves, VLF transmitters, and lightning whistlers. The results suggest that continuous scattering driven by plasmaspheric hiss primarily governs the decay of those high-energy electrons. In this presentation, we report on the variations in the radiation belts and inner magnetosphere observed by the Arase satellite during this historic geomagnetic storm.
How to cite: Miyoshi, Y., Shinohara, I., Takashima, T., Asamura, K., Mitani, T., Higashio, N., Kasahara, S., Yokota, S., Kataoka, R., Kumar, S., Hori, T., Kurita, S., Matsuda, S., Katoh, Y., Kasahara, Y., Tsuchiya, F., Kumamoto, A., Shinbori, A., Matsuoka, A., and Kitamura, N. and the ERG Project Team: Arase Observations of the Radiation Belts During the May 2024 Geomagnetic Storm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5458, https://doi.org/10.5194/egusphere-egu25-5458, 2025.
The physical mechanisms usually applied to explain the relativistic electron enhancement have been delved into to elucidate non-adiabatic electron acceleration resulting in the ultra-relativistic electron population observed in the outer radiation belt. We considered multisatellite observations of the solar wind parameters, magnetospheric waves, and particle flux to report an unusual local acceleration of ultra-relativistic electrons under a prolonged high-speed solar wind stream (HSS). A corotating interaction region reaches the Earth’s bowshock on August 3, 2016, causing a minor geomagnetic storm. Following this, the magnetosphere was driven for 72 hours by a long-term HSS propagating at 600 km/s. During this period, the magnetosphere sustained both ultra-low frequency (ULF) and very-low frequency (VLF) waves in the outer radiation belt region. Besides the waves, the relativistic and ultra-relativistic electron fluxes were enhanced with different time lags regarding the magnetic storm main phase. The efficiency of wave-particle interaction in enhancing ultrarelativistic electrons is evaluated by the diffusion coefficient rates, considering both ULF and VLF waves together with phase space density analyses. Results show that local acceleration by whistler mode chorus waves can occur in a time scale of 2 to 4 hours, whereas ULF waves take around 10’s of hours and magnetosonic waves take a time scale of days. This result is confirmed by the phase space density analysis. Accordingly, it shows that peaks of local acceleration of 1 MeV electrons are consistent with the observation of the highest chorus wave amplitude at the same L-shell and MLT. Thus, we argue that whistler mode chorus waves interacting with relativistic electrons are the main physical mechanisms leading to ultra-relativistic electron enhancement, while ULF and fast magnetosonic waves are found as secondary physical processes. Lastly, our analysis contributes to understanding how whistler and ULF waves can contribute to ultra-relativistic electrons showing up in the inner magnetosphere under the HSS driver.
How to cite: Alves, L., da Silva, L., Deggeroni, V., Marchezi, J. P., Jauer, P. R., and G. Sibeck, D.: Ultra-Relativistic Electron Flux Enhancement Under Persistent High-Speed Solar Wind Stream, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20519, https://doi.org/10.5194/egusphere-egu25-20519, 2025.
Measurements from the Van Allen Probes mission show sporadic and diffi cult-to- predict behavior at ultra-relativistic energies. Recent observational studies demonstrated that cold plasma has a controlling effect over the ultra-relativistic electrons that are million times more energetic. However, the global modeling of the dynamics of relativistic and ultra-relativistic electrons has been missing. In this study, we present the modeling of 3D radiation belts with a variable density, demonstrating that density has a controlling effect over acceleration to these high energies. The density is obtained by using the VERB-CS code with data assimilation. In this study, we also present an analysis of observations showing what are the unique conditions in the solar wind and in the magnetosphere required for the density depletions and for the acceleration of particles to ultra-relativistic energies.
How to cite: Shprits, Y., Haas, B., and Wang, D.: Acceleration to ultra-relativistic energies by a VERB-3D code coupled to a data- assimilative plasmasphere code VERB-CS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8357, https://doi.org/10.5194/egusphere-egu25-8357, 2025.
