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NASA NTRS2007

Reply to "Comment on 'A Self-Consistent Model of the Interacting Ring Current Ions and Electromagnetic Ion Cyclotron Waves, Initial Results: Waves and Precipitation Fluxes' and 'Self-Consistent Model of the Magnetospheric Ring Current and Propagating Electromagnetic Ion Cyclotron Waves: Waves in Multi-Ion Magnetosphere' by Khazanov et al. et al."

It is well-known that the effects of electromagnetic ion cyclotron (EMIC) waves on ring current (RC) ion and radiation belt (RB) electron dynamics strongly depend on such particle/wave characteristics as the phase-space distribution function, frequency, wavenormal angle, wave energy, and the form of wave spectral energy density. The consequence is that accurate modeling of EMIC waves and RC particles requires robust inclusion of the interdependent dynamics of wave growth/damping, wave propagation, and[ particles. Such a self-consistent model is being progressively developed by Khazanov et al. [2002, 2006, 2007]. This model is based on a system of coupled kinetic equations for the RC and EMIC wave power spectral density along with the ray tracing equations. Thome and Home [2007] (hereafter referred to as TH2007) call the Khazanov et al. [2002, 2006] results into question in their Comment. The points in contention can be summarized as follows. TH2007 claim that: (1) "the important damping of waves by thermal heavy ions is completely ignored", and Landau damping during resonant interaction with thermal electrons is not included in our model; (2) EMIC wave damping due to RC O + is not included in our simulation; (3) non-linear processes limiting EMIC wave amplitude are not included in our model; (4) growth of the background fluctuations to a physically significantamplitude"must occur during a single transit of the unstable region" with subsequent damping below bi-ion latitudes,and consequently"the bounce averaged wave kinetic equation employed in the code contains a physically erroneous 'assumption". Our reply will address each of these points as well as other criticisms mentioned in the Comment. TH2007 are focused on two of our papers that are separated by four years. Significant progress in the self-consistent treatment of the RC-EMIC wave system has been achieved during those years. The paper by Khazanov et al. [2006] presents the latest version of our model, and in this Reply we refer mostly to this paper.

Khazanov, G. V.↗

NASA NTRS1982

Direct measurements of plasma characteristics in space-simulation beam-plasma interactions

Recent laboratory investigations of space-simulated electron-beam-plasma interactions are discussed. The plasma has been characterized with respect to its spatial distributions in density, temperature, and density fluctuation power spectra. The latter results have been further classified in terms of amplitude and spectral distributions. The overall results include: (1) detailed radial profiles of plasma density as a function of beam parameters; (2) the association of low-frequency large amplitude fluctuations with ion acoustic, ion cyclotron, and drift-wave modes; (3) the identification and spatial mapping of suprathermal electrons in the beam core; and (4) the experimental definition of a density-dependent criterion for the ignition of the beam-plasma-discharge.

Szuszczewicz, E. P.↗

NASA NTRS1994

Excitation of high-frequency electromagnetic waves by energetic electrons with a loss cone distribution in a field-aligned potential drop

The electron cyclotron maser instability (CMI) driven by momentum space anisotropy (df/dp (sub perpendicular) greater than 0) has been invoked to explain many aspects, such as the modes of propagation, harmonic emissions, and the source characteristics of the auroral kilometric radiation (AKR). Recent satellite observations of AKR sources indicate that the source regions are often imbedded within the auroral acceleration region characterized by the presence of a field-aligned potential drop. In this paper we investigate the excitation of the fundamental extraordinary mode radiation due to the accelerated electrons. The momentum space distribution of these energetic electrons is modeled by a realistic upward loss cone as modified by the presence of a parallel potential drop below the observation point. On the basis of linear growth rate calculations we present the emission characteristics, such as the frequency spectrum and the emission angular distribution as functions of the plasma parameters. We will discuss the implication of our results on the generation of the AKR from the edges of the auroral density cavities.

