Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant wave‐particle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L < 8. However, we find from Time History of Events and Macroscale (THEMIS) Interactions during Substorms observations of fast flows at L = 12 that oblique whistler chorus emissions play the dominant role in scattering electrons. Previous works have identified whistler‐mode waves within fast flows that are produced by an electron temperature anisotropy T e ,⊥ / T e ,|| > 1, consistent with electron betatron acceleration. Here, however, we find whistler chorus emissions throughout an interval of fast flows where T e ,⊥ / T e ,|| < 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigar‐shaped distributions are consistent with Fermi acceleration at dipolarizations in fast flows. We demonstrate that the scattering efficiency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast flows. The obliquity of the whistler waves permits efficient scattering of lower‐energy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important free‐energy source for the wave‐particle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions.

In the present paper, we have calculated electron pitch angle diffusion coefficients due to resonant interactions with whistler mode lower band chorus (LBC), upper band chorus (UBC), and electrostatic electron cyclotron harmonic (ECH) waves. Calculations have been performed at two values of the ratio of electron plasma frequency to gyro-frequency and thirteen representative values of electron energies for the plasma sheet electrons. The numerical data of diffusion coefficients have been fitted to simple analytical expressions for each wave mode. These analytical expressions allow for simple evaluation of pitch angle diffusion coefficients for the arbitrary pitch angle, energy, the ambient magnetic field, the wave amplitude, and the ratio of plasma frequency to gyro-frequency. In the case of LBC waves, the analytical coefficients are generally within a factor of two to the numerical coefficients, except at higher pitch angles where the numerical coefficients drop to show negligible values. Likewise, also for UBC waves, the analytical coefficients are generally within a factor of two to the numerical coefficients. The analytical coefficients for ECH waves are generally in agreement with numerical coefficients. However, the analytical expressions developed for ECH waves do not reproduce sharp fluctuations, dips, and gaps, the so-called banded structure observed in the data of numerical coefficients [A. K. Tripathi et al., Phys. Plasmas 23, 042101 (2016)] The effect of the shape variation on the profile of the wave spectral intensity and the effect of cold temperature on the numerical coefficients are also investigated. Applications of the analytical expressions of diffusion coefficients are discussed.

The role of electrostatic electron cyclotron harmonic (ECH) waves in producing diffuse auroral emission O I 1356 angstrom on Ganymede is investigated. Electron precipitation flux entering the atmosphere of Ganymede due to pitch-angle diffusion by ECH waves into the atmospheric loss-cone is calculated. The analytical yield spectrum approach for electron energy degradation in gases is used for calculating diffuse auroral intensities. It is found that calculated O I 1356 angstrom intensity resulting from the precipitation of magnetospheric electrons observed near Ganymede is insufficient to account for the observed diffuse auroral intensity. This is in agreement with estimates made in earlier works. Heating and acceleration of ambient electrons by ECH wave turbulence near the magnetic equator on the field line connecting Ganymede and Jupiter are considered. Two electron distribution functions are used to simulate the heating effect by ECH waves. Use of a Maxwellian distribution with temperature 100 eV can produce about 50-70 Rayleigh O I 1356 angstrom intensities, and the kappa distribution with characteristic energy 50 eV also gives rise to intensities with similar magnitude. Numerical experiments are performed to study the effect of ECH wave spectral intensity profile, ECH wave amplitude, and temperature/characteristic energy of electron distribution functions on the calculated diffuse auroral intensities. The proposed missions, joint NASA/ESA Jupiter Icy Moon Explorer and the present JUNO mission to Jupiter, would provide new data to constrain the ECH wave and other physical parameters near Ganymede. These should help confirm the findings of the present study.