To obtain a comprehensive global morphology of the ECH waves, we combine the high-quality observations from the recent satellites of Van Allen Probes, Arase, and Magnetospheric Multiscale from 2012 to 2022. With the well-accumulated data, we find that ECH waves can be observed over a broad spatial region with significant asymmetry. Primarily, ECH waves can be observed from L= ~2.5 and extend to L = ~15 on the nightside while dayside waves are compressed closer to the Earth. On the nightside, the waves are observed more frequently at low L with strong wave strength. As L increases, both wave occurrence and amplitude decline. It is noteworthy that ECH waves exhibit a double peak pattern at L = ~4-6 and 8-12 on the dayside, and a dip of occurrence at L = 6-8, which might indicate two dominant driving mechanisms of ECH waves on the inner and outer magnetosphere, respectively. At low L, ECH waves are observed near the equator, while they can be observed extensively over the magnetic latitude of ~-40° — 40° at higher L. Compared with the nightside, the magnetic latitude sensitivity to the increase of L is more dramatic on the dayside. Furthermore, at low latitudes, ECH waves can be observed with broad MLT coverage and have strong wave amplitude at low L. For high latitudes, the waves occur at higher L, with higher occurrence on the dayside while stronger wave strength on the nightside. Our results provide a new insight into the generating and propagating mechanism of ECH waves.
How to cite: Lou, Y., Ni, B., Cao, X., and Ma, X.: Global Distribution of Electrostatic Electron Cyclotron Harmonic Waves from Over-10-year Multi-Satellite Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11036, https://doi.org/10.5194/egusphere-egu25-11036, 2025.
Magnetic reconnection hosts regions of enhanced ion temperature anisotropy that could drive instabilities and excite magnetosonic waves. However, the relation between magnetosonic-mode fluctuations and the anti-dipolarization fronts (ADFs, also known as the leading edge of tailward reconnection jets), is still unclear. Here, for the first time, we provide direct observations of magnetosonic-mode fluctuations behind ADF by the magnetospheric multiscale mission. These compressible waves propagate quasi perpendicularly to the background magnetic fields at very slow phase speeds (~30 km/s) and appears simultaneously with parallel ion temperature anisotropy. Such waves were likely a result of oblique firehose instability. An electron rolling-pin distribution is modulated by such waves behind the ADF: at wave troughs (B minimum), perpendicular electron fluxes are high; at wave crests (B maximum), perpendicular electron fluxes are low. Fermi acceleration and magnetic mirror effect contribute to the formation of such distribution jointly. These findings improve our understanding of wave-particle interactions near the ADFs in Earth's magnetosphere.
How to cite: Zhang, W. and Fu, H.: Magnetosonic-mode fluctuations and electron rolling-pin distribution behind anti-dipolarzation front in terrestrial magnetotail, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6461, https://doi.org/10.5194/egusphere-egu25-6461, 2025.
The stability of weakly collisional plasmas is well represented by linear theory, and the generated waves play an essential role in the thermodynamics of these systems. The velocity distribution functions (VDF) characterizing kinetic particle behavior are commonly represented as a sum of anisotropic bi-Maxwellians. A three bi-Maxwellian model is commonly applied for the ions, assuming that the VDF consists of a proton core, proton beam, and a single He (alpha) particle population, each with their own density, bulk velocity, and anisotropic temperature. Resolving an alpha beam component was generally not possible due to instrumental limitations. The Solar Orbiter Solar Wind Analyser Proton and Alpha Sensor (SWA PAS) resolves velocity space with sufficient coverage and accuracy to routinely characterize secondary alpha populations consistently. This design makes the SWA PAS ideal for examining effects of alpha-particle beam on the plasma's kinetic stability. We test the wave signatures observed in the magnetic field power spectrum at ion scales and compare them to the predictions from linear plasma theory, Doppler-shifted into the spacecraft reference frame. We find that taking into account the alpha-particle beam component is necessary to predict the coherent wave signatures in the observed power spectra, emphasizing the importance of separating the alpha-particle populations as is traditionally done for protons. Moreover, we demonstrate that the drifts of beam components are responsible for the majority of the modes that propagate in oblique direction to the magnetic field, while their temperature anisotropies are the primary source of parallel Fast Magnetosonic Modes in the solar wind.
How to cite: Martinović, M., Klein, K., De Marco, R., Verscharen, D., Bruno, R., and D'Amicis, R.: Impact of Two-Population Alpha-particle Distributions on Plasma Stability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7498, https://doi.org/10.5194/egusphere-egu25-7498, 2025.
