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Abstract While whistler‐mode waves are generated by injected anisotropic electrons on the nightside, the observed day‐night asymmetry of wave distributions raises an intriguing question about their generation on the dayside. In this study, we evaluate the distributions of whistler‐mode wave amplitudes and electrons as a function of distance from the magnetopause (MP) on the dayside from 6 to 18 hr in magnetic local time (MLT) within ±18° of magnetic latitude using the Time History of Events and Macroscale Interaction During Substorms measurements from June 2010 to August 2018. Specifically, under different levels of solar wind dynamic pressure and geomagnetic index, we conduct a statistical analysis to examine whistler‐mode wave amplitude, as well as anisotropy and phase space density (PSD) of source electrons across 1–20 keV energies, which potentially provide a source of free energy for wave generation. In coordinates relative to the MP, we find that lower‐band (0.05–0.5f_ce) waves occur much closer to the MP than upper‐band (0.5–0.8f_ce) waves, wheref_ceis electron cyclotron frequency. Our statistical results reveal that strong waves are associated with high anisotropy and high PSD of source electrons near the equator, indicating a preferred region for local wave generation on the dayside. Over 10–14 hr in MLT, as latitude increases, electron anisotropy decreases, while whistler‐mode wave amplitudes increase, suggesting that wave propagation from the equator to higher latitudes, along with amplification along the propagation path, is necessary to explain the observed waves on the dayside. 

Abstract We evaluate the diffusive and nonlinear scattering of ring current protons by electromagnetic ion cyclotron (EMIC) waves in the Earth's inner magnetosphere using test particle simulations. EMIC waves are commonly observed inside and outside the plasmasphere with wave amplitudes ranging from 100 pT to several nT. Field‐aligned EMIC waves can scatter 1 keV–1 MeV protons counter‐streaming with respect to the waves through first order cyclotron resonance. Through the analyses of the proton equatorial pitch angle variations along the field line, our simulations reveal the typical interaction features including quasilinear diffusion for small wave amplitudes, phase trapping and bunching at intermediate and large pitch angles, anomalous phase trapping and positive phase bunching at small pitch angles, and non‐resonant scattering at pitch angles and energies outside the resonance regime. Using different wave amplitudes from 100 pT to 5 nT, we compared the modeling results of proton equatorial pitch angle variations between quasilinear and test particle simulations, and between diffusive scattering and advective effects. For monochromatic He‐band EMIC waves atL = 5, the interaction between protons and EMIC waves with amplitudes below 500 pT could be described as a diffusive process and quantified by quasilinear theory; nonlinear interactions and advection effects become important for wave amplitudes larger than 1 nT. The interactions between EMIC waves and ring current protons are analogous to the interactions between whistler‐mode chorus waves and radiation belt electrons described in previous studies, despite the quantitative differences in the wave amplitude threshold of quasilinear diffusion applicability. 

Interchange instability is known to drive fast radial transport of particles in Jupiter's inner magnetosphere. Magnetic flux tubes associated with the interchange instability often coincide with changes in particle distributions and plasma waves, but further investigations are required to understand their detailed characteristics. We analyze representative interchange events observed by Juno, which exhibit intriguing features of particle distributions and plasma waves, including Z‐mode and whistler‐mode waves. These events occurred at an equatorial radial distance of ∼9 Jovian radii on the nightside, with Z‐mode waves observed at mid‐latitude and whistler‐mode waves near the equator. We calculate the linear growth rate of whistler‐mode and Z‐mode waves based on the observed plasma parameters and electron distributions and find that both waves can be locally generated within the interchanged flux tube. Our findings are important for understanding particle transport and generation of plasma waves in the magnetospheres of Jupiter and other planetary systems. 