Fung, Shing F.↗

NASA NTRS2000

Roles Played by Electrostatic Waves in Producing Radio Emissions

Processes in which electromagnetic radiation is produced directly or indirectly via intermediate waves are reviewed. It is shown that strict theoretical constraints exist for electrons to produce nonthermal levels of radiation directly by the Cerenkov or cyclotron resonances. In contrast, indirect emission processes in which intermediary plasma waves are converted into radiation are often favored on general and specific grounds. Four classes of mechanisms involving the conversion of electrostatic waves into radiation are linear mode conversion, hybrid linear/nonlinear mechanisms, nonlinear wave-wave and wave-particle processes, and radiation from localized wave packets. These processes are reviewed theoretically and observational evidence summarized for their occurrence. Strong evidence exists that specific nonlinear wave processes and mode conversion can explain quantitatively phenomena involving type III solar radio bursts and ionospheric emissions. On the other hand, no convincing evidence exists that magnetospheric continuum radiation is produced by mode conversion instead of nonlinear wave processes. Further research on these processes is needed.

Cairns, Iver H.↗

NASA NTRS1991

Kilometric radio waves generated along auroral field lines observed by ground facilities - A theoretical model

A theory of generation of radio waves observed by ground-based facilities in the frequency range 150-700 kHz is discussed. This work is a continuation of an earlier discussion (Wu et al., 1989) in which it was proposed that the trapped electrons along the auroral field lines can lead to a cyclotron instability which amplifies the whistler waves observed at ground level. The objective of the present study is to investigate the propagation effect on the wave amplification and to examine whether the proposed mechanism is indeed viable.

Ziebell, L. F.↗

NASA NTRS1994

Localized injection of large-amplitude Pc 1 waves and electron temperature enhancement near the plasmapause observed by DE2 in the upper ionosphere

The relation between electron temperature enhancement and large amplitude Pc 1 wave injections in the upper ionosphere is investigated using the data obtained by the Dynamics Explorer 2 spacecraft. Results can be summarized as follows: (1) The region of the temperature enhancement coincides with that of the wave injection which is latitudinally very narrow (less than 100 km) in comparison with the wavelength along the ambient magnetic field (several hundred kilometers). (2) The duration of the wave injection (or the temperature enhancement) seems to be less than a few hours even under quiet geomagnetic conditions, and/or the injection seems to be very localized, not only latitudinally, but also longitudinally. (3) The appearance and the magnitude of temperature enhancement depend on both the wave amplitude and the satellite altitude. (4) Two of the 22 events that were analyzed show a clear enhancement of low-energy electron flux (5 to 30 eV) at the wave injection, and the flux is field-aligned both downward and upward. The region of the temperature enhancement coincides with that of the downward electron flux. From these results, it is suggested that the temperature enhancement which accompanies large-amplitude waves with Pc 1 pulsation frequencies (0.2 to 5 Hz) is caused by the direct acceleration of thermal electrons at low altitudes by the parallel electric field (0.01 to 0.001 mV/m) of the ion-cyclotron waves (kinetic Alfven waves) having an oblique wave normal.

Iyemori, T.↗

NASA NTRS2011

The Roles of Transport and Wave-Particle Interactions on Radiation Belt Dynamics

Particle fluxes in the radiation belts can vary dramatically during geomagnetic active periods. Transport and wave-particle interactions are believed to be the two main types of mechanisms that control the radiation belt dynamics. Major transport processes include substorm dipolarization and injection, radial diffusion, convection, adiabatic acceleration and deceleration, and magnetopause shadowing. Energetic electrons and ions are also subjected to pitch-angle and energy diffusion when interact with plasma waves in the radiation belts. Important wave modes include whistler mode chorus waves, plasmaspheric hiss, electromagnetic ion cyclotron waves, and magnetosonic waves. We investigate the relative roles of transport and wave associated processes in radiation belt variations. Energetic electron fluxes during several storms are simulated using our Radiation Belt Environment (RBE) model. The model includes important transport and wave processes such as substorm dipolarization in global MHD fields, chorus waves, and plasmaspheric hiss. We discuss the effects of these competing processes at different phases of the storms and validate the results by comparison with satellite and ground-based observations. Keywords: Radiation Belts, Space Weather, Wave-Particle Interaction, Storm and Substorm

Fok, Mei-Ching↗

NASA NTRS1990

Relaxation of the loss-cone by quasi-linear diffusion of the electron-cyclotron maser instability in the solar corona

A self-consistent numeric two-dimensional code using kinetic-wave particle equations has been developed and applied to the maser dynamics of the solar corona. Time histories generated by the code reveal details of the evolution of the linear phase, the saturation and subsequent relaxation of the loss cone. Quantitative values are obtained for the saturation time, the amount of the converted free energy, the critical wave energy level for onset of maser diffusion, the velocity and pitch angle range of the resonant particles, and the relative importance of the different magnetoionic modes and harmonics. A wide range of initial conditions is covered by varying the loss-cone distribution and the ambient cold plasma parameters.