Standard numerical solutions of multi-dimensional diffusion equations often yield negative, unphysical phase space densities. To address this, we present Sayram, an open-source 3D code for modeling electron flux evolution in Earth’s radiation belts. Using a recently proposed positivity-preserving finite volume method, Sayram ensures physically realistic solutions across a variety of 1D, 2D, and 3D test cases. Its implicit formulation removes constraints from the CFL condition, enabling efficient time stepping. Importantly, the computational overhead associated with ensuring positivity preservation is negligibly small, making Sayram as efficient as other non-positivity-preserving codes based on standard finite difference methods under the same simulation parameters. While developed for radiation belt studies and forecasting, Sayram can also be applied to study general multi-dimensional diffusion processes in other areas, such as wave-particle interactions in planetary magnetospheres and the solar wind. By combining positivity preservation, efficiency, and openness, Sayram provides a robust tool for research across multiple disciplines.
How to cite: Tao, X., Peng, P., Albert, J., and Chan, A.: Sayram: A Positivity-Preserving Open Source 3D Radiation Belt Modeling Code, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4672, https://doi.org/10.5194/egusphere-egu25-4672, 2025.
Magnetosonic (MS) waves are low frequency, compressional electromagnetic oscillations commonly observed in Earth’s inner magnetosphere and Martian upper ionosphere, propagating nearly perpendicular to the background magnetic field. These waves typically have frequencies between the local proton gyrofrequency and the local lower hybrid frequency, exhibiting linear polarization. MS waves are known to accelerate and pitch angle scatter relativistic killer electrons in Earth’s radiation belts [1]. In the Martian ionosphere, they contribute to heating heavier oxygen ions and facilitate their escape [2]. Concurrent wave and particle data from various satellite missions within Earth’s magnetosphere suggest that MS waves arise from the ring-like velocity distribution of energetic protons with a positive perpendicular slope [1].
A comprehensive theoretical model comprising of hot, tenuous Maxwellian ring-distributed energetic protons and the cold background of Maxwellian protons, heavier ions (O+ and O2+), and electrons is developed using kinetic theory to study the generation of magnetosonic waves in a homogenous collisionless plasma system. The derivation of the dispersion relation, and consequently the growth rate expression, requires solving both parallel and perpendicular velocity integrals. The perpendicular integrals associated with the Maxwellian ring distribution lack analytical solutions and are therefore computed numerically. In contrast, the parallel integrals are solved analytically using series expansion of the plasma dispersion function, with approximations applied depending on whether the particle species is cold or energetic. The model is validated using plasma parameters pertinent to Earth’s inner magnetosphere and the Martian upper ionosphere. Results reveal that the model generates sharp MS wave harmonics within the range of the local proton cyclotron frequency to the local lower hybrid frequency at highly oblique propagation angles.
The developed theoretical model is used to study the linear growth rate of MS wave instability in Earth’s inner magnetosphere and Martian upper ionosphere. A parametric comparison study is done on the energy of the ring proton population optimum for the wave generation. The influence of the ambient magnetic field and cold background plasma on the growth and damping of MS waves in terrestrial and Martian environments will be discussed.
References
[1] R. B. Horne et al., Geophys. Res. Lett. 34, L17107 (2007)
[2] J. Wang et al., Geophys. Res. Lett. 50, L102911 (2023)
How to cite: Amrutha, , Singh, S., Barik, K., and Lakhina, G.: A Comprehensive Theoretical Model for the Generation of Magnetosonic Waves in Terrestrial and Planetary Plasma Environments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-856, https://doi.org/10.5194/egusphere-egu25-856, 2025.
The acceleration of radiation belt electrons through resonant interactions with whistler-mode waves is typically analyzed using quasilinear theory, which treats phase space density spreading across energy and pitch angle as a diffusive process. However, nonlinear resonant interactions can result in distinctly non-diffusive transport, accelerating seed electron populations to several MeV within minutes under idealized scenarios. This rapid energization contrasts with spacecraft observations, which are generally well explained by Fokker-Planck models using quasilinear diffusion coefficients.
We investigate conditions under which nonlinear acceleration can be approximated as diffusion. Test-particle simulations with increasingly complex wave field models reveal two principal types of resonant electron motion. First, for single-frequency, high-amplitude waves, electrons move along resonant diffusion curves, or analogous curves in inhomogeneous magnetic fields, spreading uniformly along these curves within a few tens of seconds. Above ~500 keV, relativistic turning acceleration (RTA) and ultra-relativistic acceleration (URA) mechanisms can increase particle energies by several MeV within a few seconds.
