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Abstract The geosynchronous orbit (GEO) is a region filled with energetic electrons and it hosts hundreds of satellites. Electron fluxes at GEO can change sharply within hours, making high‐time‐resolution prediction crucial. In this study, we develop and compare two neural networks for persistent high‐time‐resolution prediction: long short‐term memory with temporal pattern attention (TPA‐LSTM) and Transformer. Unlike most previous models, which only output electron fluxes, our models output the same parameters as the inputs, including magnetic local time, solar wind speed, solar wind dynamic pressure, AE, Kp, Dst, the north‐south component of the interplanetary magnetic field, and electron flux data from GOES‐15. The models are trained on approximately six years of data (2012–2016) and validated using about one year of data (2017–2018). We compare the TPA‐LSTM and Transformer models using >0.8 MeV electron fluxes and find that while the Transformer model performs slightly better, the difference is not statistically significant. Considering the Transformer's higher computational cost, we use the TPA‐LSTM model to develop prediction models for electron fluxes of 275, 475, >0.8 MeV, and >2 MeV with a 5‐min resolution at GEO, up to 3 days. The prediction efficiencies (PE) for 275, 475, >0.8 and >2 MeV electron fluxes based on about one year of test data (2018–2019) are 0.799, 0.831, 0.849, 0.881 (1‐day prediction); and 0.551, 0.618, 0.663 and 0.710 (3‐day prediction), respectively. Our high‐time‐resolution persistent models should be useful for both protecting satellites at GEO and serving as boundary conditions for physics‐based radiation belt models.

Magnetosonic waves are an important medium for energy transfer in collisionless space plasma. Magnetosonic waves have been widely investigated in the upstream of the bow shock at Mars. These waves are believed to originate from pickup ions or reflected particles. By utilizing MAVEN spacecraft data, we have observed the occurrence of quasi-perpendicularly propagating magnetosonic emissions near the proton gyrofrequency in the Martian magnetotail region. These plasma waves are associated with a significant enhancement of proton and oxygen flux. The excited magnetosonic waves could possibly heat the protons through resonance and facilitate the ionospheric plasma escape. Our results could be helpful to better understand the Mars’ magnetospheric dynamics and offer insights into possible energy redistribution between waves and plasma in the Martian nightside magnetosphere.

Abstract Chorus waves are naturally occurring electromagnetic emissions in space and are known to produce highly energetic electrons in the hazardous radiation belt. The characteristic feature of chorus is its fast frequency chirping, whose mechanism remains a long-standing problem. While many theories agree on its nonlinear nature, they differ on whether or how the background magnetic field inhomogeneity plays a key role. Here, using observations of chorus at Mars and Earth, we report direct evidence showing that the chorus chirping rate is consistently related to the background magnetic field inhomogeneity, despite orders of magnitude difference in a key parameter quantifying the inhomogeneity at the two planets. Our results show an extreme test of a recently proposed chorus generation model and confirm the connection between the chirping rate and magnetic field inhomogeneity, opening the door to controlled plasma wave excitation in the laboratory and space.

Whistler mode chorus waves are common and intense electromagnetic waves in the Earth's magnetosphere. They play a crucial role in magnetospheric electron dynamics by accelerating and scattering electrons over a wide energy range. Chorus waves are typically quasi-coherent emissions with frequency chirping. The generation mechanism of frequency chirping of whistler mode chorus has been debated for many years. Some theoretical and numerical models to explain the generation condition of chorus frequency chirping and the detailed nonlinear wave-particle interaction have been proposed. There are two main types of chorus wave generation models in history. The frequency chirping rate of the first model is proportional to the background magnetic field inhomogeneity. The prediction of this model is in good agreement with observation in the Earth's magnetosphere, but it cannot explain the frequency chirping with a uniform background magnetic field. Another model proposes that the frequency chirping rate is proportional to the wave amplitude and can be verified by self-consistent particle-in-cell simulations. However, the forms of the frequency chirping rate from the two theoretical models are very different. This paper will briefly review the observation of rising tone chorus waves, the optimal excitation condition of chorus, nonlinear wave particle interactions, and also the newly proposed "TaRA" (Trap-Release-Amplify) model. In this model, the wave source region near the equator is divided into upstream and downstream based on the wave propagation direction. These two regions play different roles in the wave excitation process. Phase space structures of correlated electrons are formed by nonlinear wave particle interactions, which mainly occur in the downstream of the equator. When released from the wave packet in the upstream, these electrons lead to selective amplification of new emissions which satisfy the phase-locking condition to maximize wave power transfer, resulting in frequency chirping. The similarities and differences between TaRA model and other mainstream models will be discussed. The study of the frequency chirping mechanism of chorus waves can not only explain the characteristics related to chorus fine structures, deepen the understanding of the nonlinear process of wave-particle interactions, but can also be used to explain other related phenomena, such as the frequency chirping of whistler waves in a uniform magnetic field, rising tone electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere, and the frequency chirping structures of chorus and EMIC waves at other planets.

Time-domain structures (TDS), manifested as ≥ 1 ms pulses with significant parallel electric fields, play an important role in accelerating electrons in the field-aligned direction. These precipitated electrons contribute to the formation of aurora. In this study, we present observations of time-domain structures that occurred in the plasmaspheric plumes at the post-midnight to dawn sector. The close correlation between TDS and plasmaspheric plumes implies that the generation of TDS might be modulated by plasma density. During the wave occurrence, protons with an energy level below 1 keV show the enhanced field-aligned pitch-angle distributions, and the electron fluxes with the energies ranging from tens to hundreds of eV are also significantly enhanced. The correlation between TDS and scattered particles indicates the importance of including time-domain structures in future studies of radiation belt dynamics.

We report observations of the whistler mode waves in the magnetic reconnection region at the dayside magnetopause using the magnetospheric multiscale (MMS) mission on January 11, 2016. In this event, whistlers mostly occur on the magnetospheric side of the reconnection central plane and are closely related to counter-streaming electron beams in the medium energy range (200--300 eV). These counter-streaming electron beams can be attributed to the accelerated magnetosheath electrons by the reconnection. Through quantitatively testing the Landau resonance condition and solving the kinetic dispersion relations, we present the evidence for whistler excitation by electron beams in the medium energy range. Additionally, the whistlers are observed simultaneously with the pitch-angle scattering of electrons in the high-energy range (300--3,000 eV). The calculation results show that this scattering is likely to occur through electron cyclotron wave-particle interactions, which can isotropize electrons and exchange energy between plasmas and waves. [ABSTRACT FROM AUTHOR]