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Kennel, C. F.

Publications and source records attributed to Kennel, C. F..

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Possibility of detecting magnetospheric radio bursts from Uranus and Neptune

The intensity of magnetospheric radio bursts (MRBs) is scaled to solar-wind input into planetary magnetospheres and the frequency of emission is scaled to polar surface magnetic-field strength in order to estimate the possibility of detecting MRBs from Uranus and Neptune. A scaling law is derived which relates the ratio of power radiated in MRBs to the solar-wind input for earth, Jupiter, and Saturn. Power-flux spectra of MRBs from these three planets are plotted, and it is shown that Jupiter and Saturn may radiate 1% to 5% of the solar-wind energy input into their magnetospheres. The properties of MRBs from Uranus and Neptune are estimated by assuming a conversion efficiency of 1% to 5%, a bandwidth of half the peak frequency, and conformity of Uranus' and Neptune's dipole moments with the magnetic Bode's law. Based on the results, it is suggested that detection of MRBs from these two planets may be a reasonable cruise-mode radio-astronomy objective on future missions to the outer solar system.

Kennel, C. F.↗
NASA NTRS1975

Linear theory of equatorial spread F

A fluid dispersion relation for the drift and interchange (Rayleigh-Taylor) modes in a collisional plasma forms the basis for a linear theory of equatorial spread F. The collisional-drift-mode growth rate will exceed the growth rate of the Rayleigh-Taylor mode at short perpendicular wavelengths and density-gradient scale lengths. The drift mode can grow on the top-side as well as the bottom-side density gradients. It is concluded that below the F peak where spread F predominates, both the drift and Rayleigh-Taylor modes contribute to the total spread F spectrum, with the Rayleigh-Taylor mode dominating at long and the drift mode at short perpendicular wavelengths above the ion Larmor radius.

Hudson, M. K.↗
NASA NTRS1975

On the detection of magnetospheric radio bursts from Uranus and Neptune

Earth, Jupiter, and Saturn are sources of intense but sporadic bursts of electromagnetic radiation or magnetospheric radio bursts (MRB). The similarity of the differential power flux spectra of the MRB from all three planets is examined. The intensity of the MRB is scaled for the solar wind power input into a planetary magnetosphere. The possibility of detecting MRB from Uranus and Neptune is considered.

Kennel, C. F.↗
NASA NTRS1975

What we have learned from the magnetosphere

Three significant discoveries resulting from recent studies of earth's magnetosphere are discussed: (1) the central role of magnetic-field-line reconnection in determining the topology, geometry, and dynamics of the magnetosphere; (2) the realization that auroral arcs result from coupling of solar-wind stresses to the ionosphere and neutral atmosphere; and (3) the role of plasma turbulence in affecting both the microscopic state and macroscopic observables of the magnetospheric plasma. Magnetic-field-line reconnection is described in terms of Dungey's (1961) model of the magnetosphere, a simple picture of magnetic-substorm evolution is outlined, and questions concerning the reconnection rate are considered. The production of aurorae by field-aligned electron beams is examined, and an analogy is made between earth's magnetosphere and that of a pulsar with aligned dipole and spin axes. Plasma-turbulence problems are reviewed which concern anomalously fast electron and proton losses from the Van Allen belts, whistler-electron interactions, and anomalous resistance in auroral arcs. The Pioneer 10 encounter with Jupiter's magnetosphere is briefly noted.

Kennel, C. F.↗
NASA NTRS1975

Relativistic nonlinear plasma waves in a magnetic field

Five relativistic plane nonlinear waves were investigated: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an 'electron-positron' plasma leads to equations which have the form of a one-dimensional potential well. The solutions indicate that a large-amplitude superluminous wave determines the average plasma properties.

Kennel, C. F.↗
NASA NTRS1975

Is Jupiter's magnetosphere like a pulsar's or earth's

Two possible models of Jupiter's magnetosphere are compared: a pulsar-like radial-outflow model and an earth-like convection model. For the radial-outflow model, Pioneer 10 data are used to estimate the total particle and energy fluxes which must be provided by Jupiter (or its magnetosphere within the Alfven radius) to power the outflow. The convection model is considered with emphasis on field-line reconnection, convection flow time, and the location of Jupiter's magnetopause and plasmapause. The imposition of corotation on Jupiter's ionosphere, magnetosphere, and upper atmosphere is investigated in terms of an aligned rotator with either type of magnetosphere. It is concluded that: (1) Jupiter's convection flow is likely to be super-Alfvenic in its outer magnetosphere, (2) Jupiter may have earth-like magnetopauses near local dawn during substorms, (3) the angular-momentum flux that can diffuse upward through Jupiter's polar-cap atmospheres seems insufficient to impose corotation upon a radial outflow or convective return flow, and (4) neither model can be definitively accepted.