Second, with realistic wave models including finite bandwidth and amplitude modulations, electrons can move across diffusion curves corresponding to different wave frequencies. This process, orders of magnitude slower than the idealized motion along diffusion curves, can be accurately described as diffusion. In addition, wave incoherence significantly disrupts phase trapping, slowing down nonlinear acceleration along the curves. On the time scale of several consecutive resonant interactions, electron dynamics become stochastic, and the acceleration along the curves can be effectively described as inhomogeneous diffusion with negligible advection.
We conclude that, under realistic conditions, electron acceleration happening over multiple bounce periods and longer timescales can be modeled by the Fokker-Planck equation with energy-dependent corrections to quasilinear diffusion coefficients. Efficient modeling approaches that avoid computationally expensive kinetic simulations are critical for advancing radiation belt numerical models.
How to cite: Hanzelka, M., Shprits, Y., Wang, D., and Haas, B.: Limiting processes in the non-linear and non-diffusive acceleration of radiation belt electrons by whistler-mode waves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9961, https://doi.org/10.5194/egusphere-egu25-9961, 2025.
Whistler-mode chorus waves, characterized by discrete, repetitive, narrowband emissions with frequency chirping, play a critical role in magnetospheric dynamics particularly in radiation belt electron interactions. These waves, predominantly observed in the dawn side of Earth's magnetosphere, exhibit significant variability in chirping rates, ranging from less than 1 kHz/s to over 10 kHz/s. Over the past few decades, extensive theoretical researches have been conducted to explain the frequency chirping of chorus waves, and two typical theoretical chirping rates have been proposed, one related to magnetic field inhomogeneity and the other linked to wave amplitude. To assess the performance of these theoretical chirping rates in practical application, we automatically identify 3166 lower band rising tone chorus wave elements from Van Allen Probes observations by using a geometric method (Radon Transform), and compare the theoretical predictions with observations. Our statistical analysis reveals that the theoretical chirping rates associated with magnetic field inhomogeneity align more closely with observations than those linked to wave amplitudes. Our findings not only validate the theoretical prediction in practical application but also highlight the importance of magnetic field gradients in shaping chorus wave dynamics.
How to cite: Wu, Z., Teng, S., Wu, Y., and Tao, X.: Uncertainties in Theoretical Chorus Chirping Rates: A Comparative Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5556, https://doi.org/10.5194/egusphere-egu25-5556, 2025.
Electromagnetic whistler-mode waves observed within the Earth’s radiation belts, in the Earth’s magnetotail, and at the bow shock may have sufficiently high amplitudes to resonate with electrons nonlinearly. In inhomogeneous background magnetic field such nonlinear resonant interactions should result in electron acceleration. In this presentation we compare efficiency of such acceleration for plasma parameters characteristic for the inner magnetosphere, magnetotail, and Earth’s bow shock. We show that despite a clear similarity in basic physics of electron acceleration for these three plasma systems, the efficiency of this acceleration is quite different. We also discuss observational evidence of nonlinear resonant interactions and possible approaches for modeling effects of such interactions in large-scale simulation setups.
How to cite: Artemyev, A., Vainchtein, D., and Zhang, X.: Efficiency of nonlinear resonant acceleration of electrons by high-frequency whistler-mode waves in the Earth’s radiation belt, Earth’s magnetotail, and at the bow shock., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2399, https://doi.org/10.5194/egusphere-egu25-2399, 2025.
Electron distributions associated with injections can be unstable to various high-frequency waves and low-frequency kinetic Alfven waves (KAW). Such scattering, often associated with resonances, causes a pitch-angle diffusion and generates diffuse auroral precipitation. In particular, standing mode KAWs can scatter pitch-angles of radiation belt electrons with energies above a few hundred keV through drift-bounce resonances, but the time scales of such scattering are too long for short-time injections. As a result, it was long thought that the main population of injected electrons, those with energies of tens to hundreds of keV, were unaffected by KAWs. In the present talk we show how KAWs can scatter electrons at two locations: near the reflection (bottleneck) points and in the current sheet. We also show how the presence of depolarization fronts change the scattering rates.