Both electron cyclotron harmonic (ECH) waves and whistler mode chorus waves resonate with electrons of the Earth's plasma sheet in the energy range from tens of eV to several keV and produce the electron diffuse aurora at ionospheric altitudes. Interaction of these superthermal electrons with the neutral atmosphere leads to the production of secondary electrons (E<500-600eV) and, as a result, leads to the activation of lower energy superthermal electron spectra that can escape back to the magnetosphere and contribute to the thermal electron energy deposition processes in the magnetospheric plasma. The ECH and whistler mode chorus waves, however, can also interact with the secondary electrons that are coming from both of the magnetically conjugated ionospheres after they have been produced by initially precipitated high-energy electrons that came from the plasma sheet. After their degradation and subsequent reflection in magnetically conjugate atmospheric regions, both the secondary electrons and the precipitating electrons with high (E>600eV) initial energies will travel back through the loss cone, become trapped in the magnetosphere, and redistribute the energy content of the magnetosphere-ionosphere system. Thus, scattering of the secondary electrons by ECH and whistler mode chorus waves leads to an increase of the fraction of superthermal electron energy deposited into the core magnetospheric plasma.

Electron pitch angle (Dαα) and momentum (Dpp) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in Dαα and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than Dαα coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than Dαα coefficients for the case n ≠ 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of Dαα coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle 10° and Landau resonance. Further, in ECH waves, the banded structures appear for electron energies ≥1 keV, and for whistler mode chorus waves, structures appear for energies >2 keV at L = 4.6 and above 200 eV for L = 6.8. The results obtained in the present work will be helpful in the study of diffusion curves and will have important consequences for diffuse aurora and pancake distributions.

The precipitation of high-energy magnetospheric electrons (E similar to 600 eV-10 KeV) in the diffuse aurora contributes significant energy flux into the Earth's ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, similar to 700-800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700-800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region.

There are two main theories for the origin of the diffuse auroral electron precipitation: first, pitch angle scattering by electrostatic electron cyclotron harmonic (ECH) waves, and second, by whistler mode waves. Precipitating electrons initially injected from the plasma sheet to the loss cone via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These secondary electrons can escape back to the magnetosphere, become trapped on closed magnetic field lines, and deposit their energy back to the inner magnetosphere. ECH and whistler mode waves can also move electrons in the opposite direction, from the loss cone into the trap zone, if the source of such electrons exists in conjugate ionospheres located at the same field lines as the trapped magnetospheric electron population. Such a situation exists in the simulation scenario of superthermal electron energy interplay in the region of diffuse aurora presented and discussed by Khazanov et al. (2014) and will be quantified in this paper by taking into account the interaction of secondary electrons with ECH waves.

The present study is aimed at resolving the issue of pitch-angle diffusion by whistler mode waves near Ganymede and to understand the interaction of Ganymede with magnetosphere of Jupiter. A new electron distribution function, which is a combination of Maxwellian and kappa loss-cone distribution, is used to calculate whistler mode wave growth rates. The distribution function is fitted to observed distribution near Ganymede. Wave growth rates have been used to obtain bounce-averaged pitch-angle diffusion coefficients along the field line connecting Ganymede and Jupiter. Variations of electron density and magnetic field along the particle bounce trajectory and a non dipolar field have been taken into account. Pitch-angle variation of diffusion coefficients is parameterized in a simple form ~Dο(sinα)p. Do is diffusion coefficient (independent of pitch angle). The calculated energy dependence of diffusion coefficients (Do) is in good agreement with observed energy dependence of coefficient Do. Wave magnetic field ~16pT is required to match observed and calculated diffusion coefficients. The exponent p takes values from ~1 to 4 for electron energies 15keV to 1MeV, respectively. It is found that contribution of Ganymede interaction region to pitch-angle scattering is quite small (~4% to 20%). Further analysis of Galileo energetic particle detector (EPD) and plasma wave data or new particle and wave data near Ganymede from JUNO mission to Jupiter are necessary to confirm the findings of present work.

Jupiter’s moon—Ganymede—is the largest satellite in our solar system. Galileo spacecraft made six close flybys to explore Ganymede. More information was acquired about particle population, magnetic field and plasma waves during these encounters. In this paper, our aim is to study the generation of electrostatic electron cyclotron harmonic (ECH) emissions in the vicinity of Ganymede using the observed particle data. The calculated ECH wave’s growth rates are analyzed in the light of observations of plasma waves along the path of Galileo near Ganymede. Dispersion relation for electrostatic mode is solved to obtain the temporal growth rates. A new electron distribution function, fitted to distribution observed near Ganymede, is used in the calculations. A parametric study is performed to evaluate the effect of loss-cone angle and the ratio of plasma to gyro-frequency on growth rates. It is found that ECH waves growth rates generally decrease as the loss-cone angle is increased. However, the ratio plasma to gyro-frequency has almost no effect on the growth rates. These parameters vary considerably along the Galileo trajectory near Ganymede. This is the first study which relates the occurrence of ECH waves with the particle and magnetic field data in the vicinity of Ganymede. The study of ECH wave growth rate near Ganymede is important for the calculation of pitch angle scattering rates of low-energy electrons and their subsequent precipitation into the thin atmosphere of Ganymede producing ultraviolet emissions. Results of the present study may also be relevant for the upcoming JUNO and JUICE missions to Jupiter.

