Dependence of Generation of Whistler Mode Chorus Emissions on the Temperature Anisotropy and Density of Energetic Electrons in the Earth's Inner Magnetosphere

Katoh, Yutai; Omura, Yoshiharu; Miyake, Yohei; Nakashima, Hiroshi

doi:10.1002/2017ja024801

Cited by 24 publications

(36 citation statements)

References 45 publications

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“…The hot/source electron density

n_{h}

affects

B_{o p}

and amplitude growth rate. We set a proper ratio of hot electron density to cold electron density

n_{h} false/ n_{e} = 0.005

, which is a reasonable value based on observations and simulations (e.g., Juhász et al, ; Katoh et al, ; Kurita et al, ; Santolík et al, ). The parameters used for the wave generation are listed in Table .…”

Section: Simulation Methodsmentioning

confidence: 99%

Nonlinear Evolution of Radiation Belt Electron Fluxes Interacting With Oblique Whistler Mode Chorus Emissions

2020

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Nonlinear whistler mode wave‐particle interaction is one of the processes to generate relativistic electrons in the Earth's outer radiation belt. Applying test particle simulations with a pair of whistler mode chorus emissions, we traced a large number of electrons in various initial conditions along an L=4.5 magnetic field line to build a set of Green's functions for analyzing evolution of the electron distribution under the chorus emissions. Employing convolution integral for the Green's functions, we tracked the formation of relativistic electron fluxes from an injected energetic electron through interaction with consecutive chorus emissions. We compared the simulation results among a purely parallel wave model and two oblique wave models with wave normal angles gradually increased from 0° to 20° and 60°. Multiple resonances result in a higher probability of nonlinear trapping. Hence, the trapped electrons for the oblique cases are scattered to a wider range of pitch angles than those for the parallel case. Oblique chorus can accelerate 10–30 keV electrons to MeV level rapidly in several wave emission cycles (about 10 s), which is much faster than that of the parallel wave model. The study shows comprehensive evolutions of electron fluxes interacting with oblique chorus emissions through cyclotron and Landau resonances in the outer radiation belt.

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“…The hot/source electron density

n_{h}

affects

B_{o p}

and amplitude growth rate. We set a proper ratio of hot electron density to cold electron density

n_{h} false/ n_{e} = 0.005

Section: Simulation Methodsmentioning

confidence: 99%

Nonlinear Evolution of Radiation Belt Electron Fluxes Interacting With Oblique Whistler Mode Chorus Emissions

2020

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“…Both of these currently limit the usability of these codes for studying radiation belts electron dynamics during long time periods (e.g., >2 days). Test‐particle codes are used to investigate the self‐consistent nonlinear mechanism of wave generation and growth in the radiation belts (e.g., Omura et al, 2009; Hikishima et al, ; Omura & Zhao, , ; Chen et al, ; Katoh et al, ; Omura et al, ). Nevertheless, wave particle interaction in this context is at the forefront of the field, with, for instance, Omura et al () using test particle simulation for studying energetic electrons acceleration in resonant interaction with a chorus wave packet.…”

Section: New Radiation Belt Modeling Capabilities and The Quantificatmentioning

confidence: 99%

Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions

et al. 2020

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The past decade transformed our observational understanding of energetic particle processes in near‐Earth space. An unprecedented suite of observational systems was in operation including the Van Allen Probes, Arase, Magnetospheric Multiscale, Time History of Events and Macroscale Interactions during Substorms, Cluster, GPS, GOES, and Los Alamos National Laboratory‐GEO magnetospheric missions. They were supported by conjugate low‐altitude measurements on spacecraft, balloons, and ground‐based arrays. Together, these significantly improved our ability to determine and quantify the mechanisms that control the buildup and subsequent variability of energetic particle intensities in the inner magnetosphere. The high‐quality data from National Aeronautics and Space Administration's Van Allen Probes are the most comprehensive in situ measurements ever taken in the near‐Earth space radiation environment. These observations, coupled with recent advances in radiation belt theory and modeling, including dramatic increases in computational power, have ushered in a new era, perhaps a “golden era,” in radiation belt research. We have edited a Journal of Geophysical Research: Space Science Special Collection dedicated to Particle Dynamics in the Earth's Radiation Belts in which we gather the most recent scientific findings and understanding of this important region of geospace. This collection includes the results presented at the American Geophysical Union Chapman International Conference in Cascais, Portugal (March 2018) and many other recent and relevant contributions. The present article introduces and review the context, current research, and main questions that motivate modern radiation belt research divided into the following topics: (1) particle acceleration and transport, (2) particle loss, (3) the role of nonlinear processes, (4) new radiation belt modeling capabilities and the quantification of model uncertainties, and (5) laboratory plasma experiments.

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“…Since the values of R 2 for T LA , T NLA , D F , and D NF are all above 70%, the confidence levels are all good in the performance of the RF method. Here we note that Katoh et al () simulated the chorus development in terms of the number density of energetic electrons normalized by a fixed number density of cold electrons. They found that the threshold amplitude is smaller when the number density of energetic electrons is larger.…”

Section: An Evaluation Of Importance In Feature Variables By Random Fmentioning

confidence: 99%

A Systematic Study in Characteristics of Lower Band Rising‐Tone Chorus Elements

et al. 2019

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Chorus waves are usually generated outside the plasmapause in the equatorial region of the magnetosphere. The discrete characteristics of chorus elements are quantified by the three parameters: lasting time, frequency bandwidth, and repetition period. A systematic study in the lasting time and frequency bandwidth in terms of background plasma and magnetic fields has not been performed in the past. Here we use burst mode waveform data from the Time History of Events and Macroscale Interaction during Substorms (THEMIS) probes and the random forest method of machine learning and Pearson's correlation analysis to investigate which background plasma and magnetic field parameter is dominant over the lasting time and frequency bandwidth. We find that the temperature is the most important parameter that controls the lasting time. The lasting time is shorter when this temperature is higher. We also find that the normalized bandwidth by the local electron cyclotron frequency is controlled by the number density of energetic electrons. The normalized bandwidth is wider when this number density is larger. These results can be well explained by the threshold and optimum wave amplitudes for the nonlinear generation of chorus waves (Omura & Nunn, 2011, https://doi.org/10.1029/2010JA016280). The findings derived from this analysis can be used to serve as a guideline for a deep understanding of the generation mechanism of chorus elements and help choose input for a modeling of wave‐particle interactions in the radiation belts.

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Dependence of Generation of Whistler Mode Chorus Emissions on the Temperature Anisotropy and Density of Energetic Electrons in the Earth's Inner Magnetosphere

Cited by 24 publications

References 45 publications

Nonlinear Evolution of Radiation Belt Electron Fluxes Interacting With Oblique Whistler Mode Chorus Emissions

Nonlinear Evolution of Radiation Belt Electron Fluxes Interacting With Oblique Whistler Mode Chorus Emissions

Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions

A Systematic Study in Characteristics of Lower Band Rising‐Tone Chorus Elements

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