How to cite: Vainchtein, D., Danenova, S., and Artemyev, A.: Contributions of reflection poins and current sheet on scattering of energetic electrons by Kinetic Alfven Waves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5238, https://doi.org/10.5194/egusphere-egu25-5238, 2025.
Energetic electron precipitation from the outer radiation belt is a key mechanism of electron loss in Earth’s magnetosphere. This precipitation is largely governed by resonant interactions between electrons and electromagnetic ion cyclotron (EMIC) waves or whistler-mode waves. For sufficiently intense waves, these interactions become inherently nonlinear, characterized by rapid timescales and substantial precipitating fluxes that fall outside the framework of classical quasi-linear diffusion. In this presentation, we provide an overview of ELFIN CubeSat observations, showcasing compelling evidence of precipitation driven by nonlinear resonant interactions. We further discuss potential approaches for integrating the effects of these nonlinear interactions into radiation belt modeling frameworks.
How to cite: Zhang, X.-J., Angelopoulos, V., Mourenas, D., and Artemyev, A.: The Role of Nonlinear Resonant Interactions in Energetic Electron Precipitation: Insights from ELFIN Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5570, https://doi.org/10.5194/egusphere-egu25-5570, 2025.
Wave-particle interaction is one of the most crucial processes driving energy transport and conversion in the Earth's inner magnetosphere, leading to acceleration and diffusion of energetic electrons. Accurate characterization of these interaction mechanisms is essential for advancing our understanding of energetic electron dynamics within the ring current/radiation belts. In this study, we investigate the influence of wave-particle interactions on the phase space density and its variations in the ring current using a kinetic ring current model STRIM. The bounce-averaged Fokker-Planck equation in a dipole magnetic field is solved via a stochastic differential equation (SDE) equation, and diffusion coefficients are derived based on statistically analyzed wave properties from the Van Allen Probes (RBSP). By comparing diffusion coefficients, we find that energy diffusion and cross-diffusion terms play significant roles in the overall diffusion process. Comparative analysis on the effects of pitch angle diffusion and cross-diffusion on ring current electrons is also conducted to deepen our understanding of the diffusion process driven by wave-particle interaction.
How to cite: An, D., Yu, Y., Ma, L., Wei, Z., and Wu, H.: Simulating the Effect of Energy and Pitch angle Mixed diffusion on Ring Current Electron dynamics Based on the STRIM Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6614, https://doi.org/10.5194/egusphere-egu25-6614, 2025.
The Fokker-Planck diffusion equation is widely used for simulating the evolution of Earth's radiation belt electrons, which pose significant hazards to space-borne systems. To preserve the positivity of the numerical solution of the electron phase space density, several finely designed finite difference, Monte Carlo, spatiotemporal interpolation, and finite volume schemes have been developed. However, these schemes often suffer from either high implementation complexity or low execution efficiency. Here we propose an efficient, easy-to-implement, and positivity-preserving finite difference scheme, named the Semi-Implicit Logarithmic Linearization (SILL) scheme. The basic principle is to linearize the nonlinear equation of the natural logarithmic phase space density. This scheme ensures accuracy and stability, even with large time steps, up to hundreds of seconds for typical radiation belt electron diffusion processes. We have publicly released the protype code of the SILL scheme, which could be useful for the radiation belt modeling community.
How to cite: Qi, C., Su, Z., Wu, Z., Zheng, H., and Wang, Y.: An Efficient Positivity-Preserving Finite Difference Scheme for Solving the Fokker-Planck Diffusion Equation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7640, https://doi.org/10.5194/egusphere-egu25-7640, 2025.
The whistler-mode chorus is a distinctive electromagnetic emission featuring a frequency chirping. It arises from the nonlinear interaction between resonant electrons and traveling whistler packets inside the Earth's magnetosphere. In this research, we have proposed a novel Hamiltonian theory and developed a corresponding Vlasov simulation code to study the excitation of coherent chorus waves in weakly inhomogeneous magnetic fields. The onset of chorus wave is simulated with different initial conditions and narrow/wide banded excitation source. The formation and evolution of electron phase-space trapped holes are traced, and the accompanying frequency chirping of chorus waves is recovered. Notably, we found a new chorus wave generation process when the excitation source and initial wave spectrum are extremely narrow-banded. These excited waves follow a completely novel dispersion relationship, that differs significantly from that of the linear whistler waves. This study offers a fresh perspective on the nonlinear dynamics of chorus waves and provides important guidance for further research on the behavior of chorus waves across wide parameter ranges.
