Gap formation around 0.5Ωe of whistler-mode waves excited by electron temperature anisotropy

2021 ◽  
Author(s):  
Huayue Chen ◽  
Xinliang Gao ◽  
Quanming Lu ◽  
Konrad Sauer
Keyword(s):  
Electron Temperature ◽  
Electron Distribution ◽  
Wave Spectrum ◽  
Linear Stage ◽  
Gap Formation ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Pic Simulation ◽  
Distribution Form ◽  
Whistler Mode Waves

<p>With a 1-D PIC simulation model, we have investigated the gap formation around 0.5Ω<sub>e</sub> of the quasi-parallel whistler-mode waves excited by an electron temperature anisotropy. When the frequencies of excited waves in the linear stage cross 0.5Ω<sub>e</sub>, or when they are slightly larger than 0.5Ω<sub>e </sub>but then drift to lower values, the Landau resonance can make the electron distribution form a beam-like/plateau population. Such an electron distribution only slightly changes the dispersion relation of whistler-mode waves, but can cause severe damping around 0.5Ω<sub>e</sub> via cyclotron resonance. At last, the wave spectrum is separated into two bands with a power gap around 0.5Ω<sub>e</sub>. The condition under different electron temperature anisotropy and plasma beta is also surveyed for such kind of power gap. Besides, when only the waves with frequencies lower than 0.5Ω<sub>e</sub> are excited in the linear stage, a power gap can also be formed due to the wave-wave interactions, i.e., lower band cascade. Our study provides a clue to reveal the well-known 0.5Ω<sub>e</sub> power gap of whistler-mode waves ubiquitously observed in the inner magnetosphere.</p>

Gap Formation Around 0.5Ω e of Whistler‐Mode Waves Excited by Electron Temperature Anisotropy

2021 ◽  
Vol 126 (2) ◽  
Author(s):  
Huayue Chen ◽  
Xinliang Gao ◽  
Quanming Lu ◽  
Konrad Sauer ◽  
Rui Chen ◽  
...  
Keyword(s):  
Electron Temperature ◽  
Gap Formation ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Whistler Mode Waves

scholarly journals Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations

2009 ◽  
Vol 27 (6) ◽  
pp. 2259-2275 ◽  
Author(s):  
O. Le Contel ◽  
A. Roux ◽  
C. Jacquey ◽  
P. Robert ◽  
M. Berthomier ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Temperature ◽  
Linear Theory ◽  
Broad Band ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Background Magnetic Field ◽  
Whistler Mode Waves ◽  
Liouville’S Theorem

Abstract. We report on quasi-parallel whistler emissions detected by the near-earth satellites of the THEMIS mission before, during, and after local dipolarization. These emissions are associated with an electron temperature anisotropy α=T⊥e/T||e>1 consistent with the linear theory of whistler mode anisotropy instability. When the whistler mode emissions are observed the measured electron anisotropy varies inversely with β||e (the ratio of the electron parallel pressure to the magnetic pressure) as predicted by Gary and Wang (1996). Narrow band whistler emissions correspond to the small α existing before dipolarization whereas the broad band emissions correspond to large α observed during and after dipolarization. The energy in the whistler mode is leaving the current sheet and is propagating along the background magnetic field, towards the Earth. A simple time-independent description based on the Liouville's theorem indicates that the electron temperature anisotropy decreases with the distance along the magnetic field from the equator. Once this variation of α is taken into account, the linear theory predicts an equatorial origin for the whistler mode. The linear theory is also consistent with the observed bandwidth of wave emissions. Yet, the anisotropy required to be fully consistent with the observations is somewhat larger than the measured one. Although the discrepancy remains within the instrumental error bars, this could be due to time-dependent effects which have been neglected. The possible role of the whistler waves in the substorm process is discussed.

scholarly journals The generation of Ganymede's diffuse aurora through pitch angle scattering

2017 ◽  
Vol 35 (2) ◽  
pp. 239-252
Author(s):  
Arvind K. Tripathi ◽  
Rajendra P. Singhal ◽  
Onkar N. Singh II
Keyword(s):  
Electron Temperature ◽  
Pitch Angle ◽  
Atomic Oxygen ◽  
Particle Interaction ◽  
Distribution Functions ◽  
Dissociative Excitation ◽  
Kappa Distribution ◽  
Loss Cone ◽  
Whistler Mode ◽  
Whistler Mode Waves