Bounce-averaged pitch angle diffusion rates of electrons due to whistler mode waves have been calculated in the Jupiter's magnetosphere. Variations of electron density, magnetic field, wave intensity and upper cut-off frequency along the particle bounce trajectory have been taken into account. Field line tracing is performed to obtain the loss-cone size associated with the VIP 4 magnetic field model including the external field due to azimuthal current sheet. Numerical calculations have been carried out at L shells 10, 12, 15, 18, and 20. The longitudinal variations of electron energy precipitation into the atmosphere leading to diffuse aurora have been modelled. It is found that observed wave amplitudes at L <= 15 are insufficient to put electrons on strong pitch angle diffusion whereas at L=18 and 20 electrons of energies <= 30 keV can be put on strong diffusion. At L=10 electron energy precipitation supports auroral brightness of 25 kR in the northern and 36 kR in the southern hemisphere at west longitude similar to 10-60 degrees. At shells L=12 and 15 auroral brightness less than 10 kR is obtained. This is in accord with Voyager observation of jovian UV aurora just beyond the In torus (7-12R(J)). At L=18 maximum auroral brightness 73 kR in the northern hemisphere at west longitude of 16 degrees and 30 kR in the southern hemisphere for west longitudes <= 50 degrees are obtained. This is in agreement with the diffuse auroral brightness measured by Hubble Space Telescope (HST). Observations of longitudinal variation of diffuse auroral brightness are, however, required to ascertain the present findings. (C) 2013 Published by Elsevier Inc.

Pitch-angle diffusion coefficients of electrons have been calculated for resonant interaction with electrostatic electron-cyclotron harmonic (ECH) waves using quasi linear diffusion theory. Calculations have been performed for the planets Earth and Jupiter at three radial distances for each planet. Electron precipitation fluxes have also been calculated and compared with observed fluxes. At Earth, electrons of energy ≤200 eV may be put on strong diffusion at L = 10. At lower L values, observed ECH wave amplitudes are insufficient to put electrons on strong diffusion. At Jupiter, electrons can be put on strong diffusion at all L values. However, the energy of electrons which may be put on strong diffusion decreases from about 1 keV at L = 7 to ~100 eV at L = 17. It is concluded that ECH waves may be partly responsible for diffuse auroral precipitation of low energy electrons at Jupiter for lower L values. At Earth contribution of ECH waves to diffuse aurora is quite small.

Bounce-averaged pitch angle diffusion coefficients of electrons due to resonant interaction with electrostatic electron cyclotron harmonic (ECH) and whistler mode waves have been calculated. Temporal growth rates obtained by solving the appropriate dispersion relation have been used to represent the distribution of wave energy with frequency. Calculations have been performed at two spatial locations L=4.6 and L=6.8. The results obtained suggest that ECH waves can put electrons on strong pitch angle diffusion at both spatial locations. However, at L=4.6, electrons with energy <100eV and at L=6.8 electrons with energy up to ∼500eV can be put on strong diffusion contributing to diffuse auroral precipitation. Whistler mode waves can put electrons of energy ≤5keV on strong pitch angle diffusion at L=6.8 whereas at L=4.6 observed wave fields are insufficient to put electrons on strong diffusion. ECH waves contribute up to 17% of the total electron energy precipitation flux due to both ECH and whistler mode waves. A case study has been performed to calculate pitch angle diffusion coefficients using Gaussian function to represent wave energy distribution with frequency. It is found that, for electron energy <500eV, the calculated diffusion coefficients using Gaussian function to represent ECH wave energy distribution are several orders of magnitude smaller or negligible as compared to diffusion coefficients calculated by temporal growth rates. However, the calculated pitch angle diffusion coefficients using Gaussian function for whistler mode wave energy distribution are in very good agreement with diffusion coefficients calculated by temporal growth rates. It is concluded that representing the ECH wave energy distribution with frequency by a Gaussian function grossly underestimates the low energy (<500eV) electron precipitation flux due to ECH waves.

Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH) waves in the magnetospheres of Earth, Jupiter, Saturn, Uranus and Neptune. Calculations have been performed at two radial distances of each planet. It is found that observed wave electric field amplitudes in the magnetospheres of Earth and Jupiter are sufficient to put electrons on strong diffusion in the energy range of less than 100 eV. However, for Saturn, Uranus and Neptune, the observed ECH wave amplitude are insufficient to put electrons on strong diffusion at any radial distance.

We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures.

Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH) waves using quasilinear diffusion theory. Unlike previous calculations, the parallel group velocity has been included in this study. Further, ECH wave intensity is expressed as a function of wave frequency and wave normal angle with respect to ambient magnetic field. It is found that observed wave electric field amplitudes in Earth's magnetosphere are sufficient to set electrons on strong diffusion in the energy ranges of a few hundred eV. However, the required amplitudes are larger than the observed values for keV electrons and higher by about a factor of 3 compared to past calculations. Required electric field amplitudes are smaller at larger radial distances. It is concluded that ECH waves are responsible for diffuse auroral precipitation of electrons with energies less than about 500 eV. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3264735]

Whistler-mode instability in the magnetospheres of the outer planets Uranus and Neptune is investigated using an anisotropic kappa loss-cone distribution and comparisons have been made with the observations made by Voyager 2. Normalized temporal growth rates have been evaluated numerically at two representative radial distances at each planet. Parametric studies have been performed by changing plasma parameters: cold and hot electron densities, hot electron temperature and temperature anisotropy. It is found that whistler-mode emissions observed at lower radial distances cannot be reproduced in our calculations. Electron pitch-angle diffusion and energy diffusion coefficients have been obtained using the calculated growth rates. The present calculations show that electrons of energy above about 20keV may be able to precipitate into the planetary atmospheres of both planets. Present studies should be helpful in making estimates on scattering properties of whistler-mode waves and thus contribute to a better understanding of the auroral activity in the planetary atmospheres.

Electrostatic electron–cyclotron harmonic (ECH) instability in the magnetospheres of the outer planets: Jupiter, Saturn, Uranus and Neptune is investigated using a kappa distribution with loss-cone for energetic electrons in the tail of the distribution function. We use a particle distribution function, which is a superposition of cold (Maxwellian) and hot suprathermal (kappa) electrons in conformity with the observations. A linear instability analysis is used without making any further approximation. Normalized temporal growth rates have been obtained at two radial distances for each planet. Peak growth rates have also been studied as a function of the cold electron density (nc), hot electron density (nh), cold electron temperature (Tc), hot electron temperature (Th) and radial distance to the planet (R). Calculated normalized temporal growth rates for ECH bands are found highest at Uranus. The relative amplitudes of the ECH bands and the number of bands strongly depend on the angle (ψ) between the wave normal and the ambient magnetic field. Frequency within the band shifts in general to a higher value as the angle ψ is reduced. Results of our calculations are discussed in the light of observations of ECH bands at outer planets.

this article it is shown that these laser-accelerated energetic particles are finding applications inthe traditional areas of nuclear physics. Recent experimental results from an exciting programmeof laser-induced nuclear physics are presented and discussed

Abstract.The components of the dielectric tensor for the distribution function given by Leubner and Schupfer have been obtained. The effect of the loss-cone index appearing in the particle distribution function in a hot magnetized plasma has been studied. A case study has been performed to calculate temporal growth rates of Bernstein waves using the distribution function given by Summers and Thorne and Leubner and Schupfer. The effect of the loss-cone index on growth rates is found to be quite different for the two distribution functions.

Components of the dielectric tensor are obtained for a kappa-Maxwellian velocity distribution with loss-cone feature for a hot, infinite, homogeneous plasma immersed in a uniform magnetic field. Expansions valid for small propagation angle (angle between the wave vector and the ambient magnetic field) are given for the elements of the dielectric tensor.