How to cite: Zheng, J., Wang, G., Li, B., and Zhou, T.: Vlasov Simulation of Coherent Chorus Wave Emission in the Earth’s Magnetosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10349, https://doi.org/10.5194/egusphere-egu25-10349, 2025.
During peaks of magnetospheric activity, energetic electrons trapped in the inner magnetosphere can precipitate in the lower ionosphere due to electromagnetic wave activity. Such waves can be generated naturally or artificially, for instance, through the emission of plasma beams. In this work, we study waves generated by electron beams emitted parallel to the magnetic field using fully kinetic Particle-In-Cell simulations. To this end, we use the heavily parallelized SMILEI code. To reduce the weight of the simulation, we take advantage of the rotational symmetry of the problem and use a cylindrical frame, which reduces the simulation to a 2D problem with cylindrical symmetry. We investigate the impact of the beam characteristics (such as beam density, frequency, length, etc.) on the wave generation, and the structural evolution of the beam as it exchanges energy with the electromagnetic fields and interacts with the background plasma.
How to cite: Dargent, J., Ripoll, J.-F., Beck, A., Le Contel, O., and Retinó, A.: Particle-In-Cell simulations of an electron beam: stability and wave emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10538, https://doi.org/10.5194/egusphere-egu25-10538, 2025.
Plasmaspheric hiss plays a crucial role in shaping the structure and dynamics of the radiation belts in the plasmasphere. Recent researches indicated that the characteristics and excitation mechanisms of low-frequency hiss differ markedly from those of typical frequency bands. Using the wave data observed by Van Allen Probes A from September 2012 to March 2019, we conducted a comprehensive statistical analysis of the global distribution of the average amplitude and occurrence rate of low-frequency hiss waves. We also explore the relationship between low-frequency hiss and geomagnetic activities as well as solar wind dynamic pressures (Pdyn). Our results reveal significant differences in the amplitude and occurrence rate distributions between low-frequency hiss and broad-band hiss, particularly regarding the distribution on the L-shell. The large amplitude low-frequency hiss waves are primarily observed at the afternoon side of the L > 5 region, shifting towards the noon side as geomagnetic activity intensifies. Furthermore, both the amplitude and occurrence rate of low-frequency hiss diminish with increasing solar wind dynamic pressure, and the occurrence rate of large amplitudes low-frequency hiss exhibits a North-South asymmetry under conditions of strong solar wind dynamic pressure. Our statistical results are vital for complementing the existing global distribution model of plasmaspheric hiss and for investigating its generation mechanism.
How to cite: Ma, X., Chen, S., Ni, B., Xiang, Z., Zhu, Q., and Lou, Y.: Influences of Geomagnetic Activities and Solar Wind Parameters on Global Distributions of Low-frequency Plasmaspheric Hiss based on Van Allen Probe A Measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11057, https://doi.org/10.5194/egusphere-egu25-11057, 2025.
Quasilinear diffusion coefficients can be used to characterise the statistical response of charged particles to perturbations by plasma waves, via resonant wave-particle interactions. The calculation of these coefficients is sufficiently complicated and arduous to render it prohibitive to many potential users, because of the expense in time spent developing the code. We present and describe the open-source PIRAN software package ('Particles In ResonANce'). This package is written using Python, has comprehensive documentation, and allows the user to calculate local and bounce-averaged relativistic diffusion coefficients in energy and pitch-angle space via the two main current proposed methods in the literature.
How to cite: Allanson, O., Kappas, T., Tyrrell, J., Cunningham, G., Garcia, A., and Elvidge, S.: Diffusion coefficients for resonant relativistic wave-particle interactions using the PIRAN code, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14871, https://doi.org/10.5194/egusphere-egu25-14871, 2025.
Earth’s radiation belts can be described by two zones containing energetic charged particles; a more stable inner belt, and a highly dynamic outer belt. Wave-particle interactions have been identified as one of several processes responsible for the dynamics of electron populations within the outer region. The most common method used by the international community for reproducing radiation belt dynamics involves Fokker-Planck diffusion models. Whilst, in many cases, these models effectively describe the global changes and interactions within the region, the Fokker-Planck approach depends upon a quasilinear theory. This assumes "small" wave amplitudes; however, recent observations have shown that this assumption may not always hold, with chorus waves being one of the most notable cases of high-amplitude waves.