Kennel, C. F.↗
NASA NTRS1975

The electromagnetic interchange mode in a partly-ionized collisional plasma

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift, and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange mode is noted: coupling to the intermediate Alfven mode is strongly stabilizing for finite perturbations of the magnetic field. Both ion-viscous and ion-neutral stabilization are included; and it is found that collisions destroy the FLR (finite Larmor radius) cutoff at short perpendicular wavelengths.

Hudson, M. K.↗
NASA NTRS1974

High density constraint on the entropy instability

The entropy instability squared is a nonisothermal effect which is eliminated by parallel ion pressure at high densities (k sub z lambda sub e 1/2 sq root of m/M), reducing previous growth rate estimates and the range of unstable parameters.

Hudson, M. K.↗
NASA NTRS1974

The electromagnetic interchange mode in a partially ionized collisional plasma

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.

Hudson, M. K.↗
NASA NTRS1974

The collisional drift mode in a partially ionized plasma

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.↗
NASA NTRS1974

Is Jupiter's magnetosphere like a pulsar's or earth's?

The application of pulsar physics to determine the magnetic structure in the planet Jupiter outer magnetosphere is discussed. A variety of theoretical models are developed to illuminate broad areas of consistency and conflict between theory and experiment. Two possible models of Jupiter's magnetosphere, a pulsar-like radial outflow model and an earth-like convection model, are examined. A compilation of the simple order of magnitude estimates derivable from the various models is provided.

Kennel, C. F.↗
NASA NTRS1974

Stably trapped proton fluxes in the Jovian magnetosphere

A model of the energetic proton fluxes in the Jovian magnetosphere is constructed based on the inward radial diffusion of protons from the solar wind and the plasma turbulent precipitation loss of protons from the radiation belts. Outside 12 Jovian radii the proton fluxes follow a loss-free radial diffusion profile. Inside 12 Jovian radii the proton fluxes should be near the stably trapped limit flux set by convective marginal stability to the electromagnetic ion cyclotron wave and the quasi-electrostatic ion loss-cone wave.

Coroniti, F. V.↗
NASA NTRS1974

On the marginally stable saturation spectrum of unstable type I equatorial electrojet irregularities

Formulation of a self-consistent convective nonlinear theory of type I irregularities in the equatorial electrojet. It is found that a combination of three mechanisms - convective amplification, quasi-linear polarization electric field reduction, and nonlinear particle orbit diffusion damping - accounts for radar backscatter observations of a ubiquitous marginally stable (or 'constant ion-acoustic Doppler shift') saturation spectrum better than any of the three mechanisms treated separately. In particular, no spatially homogeneous theory without wave refraction can account for the observations. Wave refraction alone or with quasi-linear polarization electric field reduction is also inadequate. Wave refraction, quasi-linear polarization reduction, and particle orbit diffusion theory appear to account for type I observations at radar elevation angles less than 60 deg. Vertical type I backscatter cannot be explained without modifying the present laminar electrojet model.

Lee, K.↗
NASA NTRS1973

Cosmic-ray generation by pulsars

Electromagnetic and particle energy fluxes are equipartitioned in a superrelativistic plasma wave. The consequences for cosmic-ray acceleration by pulsars are investigated.

Kennel, C. F.↗
NASA NTRS1973

Finite beta drift Alfven instability

We propose a means by which the theory of drift instabilities can be extended to plasmas of arbitrary beta. We then concentrate on the drift Alfven instability driven by an electron temperature gradient, proposed by Coroniti and Kennel (1970) to be a source of Pi 1 micropulsations on auroral lines of force. Even at relatively low beta the full finite beta theory differs considerably from previous low beta theories and produces better agreement with observation.

Chance, M. S.↗
NASA NTRS1973

Convective amplification of type I irregularities in the equatorial electrojet.

Wave propagation and refraction of 'type I' irregularities in the equatorial electrojet are investigated. Quantitative calculation of wave refraction in a model electrojet shows that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upward in the upper electrojet and downward in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray-path integrated wave growth show that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. It is therefore concluded that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic speed.

Lee, K.↗
NASA NTRS1973

Can the ionosphere regulate magnetospheric convection.

A simple model is outlined that relates the dayside magnetopause displacement to the currents feeding the polar cap ionosphere, from which the ionospheric electric field and the flux return rate may be estimated as a function of magnetopause displacement. Then, flux conservation arguments make possible an estimate of the time scale on which convection increases.

Coroniti, F. V.↗