Abstract. Diffuse auroral intensities of neutral atomic oxygen OI λ1356 Å emission on Ganymede due to whistler mode waves are estimated. Pitch angle diffusion of magnetospheric electrons into the loss cone due to resonant wave–particle interaction of whistler mode waves is considered, and the resulting electron precipitation flux is calculated. The analytical yield spectrum approach is used for determining the energy deposition of electrons precipitating into the atmosphere of Ganymede. It is found that the intensities (4–30 R) calculated from the precipitation of magnetospheric electrons observed near Ganymede are inadequate to account for the observational intensities (≤ 100 R). This is in agreement with the conclusions reached in previous works. Some acceleration mechanism is required to energize the magnetospheric electrons. In the present work we consider the heating and acceleration of magnetospheric electrons by electrostatic waves. Two particle distribution functions (Maxwellian and kappa distribution) are used to simulate heating and acceleration of electrons. Precipitation of a Maxwellian distribution of electrons can produce about 70 R intensities of OI λ1356 Å emission for electron temperature of 150 eV. A kappa distribution can also yield a diffuse auroral intensity of similar magnitude for a characteristic energy of about 100 eV. The maximum contribution to the estimated intensity results from the dissociative excitation of O2. Contributions from the direct excitation of atomic oxygen and cascading in atomic oxygen are estimated to be only about 1 and 2 % of the total calculated intensity, respectively. The findings of this work are relevant for the present JUNO and future JUICE missions to Jupiter. These missions will provide new data on electron densities, electron temperature and whistler mode wave amplitudes in the magnetosphere of Jupiter near Ganymede.

scholarly journals Study of Oblique Propagating Whistler Mode Waves in Presence of Parallel DC Electric Field in Magnetosphere of Saturn

2017 ◽  
Vol 6 (2) ◽  
pp. 26 ◽  
Author(s):  
R. Kaur ◽  
R. S. Pandey
Keyword(s):  
Growth Rate ◽  
Distribution Function ◽  
Energy Density ◽  
Wave Number ◽  
Number Density ◽  
Temperature Anisotropy ◽  
Loss Cone ◽  
Whistler Mode ◽  
Whistler Mode Waves ◽  
Magnetosphere Of Saturn

In this paper whistler mode waves have been investigated in magnetosphere of Saturn. The derivation for perturbed distribution function, dispersion relation and growth rate have been determined by using the method of characteristic and kinetic approach. Analytical expressions for growth rate and real frequency of whistlers propagating oblique to magnetic field direction are attained. Calculations have been performed at 6 radial distances in plasma sheet region of Saturn’s magnetosphere as per data provided by Cassini. Work has been extended for bi-Maxwellian as well as Loss-cone distribution function. Parametric analysis show that temperature anisotropy, increase in number density, energy density and angle of propagation increases the growth rate of whistler waves along with significant shift in wave number. In case of Loss-cone distribution, increase in growth rate of whistlers is significantly more than for bi-Maxwellian distribution function. Generation of second harmonics can also be seen in the graphs plotted. It is concluded that parallel DC field stabilizes the wave and temperature anisotropy, angle of propagation, number density and energy density of electrons enhances the growth rate. Thus the results are of importance in analyzing observed VLF emissions over wide spectrum of frequency range in Saturnian magnetosphere. The analytical model developed can also be used to study various types of instabilities in planetary magnetospheres. 

scholarly journals Long-term evolution of electron distribution function due to nonlinear resonant interaction with whistler mode waves

2018 ◽  
Vol 84 (2) ◽  
Author(s):  
Anton V. Artemyev ◽  
Anatoly I. Neishtadt ◽  
Alexei A. Vasiliev ◽  
Didier Mourenas
Keyword(s):  
Kinetic Equation ◽  
Electron Distribution ◽  
Resonant Interaction ◽  
Long Term Evolution ◽  
Radiation Belts ◽  
Linear Diffusion ◽  
Whistler Mode ◽  
Term Evolution ◽  
Whistler Mode Waves