Within two datasets of differing resolutions, the Van Allen Probe satellites provide multiple years' worth of information on the various waves and background fields inside the radiation belts. In this work, we present preliminary results of investigations comparing the lower resolution ‘survey mode’ data, with the high-resolution ‘burst mode’ data, captured during the mission. In particular, the work focusses on identifying chorus wave events in both datasets and assessing how the underlying variability may alter our interpretations of the wave properties. Utilizing the higher resolution data in conjunction with the survey data allows closer inspection of the larger amplitude waves, and their potential implications for energetic electron dynamics in radiation belt modelling.
How to cite: Black, R., Allanson, O., Meredith, N., Hillier, A., and Hartley, D.: Investigating chorus wave peak amplitudes on short timescales during the Van Allen Probes era , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17579, https://doi.org/10.5194/egusphere-egu25-17579, 2025.
Many numerical models for studying radiation belt dynamics have been built to uncovering the physical mechanisms governing electron dynamics and enabling real-time forecasting. A critical input for these models is the diffusion coefficient obtained through linear interpolation from precomputed diffusion coefficient libraries to achieve real-time processing. However, linear interpolation unavoidably introduces overlap issues, compromising both the accuracy and realism of the simulation results. In this study, we propose a diffusion Coefficient Interpolation Neural nEt (CINE) model, inspired by video frame interpolation, to address overlap issues. The CINE model does not require any preexisting diffusion coefficients for training and successfully interpolates diffusion coefficients induced by various physical mechanisms. We also analyze optimal interpolation intervals for different diffusion coefficients (ΔL≤0.8 for hiss waves and ΔL≤0.2 for atmospheric collisions) based on a threshold of Structural Similarity Index Measure (SSIM)=0.98. The CINE model is easy to incorporate with current radiation belts models to obtain accurate and prompt simulation results for real-time forecasting.
How to cite: wang, J., xiang, Z., ni, B., liu, Y., dong, J., guo, H., and dai, J.: Interpolating Electron Diffusion Coefficients in Earth’s Radiation Belts Based on A Neural Network Model Inspired by Video Frame Interpolation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18024, https://doi.org/10.5194/egusphere-egu25-18024, 2025.
The 19.8 kHz very‐low‐frequency (VLF) signals emitted from ground‐based North West Cape (NWC) transmitter for submarine communication can penetrate the ionosphere and leak into the magnetosphere. These signals interact with hundreds of keV electrons in the inner magnetosphere through cyclotron resonance, leading to the pitch angle diffusion of trapped electrons. Previous studies use the term “wisp” to describe the enhancement of quasi-trapped electron scattered by NWC transmitter signals at L = 1.4-1.8, which shows decreasing energy with increasing L. These quasi-trapped electrons drift eastward and can be clearly observed by Low-Earth-Orbit satellites until they precipitate into the South Atlantic Anomaly (SAA) region, where they are lost into the atmosphere. In this study, we report the ‘wisp’ structure in the untrapped electrons and systematically analyze the dependence of these electron fluxes on satellite positions, electron energies, L-shell, and geomagnetic activities using long-term measurements from the DEMETER satellite. The ‘wisp’ structure in untrapped electrons was observed at the edge of the northern hemisphere precipitation region (the regions conjugated to the SAA), with the flux level approximately 102-103 cm−2ster−1s−1MeV−1. The intensity and position of the untrapped ‘wisp’ in the energy spectrum are highly correlated with the quasi-trapped ‘wisp’. The visible ‘wisp’ structure in the untrapped electrons can only be detected when the quasi-trapped electrons, scattered by the NWC signal, exceed a certain threshold (i.e., greater than 103 cm−2ster−1s−1MeV−1). The overall variation in untrapped electron fluxes follows the trend observed in trapped electron fluxes. These results provide helpful information regarding the quantitative scattering effects of NWC transmitter signals on energetic electrons.
How to cite: hu, J., xiang, Z., ni, B., liu, Y., dong, J., wang, J., and guo, H.: Study of the precipitation wisp scattered by NWC transmitter signals: observed by DEMETER satellite., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18267, https://doi.org/10.5194/egusphere-egu25-18267, 2025.