Abstract We present statistical distributions of whistler‐mode chorus and hiss waves at frequencies ranging from the local proton gyrofrequency to the equatorial electron gyrofrequency (f_ce,eq) in Jupiter's magnetosphere based on Juno measurements. The chorus wave power spectral densities usually follow thef_ce,eqvariation with major wave power concentrated in the 0.05f_ce,eq–f_ce,eqfrequency range. The hiss wave frequencies are less dependent onf_ce,eqvariation than chorus with major power concentrated below 0.05f_ce,eq, showing a separation from chorus atM < 10. Our survey indicates that chorus waves are mainly observed at 5.5 < M < 13 from the magnetic equator to 20° latitude, consistent with local wave generation near the equator and damping effects. The hiss wave powers extend to 50° latitude, suggesting longer wave propagation paths without attenuation. Our survey also includes the whistler‐mode waves at high latitudes which may originate from the Io footprint, auroral hiss, or propagating hiss waves reflected to highMshells. 

Abstract Interchange instability is known to drive fast radial transport of electrons and ions in Jupiter's inner and middle magnetosphere. In this study, we conduct a statistical survey to evaluate the properties of energetic particles and plasma waves during interchange events using Juno data from 2016 to 2023. We present representative examples of interchange events followed by a statistical analysis of the spatial distribution, duration and spatial extent. Our survey indicates that interchange instability is predominant atM‐shells from 6 to 26, peaking near 17 with an average duration of minutes and a correspondingM‐shell width of <∼0.05. During interchange events, the associated plasma waves, such as whistler‐mode, Z‐mode, and electron cyclotron harmonic waves exhibit a distinct preferential location. These findings provide valuable insights into particle transport and the source region of plasma waves in the Jovian magnetosphere, as well as in other magnetized planets within and beyond our solar system. 

Abstract Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler‐mode waves and relativistic electrons using Juno measurements and wave‐particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV atMshell ∼11 near the magnetic equator during perijove‐31. The electron injections are related to chorus wave bursts at 0.05–0.5f_cefrequencies, wheref_ceis the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90° pitch angle, and the fluxes are high during injections. We calculate the whistler‐mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler‐mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1–10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave‐particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler‐mode waves in Jupiter's outer radiation belt. 

Abstract In this study, using Van Allen Probes observations we identify 81 events of electron flux bursts with butterfly pitch angle distributions for tens of keV electrons with close correlations with chorus wave bursts in the Earth's magnetosphere. We use the high‐rate electron flux data from Magnetic Electron Ion Spectrometer available during 2013–2019 and the simultaneous whistler‐mode wave measurements from Electric and Magnetic Field Instrument Suite and Integrated Science to identify the correlated events. The events are categorized into 67 upper‐band chorus (0.5–0.8f_ce) dominated events and 14 other events where lower‐band chorus (0.05–0.5f_ce) has modest or strong amplitudes (f_cerepresents electron cyclotron frequency). Each electron flux burst correlated with chorus has a short timescale of ∼1 min or less, suggesting potential nonlinear effects. The statistical distribution of selected electron burst events tends to occur in the post‐midnight sector atL > 5 under disturbed geomagnetic conditions, and is associated with chorus waves with relatively strong magnetic wave amplitude and small wave normal angle. The frequency dependence of the electron flux peaks agrees with the cyclotron resonant condition, indicating the effects of chorus‐induced electron acceleration. Our study provides new insights into understanding the rapid nonlinear interactions between chorus and energetic electrons. 

Abstract Electromagnetic ion cyclotron (EMIC) waves can drive radiation belt depletion and Low‐Earth Orbit satellites can detect the resulting electron and proton precipitation. The ELFIN (Electron Losses and Fields InvestigatioN) CubeSats provide an excellent opportunity to study the properties of EMIC‐driven electron precipitation with much higher energy and pitch‐angle resolution than previously allowed. We collect EMIC‐driven electron precipitation events from ELFIN observations and use POES (Polar Orbiting Environmental Satellites) to search for 10s–100s keV proton precipitation nearby as a proxy of EMIC wave activity. Electron precipitation mainly occurs on localized radial scales (∼0.3 L), over 15–24 MLT and 5–8 L shells, stronger at ∼MeV energies and weaker down to ∼100–200 keV. Additionally, the observed loss cone pitch‐angle distribution agrees with quasilinear predictions at ≳250 keV (more filled loss cone with increasing energy), while additional mechanisms are needed to explain the observed low‐energy precipitation.