Magnetosonic Harmonic Falling and Rising Frequency Emissions Potentially Generated by Nonlinear Wave‐Wave Interactions in the Van Allen Radiation Belts

et al. 2020

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Electromagnetic ion cyclotron (EMIC) waves play an important role in the energy transfer among particles of different energies and species in the magnetosphere, whose drivers have been commonly recognized as solar wind compressions and storm/substorm proton injections. However, how the solar wind decompressions related to frequently occurring discontinuities compete with the proton injections in the evolution of EMIC waves has been rarely investigated. Here we present a complete end‐to‐end observation by Wind, THEMIS, and Van Allen Probes missions during the main phase of the 23 February 2014 storm of a succession of solar wind rotational discontinuities decompressing the magnetosphere within 200 s, adiabatically decelerating the freshly injected >10 keV protons, and thus suppressing the EMIC waves in the inner magnetosphere. Our results highlight the importance of solar wind conditions for the evolution of inner magnetospheric EMIC waves from a new perspective.

K_{normali} = γ false/ false| bold v_{g} false|,

γ = \frac{1}{\frac{\partial D}{\partial ω}} \frac{4 π e^{2}}{ε_{0} m_{normalH}} \frac{P false(R - L false)}{ω^{2}} N_{normalR} \cdot ()(, A_{normalR} - A_{normalC}),

N_{normalR} = 2 π \frac{{normalΩ}_{normalH} - ω}{k} \cdot \int_{0}^{\infty} v_{⊥} d v_{⊥} F {true|}_{v_{false‖} = v_{normalR}},

A_{normalR} = \int_{0}^{\infty} v_{⊥} d v_{⊥} ()(, v_{false‖} \frac{\partial F}{\partial v_{⊥}} - v_{⊥} \frac{\partial F}{\partial v_{false‖}}) \frac{v_{⊥}}{v_{<...>}}

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Section: Physical Mechanismsmentioning

confidence: 99%

Can Solar Wind Decompressive Discontinuities Suppress Magnetospheric Electromagnetic Ion Cyclotron Waves Associated With Fresh Proton Injections?

Liu

et al. 2020

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“…Perraut et al (1982) found that nonlinear sum-frequency interactions can occur between magnetosonic branches in the first harmonic and produce higher harmonic structures, which is analogous to the situation of the second event. Recently, Liu et al (2018) reported nonlinear difference-frequency interactions between locally generated magnetosonic waves and a propagating magnetosonic wave. Our results, together with previous studies, provide a comprehensive picture of the nonlinear interactions of Bernstein-mode waves.…”

Section: Discussionmentioning

confidence: 99%

Evidence of Nonlinear Interactions Between Magnetospheric Electron Cyclotron Harmonic Waves

Zuo

Feng

et al. 2020

Electron cyclotron harmonic (ECH) waves play an important role in the magnetosphere‐ionosphere coupling. They are usually considered to be generated by the Bernstein‐mode instability with electron loss cone distributions. By analyzing the Van Allen Probes wave data, we present the direct evidence of the nonlinear interactions between ECH waves in the magnetosphere. Substorm‐injected electrons excite primary ECH waves in a series of structureless bands between multiples of the electron gyrofrequency. Nonlinear interactions between the primary ECH waves produce secondary waves at sum‐ and difference‐frequencies of the primary waves. Our results suggest that the nonlinear wave‐wave interactions can redistribute the primary ECH wave energy over a broader frequency range and hence potentially affect the magnetospheric electrons over a broader range of pitch angles and energies.

“…Recently, there has been a resurgence of interest in the nonlinear wave‐wave interactions within the magnetosphere. Three‐wave resonances are invoked to explain the multibanded or highly oblique whistler waves (Agapitov et al, ; Fu et al, ; Gao et al, ; Teng et al, ; Vasko et al, ) and the magnetosonic harmonic falling/rising frequency waves (Liu et al, ). Here we present the first evidence for the nonlinear coupling between chorus and ECH waves and highlight the energy redistribution among the resonant waves.…”

Section: Discussionmentioning

confidence: 99%

Nonlinear Coupling Between Whistler‐Mode Chorus and Electron Cyclotron Harmonic Waves in the Magnetosphere

Xiao

et al. 2018

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Electromagnetic whistler‐mode chorus and electrostatic electron cyclotron harmonic (ECH) waves can contribute significantly to auroral electron precipitation and radiation belt electron acceleration. In the past, linear and nonlinear wave‐particle interactions have been proposed to explain the occurrences of these magnetospheric waves. By analyzing Van Allen Probes data, we present here the first evidence for nonlinear coupling between chorus and ECH waves. The sum‐frequency and difference‐frequency interactions produced the ECH sidebands with discrete frequency sweeping structures exactly corresponding to the chorus rising tones. The newly generated weak sidebands did not satisfy the original electrostatic wave dispersion relation. After the generation of chorus and normal ECH waves by hot electron instabilities, the nonlinear wave‐wave interactions could additionally redistribute energy among the resonant waves, potentially affecting to some extent the magnetospheric electron dynamics.