Accurately modelling and forecasting of the dynamics of the Earth’s radiation belts with the available computer resources represents an important challenge that still requires significant advances in the theoretical plasma physics field of wave–particle resonant interaction. Energetic electron acceleration or scattering into the Earth’s atmosphere are essentially controlled by their resonances with electromagnetic whistler mode waves. The quasi-linear diffusion equation describes well this resonant interaction for low intensity waves. During the last decade, however, spacecraft observations in the radiation belts have revealed a large number of whistler mode waves with sufficiently high intensity to interact with electrons in the nonlinear regime. A kinetic equation including such nonlinear wave–particle interactions and describing the long-term evolution of the electron distribution is the focus of the present paper. Using the Hamiltonian theory of resonant phenomena, we describe individual electron resonance with an intense coherent whistler mode wave. The derived characteristics of such a resonance are incorporated into a generalized kinetic equation which includes non-local transport in energy space. This transport is produced by resonant electron trapping and nonlinear acceleration. We describe the methods allowing the construction of nonlinear resonant terms in the kinetic equation and discuss possible applications of this equation.

scholarly journals Study of whistler mode instability in Saturn's magnetosphere

2006 ◽  
Vol 24 (6) ◽  
pp. 1705-1712 ◽  
Author(s):  
R. P. Singhal ◽  
A. K. Tripathi
Keyword(s):  
Diffusion Coefficients ◽  
Pitch Angle ◽  
Temperature Anisotropy ◽  
Mode Instability ◽  
Whistler Mode ◽  
Energy Diffusion ◽  
Whistler Mode Waves ◽  
Magnetosphere Of Saturn ◽  
Temporal Growth Rate ◽  
Good Agreement

Abstract. A dispersion relation for parallel propagating whistler mode waves has been applied to the magnetosphere of Saturn and comparisons have been made with the observations made by Voyager and Cassini. The effect of hot (suprathermal) electron-density, temperature, temperature anisotropy, and the spectral index parameter, κ, on the temporal growth rate of the whistler mode emission is studied. A good agreement is found with observations. Electron pitch angle and energy diffusion coefficients have been obtained using the calculated temporal growth rates.

scholarly journals Electron-scale sheets of whistlers close to the magnetopause

2005 ◽  
Vol 23 (12) ◽  
pp. 3715-3725 ◽  
Author(s):  
G. Stenberg ◽  
T. Oscarsson ◽  
M. André ◽  
A. Vaivads ◽  
M. Morooka ◽  
...  
Keyword(s):  
High Energy ◽  
Diffusion Region ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Plasma Drift ◽  
High Energy Electrons ◽  
Whistler Mode Waves ◽  
Thin Electron ◽  
Field Lines ◽  
The Waves

Abstract. Whistler emissions close to the magnetopause on the magnetospheric side are investigated using the four Cluster spacecraft. The waves are found to be generated in thin (electron-scale) sheets moving with the plasma drift velocity. A feature in the electron data coincides with the waves; hot magnetospheric electrons disappear for a few satellite spins. This produces or enhances a temperature anisotropy, which is found to be responsible for the generation of the whistler mode waves. The high energy electrons are thought to be lost through the magnetopause and we suggest that the field lines, on which the waves are generated, are directly connected to a reconnection diffusion region at the magnetopause.

Unified theory of whistler mode instability in the presence of a parallel electric field

1984 ◽  
Vol 31 (2) ◽  
pp. 263-274
Author(s):  
Indra Mohan Lal Das ◽  
R. P. Singh
Keyword(s):  
Electric Field ◽  
Full Range ◽  
Present Theory ◽  
Parallel Electric Field ◽  
Temperature Anisotropy ◽  
Whistler Mode ◽  
Plasma Injection ◽  
Whistler Mode Waves ◽  
Particle Pressure ◽  
Analytical Expressions

The propagation characteristics of right-hand circularly polarized whistler mode waves propagating parallel to the external magnetic field in an anisotropic plasma have been reformulated including the effect of a parallel electric field. Analytical expressions for the real frequency and growth rate have been obtained for the full range of the parameters β (the ratio of particle pressure to magnetic pressure of the hot particles), A (temperature anisotropy) and P ( = βA(A + 1)2) without any restriction on the magnitude of the imaginary part of the wave frequency. The effect of cold plasma injection on the marginal instability has also been studied. Possible application of the present theory to the atmospheres of Earth and Jupiter has been discussed.

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