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Ion-scale magnetic holes are nonlinear plasma structures commonly observed in the solar wind and Earth's magnetosphere. These holes are characterized by the magnetic field depletion filled by hot, transversely anisotropic ions and electrons and are likely formed during the nonlinear stage of ion mirror instability. Due to the plasma thermal anisotropy within magnetic holes, they serve as a host of electromagnetic ion cyclotron waves, whistler-mode waves, and electron cyclotron harmonic waves. This makes magnetic holes an important element of the Earth's inner magnetosphere, where electromagnetic waves generated within may strongly contribute to energetic ion and electron scattering. Such scattering, however, will modify the hot-ion distribution that is trapped within magnetic holes and responsible for the magnetic field stress balance. Therefore, hot ion scattering within magnetic holes likely determines the hole lifetime. In this study, we investigate how ion scattering by electromagnetic waves affects the stress balance and lifetime of magnetic holes. For illustration, we used typical characteristics of magnetic holes, ion populations, and ion cyclotron waves observed in the Earth's magnetosphere. We have demonstrated that ion distribution isotropization via scattering by waves does not change significantly magnetic hole magnitude, but ion losses due to scattering into the atmosphere may limit the hole life-times to 10–30 min in the Earth's inner magnetosphere. 

Abstract Electromagnetic ion cyclotron (EMIC) waves effectively scatter relativistic electrons in Earth's radiation belts and energetic ions in the ring current. Empirical models parameterizing the EMIC wave characteristics are important elements of inner magnetosphere simulations. Two main EMIC wave populations included in such simulations are the population generated by plasma sheet injections and another population generated by magnetospheric compression due to the solar wind. In this study, we investigate a third class of EMIC waves, generated by hot plasma sheet ions modulated by compressional ultra‐low frequency (ULF) waves. Such ULF‐modulated EMIC waves are mostly observed on the dayside, between magnetopause and the outer radiation belt edge. We show that ULF‐modulated EMIC waves are weakly oblique (with a wave normal angle ) and narrow‐banded (with a spectral width of of the mean frequency). We construct an empirical model of the EMIC wave characteristics as a function of ‐shell and MLT. The low ratio of electron plasma frequency to electron gyrofrequency around the EMIC wave generation region does not allow these waves to scatter energetic electrons. However, these waves provide very effective (comparable to strong diffusion) quasi‐periodic precipitation of plasma sheet protons. 

Abstract The two most important wave modes responsible for energetic electron scattering to the Earth's ionosphere are electromagnetic ion cyclotron (EMIC) waves and whistler‐mode waves. These wave modes operate in different energy ranges: whistler‐mode waves are mostly effective in scattering sub‐relativistic electrons, whereas EMIC waves predominately scatter relativistic electrons. In this study, we report the direct observations of energetic electron (from 50 keV to 2.5 MeV) scattering driven by the combined effect of whistler‐mode and EMIC waves using ELFIN measurements. We analyze five events showing EMIC‐driven relativistic electron precipitation accompanied by bursts of whistler‐driven precipitation over a wide energy range. These events reveal an enhancement of relativistic electron precipitation by EMIC waves during intervals of whistler‐mode precipitation compared to intervals of EMIC‐only precipitation. We discuss a possible mechanism responsible for such precipitation. We suggest that below the minimum resonance energy (E_min) of EMIC waves, the whistler‐mode wave may both scatter electrons into the loss‐cone and accelerate them to higher energy (1–3 MeV). Electrons accelerated aboveE_minresonate with EMIC waves that, in turn, quickly scatter those electrons into the loss‐cone. This enhances relativistic electron precipitation beyond what EMIC waves alone could achieve. We present theoretical support for this mechanism, along with observational evidence from the ELFIN mission. We discuss methodologies for further observational investigations of this combined whistler‐mode and EMIC precipitation. 

Abstract Energetic electron losses in the Earth's inner magnetosphere are dominated by outward radial diffusion and scattering into the atmosphere by various electromagnetic waves. The two most important wave modes responsible for electron scattering are electromagnetic ion cyclotron (EMIC) waves and whistler‐mode waves (whistler waves) that, acting together, can provide rapid electron losses over a wide energy range from few keV to few MeV. Wave‐particle resonant interaction resulting in electron scattering is well described by quasi‐linear diffusion theory using the cold plasma dispersion, whereas the effects of nonlinear resonances and hot plasma dispersion are less well understood. This study aims to examine these effects and estimate their significance for a particular event during which both wave modes are quasi‐periodically modulated by ultra‐low‐frequency (ULF) compressional waves. Such modulation of EMIC and whistler wave amplitudes provides a unique opportunity to compare nonlinear resonant scattering (important for the most intense waves) with quasi‐linear diffusion (dominant for low‐intensity waves). The same modulation of plasma properties allows better characterization of hot plasma effects on the EMIC wave dispersion. Although hot plasma effects significantly increase the minimum resonant energy,E_min, for the most intense EMIC waves, such effects become negligible for the higher frequency part of the hydrogen‐band EMIC wave spectrum. Nonlinear phase trapping of 300–500 keV electrons through resonances with whistler waves may accelerate and make them resonant with EMIC waves that, in turn, quickly scatter those electrons into the loss‐cone. Our results highlight the importance of nonlinear effects for simulations of energetic electron fluxes in the inner magnetosphere. 

Abstract Observations from past space missions report on the significant abundance of N⁺, in addition to those of O⁺, outflowing from the terrestrial ionosphere and populating the near‐Earth region. However, instruments on board current space missions lack the mass resolution to distinguish between the two, and often the role of N⁺in regulating the magnetosphere dynamics, is lumped together with that of O⁺ions. For instance, our understanding regarding the role of electromagnetic ion cyclotron (EMIC) waves in controlling the loss and acceleration of radiation belt electrons and ring current ions has been based on the contribution of He⁺and O⁺ions only. We report the first observations by Van Allen Probes of linearly polarized N⁺EMIC waves, which confirm the presence of N⁺in the terrestrial magnetosphere, and open up new avenues to particle energization, loss, and transport mechanisms, based on the altered magnetospheric plasma composition.