Aschwanden, Markus J.↗

NASA NTRS2016

Van Allen Probes, THEMIS, GOES, and Cluster Observations of EMIC Waves, ULF Pulsations, and an Electron Flux Dropout

We examined an electron flux dropout during the 12-14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12-13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ electromagnetic ion cyclotron (EMIC) waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13-14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst<100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.

Sigsbee, K.↗

NASA NTRS1990

Production of electron conics by stochastic acceleration parallel to the magnetic field

Electron conics are enhancements in the electron flux at the edges of the electron loss cone. Such enhancements are a common feature in the electron distribution in the auroral zone. In analogy with ion conics, it has been suggested that electron conics are produced by waves which accelerate electrons perpendicular to the magnetic field. However, using a test particle simulation of the electron distribution it is shown that electron conics can be produced purely by stochastic acceleration of the electrons parallel to a dipole magnetic field. A possible wave mode that can produce parallel acceleration is the Alfven-ion cyclotron mode that has recently been shown to modulate the high energy part of the inverted-V electron distribution.

Temerin, Michael A.↗

NASA NTRS1976

Whistler mode plasma waves observed on Electron Echo 2

Observations of whistler-mode waves associated with beams of electrons injected into the ionosphere are reported. The measurements are from the plasma-wave experiments carried on the Electron Echo 2 sounding rocket launched on September 24, 1972. Over 2000 electron injections were made with durations of 8 ms and 64 ms and pitch angles from 0 to 180 deg. The electric field receivers carried on the ejected nose cone observed strong whistler waves in the range from less than 100 kHz up to the electron cyclotron frequency of 1400 kHz. The whistler characteristics fall into four distinct types depending on pitch angle and gun energy. Both frequency and amplitude showed strong dependence on time from the start of the pulse and pitch angle. Cases of enhancement at the leading edge of a gun pulse, growth during a pulse, and echoes after the end of a pulse were all observed.

Monson, S. J.↗

NASA NTRS1979

A theory of the terrestrial kilometric radiation

During magnetospheric substorms, electrons with energies of about 1 keV are injected from the plasma-sheet region into the auroral region. A fraction of these energetic electrons can precipitate into the upper atmosphere, and the rest are reflected because of the mirror effect of the convergent geomagnetic field. It is found that these reflected electrons can result in the amplification of electromagnetic waves via a relativistic normal cyclotron resonance. This process may explain the recently discovered terrestrial kilometric radiation.

Wu, C. S.↗

NASA NTRS1979

Diffuse Jovian aurora influenced by plasma injection from Io

The paper demonstrates that the broad band of whistler-mode waves observed within the high density torus surrounding Io is consistent with electron cyclotron generation. Cyclotron resonant instability of Jovian energetic electrons is enhanced due to the lower resonant electron energy within the equatorial high density plasma torus surrounding the orbit of Io. The higher energy resonant electron scattering and the corresponding energetic electron lifetimes indicate that an efficient local acceleration process is required to replenish the precipitating relativistic electrons. Calculated energy deposition into the Jovian atmosphere should provide a dominant source of middle atmospheric ionization and excite a continuous band of diffuse auroral emission. It is suggested that the diffuse Jovian aurora should be influenced by the variable volcanic activity on Io which is thought to be an important source of plasma, since the cyclotron scattering process is strongly influenced by the ambient equatorial thermal plasma density.

Thorne, R. M.↗

NASA NTRS1977

Non-symmetric two-stream instability

A theoretical investigation is performed concerning the instability spectrum of quasi-electrostatic waves at shifted half-odd-integer values of the cyclotron frequency due to nonsymmetric counterstreaming electron beams. The beam velocities parallel and perpendicular to the static magnetic field are represented by double Dirac delta functions with no imposition of parameter limitations. Systematic consideration is given to the coupling between plasma modes and cyclotron modes as well as the coupling between cyclotron modes of the two beams that result in shifted half-odd-integer multiples of the cyclotron frequency. The general dispersion equation for quasi-electrostatic waves is analyzed, and plasma-cyclotron coupling in the nonsymmetric case is treated by deriving approximate analytical expressions for maximum growth rates and marginal stability. Exact numerical solutions in both frequency and wavenumber space are obtained and compared with the analytical expressions. Cyclotron-cyclotron coupling modes are treated in the same way, and the results for both types of coupling are compared. It is found that certain modes may be weakened or completely suppressed when the Bessel functions for specific plasma parameters vanish.

