A Theoretical Framework of Chorus Wave Excitation

Zonca, F.; Tao, X.; Chen, L.

doi:10.1029/2021ja029760

Cited by 24 publications

(36 citation statements)

References 62 publications

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“…The recent work of Zonca et al. (2021) presents a general theoretical framework for chorus excitation which hints at a fundamental connection between gyrotron backwave oscillators and other interpretations of chorus chirping (Omura & Nunn, 2011; Vomvoridis et al., 1982), supporting thus further experimental and theoretical research in this area.…”

Section: Summary and Discussionmentioning

confidence: 79%

Measurability of the Nonlinear Response of Electron Distribution Function to Chorus Emissions in the Earth's Radiation Belt

et al. 2021

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We conduct test particle simulations to study the perturbations in a hot electron velocity distribution caused by a rising chorus element propagating parallel to the ambient magnetic field in the Earth's outer radiation belt. The wavefield is constructed from the nonlinear growth theory of chorus emissions of Omura (2021, https://doi.org/10.1186/s40623-021-01380%2Dw), with additional considerations about saturation and propagation of the transverse resonant current being applied to model the subpacket structure. Using Liouville's theorem, we trace electrons back in time to reconstruct the evolution of electron velocity distribution at the magnetic equator. The electromagnetic hole created by nonlinear trapping and transport effects appears as a depression in the velocity distribution, aligned with the resonance velocity curve. We analyze the decrease of particle flux in this depression and estimate the energy resolution, pitch angle resolution, time resolution and geometric factor of particle analyzers needed to observe the perturbation. We conclude that particle detectors on current or recently operating spacecraft are always lacking in at least one of these parameters, which explains the missing direct observations of sharp phase space density depressions during chorus‐electron nonlinear resonant interaction. However, with a dedicated experiment and appropriate measurement strategy, such observations are within the possibilities of the current technology. Similarity of the simulated density perturbation and a step function mathematical model is used to draw an analogy between the backward wave oscillator regime of chorus generation and the nonlinear growth theory.

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Section: Summary and Discussionmentioning

confidence: 79%

Measurability of the Nonlinear Response of Electron Distribution Function to Chorus Emissions in the Earth's Radiation Belt

et al. 2021

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“…For the linear growth rate to be positive, we have A /( A + 1) − ω / Ω > 0 (Kennel & Petschek, 1966). Correspondingly, Δ f < 0 from Equation , which means that the phase space density carried by the trapped particles is larger than the neighboring phase space density, forming a phase space clump near the equator (Zonca et al., 2022). The formation and evolution of phase space clump will be clearly demonstrated by our PIC simulation in this paper.…”

Section: A Brief Review Of Nonlinear Wave‐particle Interaction Theorymentioning

confidence: 99%

“…Recently, based on the theoretical framework of Zonca et al. (2022), Zonca et al. (2021), Tao et al.…”

Section: Introductionmentioning

confidence: 99%

“…Assuming the chirping process and related phase space structures exist, Vomvoridis et al (1982) found that the chirping rate should be proportional to the amplitude of wave, which has been used by the Backward-Wave-Oscillator (BWO) model (Trakhtengerts, 1995) and verified by PIC simulations (Hikishima et al, 2009b;Katoh & Omura, 2013). Recently, based on the theoretical framework of Zonca et al (2022), Zonca et al (2021), Tao et al (2021) proposed the TaRA model, and successfully reproduced chirping rates of both Helliwell (1967) and Vomvoridis et al (1982). The model suggests that both background magnetic field inhomogeneity and wave amplitude should be related to the chirping rate, but at different stages of generation.…”

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confidence: 98%

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Nonlinear Electron Phase‐Space Dynamics in Spontaneous Excitation of Falling‐Tone Chorus

Tao

Zonca

et al. 2022

Geophysical Research Letters

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Whistler mode chorus, characterized by frequency chirping, is an important type of waves in planetary magnetospheres. To investigate the role of nonlinear wave particle interactions in excitation of chorus, analysis of electron phase space dynamics is required. While electron phase hole associated with rising tone chorus has been well studied, the phase space structure corresponding to falling tone chorus is less understood. Here, we investigate in detail the electron phase space dynamics in a spontaneously generated falling tone chorus with a parabolic type magnetic field, where field strength decreases away from the equator. We demonstrate the formation and evolution of electron phase space clump from downstream to upstream regions, and show that the variation of frequency chirping rate is caused by the movement of the source region. The results are consistent with the recently proposed Trap‐Release‐Amplify model, and should be useful to understand the mechanism of chorus frequency chirping.

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“…The phasetrapped particles are forced to stay in resonance with the wave over large spatial scales, and this effect is generally believed to be responsible for the generation of chorus. Even so, the detailed dynamics of phase-trapped particles during the wave generation process is still actively researched despite several decades of analysis (Trakhtengerts, 1999;Tao et al, 2017;Omura, 2021;Zonca et al, 2022). A key outstanding question is at what stage in the trapping process are the amplifying currents formed.…”

Section: Introductionmentioning

confidence: 99%

Backward-propagating source as a component of rising tone whistler-mode chorus generation

Harid

Gołkowski

Hosseini

et al. 2022

Front. Astron. Space Sci.

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Whistler-mode chorus waves in the magnetosphere play a crucial role in space weather via wave–particle interactions. The past two decades have observed tremendous advances in theory and simulations of chorus generation; however, several details of the generation mechanism are still actively contended. To simulate chorus generation, a new envelope particle-in-cell code is introduced. The model produces a rising tone chorus element in a parabolic geomagnetic field. The initial chorus element “embryo” frequency is shown to initialize near the equator at the frequency of maximum linear growth. A backward resonant current is then observed to propagate upstream of the equator. The trajectory of the backward current follows that of a freely falling electron that has been de-trapped at the equator superimposed with forward motion at the group velocity. The backward current iteratively radiates a rising tone element where the highest frequency components are generated furthest upstream. The work provides new advancements in modeling chorus and corroborates other recent work that has also demonstrated a backward-moving source during the generation of coherent whistler-mode waves.

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A Theoretical Framework of Chorus Wave Excitation

Cited by 24 publications

References 62 publications

Measurability of the Nonlinear Response of Electron Distribution Function to Chorus Emissions in the Earth's Radiation Belt

Measurability of the Nonlinear Response of Electron Distribution Function to Chorus Emissions in the Earth's Radiation Belt

Nonlinear Electron Phase‐Space Dynamics in Spontaneous Excitation of Falling‐Tone Chorus

Backward-propagating source as a component of rising tone whistler-mode chorus generation

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