Cuperman, S.↗

NASA NTRS1972

Wave propagation in the magnetosphere of Jupiter

A systematic procedure is developed for identifying the spatial regimes of various modes of wave propagation in the Jupiter magnetosphere that may be encountered by flyby missions. The Clemmow-Mullaly-Allis (CMA) diagram of plasma physics is utilized to identify the frequency regimes in which different modes of propagation occur in the magnetoplasma. The Gledhill model and the Ioannidis and Brice model of the magnetoplasma are summarized, and configuration-space CMA diagrams are constructed for each model for frequencies from 10 Hz to 1 MHz. The distinctive propagation features, the radio noise regimes, and the wave-particle interactions are discussed. It is concluded that the concentration of plasma in the equatorial plane makes this region of vital importance for radio observations with flyby missions. Local radio noise around the electron cyclotron frequency will probably differ appreciably from its terrestrial counterpart due to the lack of field-line guidance. Hydromagnetic wave properties at frequencies near the ion cyclotron frequency and below will probably be similar to the terrestrial case.

Liemohn, H. B.↗

NASA NTRS1986

The generation of low-frequency electrostatic waves in association with auroral kilometric radiation

Observations of the electron distribution in the source region of auroral kilometric radiation (AKR) indicate that it can have positive gradients with respect to both v-perpendicular and v-parallel. It is shown that this type of distribution is unstable to both the electron cyclotron maser instability, which is responsible for AKR, and the bump-in-tail instability which generates electron acoustic waves in the hiss band. Simulations indicate that the two instabilities do not develop independently but compete for the available free energy due to the reduction in the positive gradients of the distribution caused by the quasi-linear diffusion associated with each instability. The dominant instability depends on the ratio of the density of the energetic electrons n(E) to that of the background electrons n(b). For n(E)/n(b) greater than about 1, the maser instability dominates, and the bump-in-tail instability is suppressed, whereas the reverse is true if n(E)/n(b) is smaller than about 1. Comparison with observations indicates that probably n(E)/n(b) is greater than about 1 in the source region of AKR.

Winglee, R. M.↗

NASA NTRS1972

A resonant instability of model proton radiation belts in the Jovian magnetosphere

The ion cyclotron instability and characteristics of the ion cyclotron wave are discussed. A mathematical perturbation technique is applied to the dispersion relations, and the results are applied to the case of propagation parallel to the magnetic field. The ion cyclotron wave is determined in its damping and growth characteristics by resonant protons and electrons, found in momentum space on resonant surfaces. In the relativistic case the resonant surfaces are hyperbolas of revolution around the magnetic field, and protons can have a stabilizing effect. Instability rates are calculated for the region in the equatorial plane with the Ioannidis and Brice density model. The upper limit of proton flux which gives an energy density of the same order of magnitude as the magnetic field energy density is obtained. The upper limit is plotted with respect to distance from Jupiter and the minimum resonant energy contributing to the instability is also plotted.

Neubauer, F. M.↗

NASA NTRS1978

Three-dimensional plasma measurements within the earth's magnetosphere

Magnetospheric measurements of three-dimensional velocity distributions for positive ions and electrons in the energy range from 1 eV to 45 keV are reported which were obtained with quadrispherical Lepedeas on ISEE 1 and 2. The instrumentation is briefly described, and an extension of energy-time spectrograms to three-dimensional summaries via the use of ancillary energy-spin phase spectrograms for multiple analyzers is outlined. Macroscopic plasma parameters for two crossings of the dayside magnetopause are presented, along with a preliminary evaluation of the kinematical motions of low-energy charged particles within the terrestrial ring current. Nonmonotonic electron velocity distributions presumably related to the generation of electron cyclotron harmonic instabilities are examined. The possible signature of diffusion driven by electrostatic waves is considered, and velocity distributions of positive ions in the dawn magnetotail are investigated.

Frank, L. A.↗