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  • GEOPHYSICS  (17)
  • COMMUNICATIONS AND RADAR  (1)
  • 1990-1994  (8)
  • 1975-1979  (10)
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  • GEOPHYSICS  (17)
  • COMMUNICATIONS AND RADAR  (1)
Years
Year
  • 1
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    The control of the magnetosphere by power line radiation (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Evidence is presented that radiated power line harmonics leak into high-altitude regions of the magnetosphere with sufficient intensity to control the starting frequencies of chorus emissions. OGO-3 data from three passes show that the starting frequencies of all measurable chorus emissions were within a few hertz of power line harmonics. It is also found that emissions detected over Western Europe were controlled by harmonics of 50 Hz; over the eastern United States and Canada by 60 Hz; and along the Alaska-New Zealand meridian by harmonics of both 50 and 60 Hz. These results indicate that man-made VLF noise plays an important role in the generation of chorus, one of the commonly observed forms of wave activity in the outer magnetosphere.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 84; June 1
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  • 2
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    VLF line radiation in the earth's magnetosphere and its association with power system radiation (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: In a recent experiment, discrete VLF emissions from the magnetosphere were triggered by a transmitter at Siple Station in Antarctica. Spectrograms of these signals as received at the conjugate point, Roberval, Quebec, showed changes in slope, entrainments, and cutoffs at frequencies (several kilohertz) close to the harmonic induction lines from the local 60-Hz power system. This observation led to the suggestion that harmonic radiation from the power system enters the magnetosphere and interacts with the triggered emissions. New evidence supporting this suggestion has been found in spectrograms of simultaneous recordings made at Roberval and at Siple Station in Antarctica. It is shown that line radiation, near harmonics of 60 Hz, travels along the earth's magnetic field in the whistler mode and is received in the conjugate hemisphere at Siple Station. Echoing of the line radiation between Siple and Roberval is often observed. The magnetospheric lines are usually shifted in frequency by 20-30 Hz with respect to the adjacent induction line, but their spacings are near 120 Hz. They may trigger and cut off emissions as do signals from VLF transmitters.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Journal of Geophysical Research; 80; Nov. 1
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  • 3
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    Magnetospheric chorus - Amplitude and growth rate (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A new study of the amplitude of magnetospheric chorus with 1966-1967 data from the Stanford University/Stanford Research Institute VLF receivers on Ogo 1 and Ogo 3 has confirmed the band-limited character of magnetospheric chorus in general and the double-banding of near-equatorial chorus. Chorus amplitude tended to be inversely correlated with frequency, implying lower intensities at lower L values. Individual chorus emissions often showed a characteristic amplitude variation, with rise times of 10 to 300 ms, a short duration at peak amplitude, and decay times of 100 to 3000 msec. Growth was often approximately exponential, with rates from 200 to nearly 2000 dB/sec. Rate of change of frequency was found in many cases to be independent of emission amplitude, in agreement with the cyclotron feedback theory of chorus (Helliwell, 1967, 1970).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; Aug. 1
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  • 4
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    Nonlinear pitch angle scattering of energetic electrons by coherent VLF waves in the magnetosphere (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A study is made of nonlinear cyclotron resonance wave-particle interaction in the magnetosphere with attention to the pitch angle scattering of energetic electrons by coherent VLF whistler mode signals. A computer simulation of the full nonlinear equations of motions for energetic particles interacting with a longitudinal whistler mode wave in an inhomogeneous magnetosphere are used. The results are compared to those of a linear theory. Test electrons distributed in energy and pitch angle are used to simulate the full distribution of particles. The scattering of the test particles and their integration over energy and pitch angle yield the precipitated flux. The results suggest that coherent VLF waves significantly influence the dynamics and lifetimes of energetic electrons trapped in the magnetosphere and magnetic shells illuminated by the waves.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 83; July 1
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  • 5
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    Longitudinal variations of very-low-frequency chorus activity in the magnetosphere - Evidence of excitation by electrical power transmission lines (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The distribution of VLF chorus in the high-altitude magnetosphere as detected by the Ogo 3 satellite was investigated. Chorus occurrence frequency over 4,668 samples of 5 min of broadband data was computed for Northern Hemisphere bins of 10 deg by 10 deg in dipole invariant latitude and longitude. Peaks in activity were noted over Alaska, the eastern U.S. and Canada, western Europe, and western Siberia, and were shown not to be the result of biased sampling. It is suggested that power line radiation of only about 1 W or less at a given harmonic frequency may be sufficient to stimulate the observed chorus activity and that such power levels can be expected in industrial areas or from large distribution networks. Preliminary results show that chorus starting frequencies are highly correlated with 60 Hz harmonics in the American sector and with 50 Hz harmonics in the European sector.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 4; July 197
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  • 6
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    Siple station experiments on wave-particle interactions in the magnetosphere (1979)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Natural and controlled whistler-mode signals have been used to study nonlinear mechanisms of wave growth and wave-wave interactions (WWI) in the magnetosphere; three general classes of WWI (triggering, suppression, and entrainment) are identified and interpreted in terms of a model based on cyclotron resonance interaction. This model is also used to estimate the wave field intensity associated with different types of WWI. A new type of triggered emission, the band-limited impulse (BLI) is interpreted in terms of the switching of phase-bunched currents. In addition, an experiment to find a threshold for the excitation of the coherent wave instability is discussed, and observed VLF wave-induced transient bursts of X-rays, light and E-region ionization enhancements are considered with regard to a step function wave interacting with all resonant electrons in a given energy range.
    Keywords: GEOPHYSICS
    Type: Wave instabilities in space plasmas; Jul 31, 1978 - Aug 08, 1978; Helsinki; Finland
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  • 7
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    Effects of power line radiation into the magnetosphere (1979)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Observations of the effects of VLF power line radiation on whistler-mode waves in the magnetosphere are reviewed. High-altitude OGO-3 spectral data reveal evidence of enhanced chorus activity over populated regions starting at harmonics of the power-line frequencies. Low-altitude Ariel 3 measurements of 3.2 kHz noise intensity also indicate an enhancement of VLF activity over populated areas and their conjugates, however the relative importance of power line radiation, whistlers and spontaneous emissions is not known. The low-altitude polar-orbiting OGO-4 satellite also observed noise spectra at the harmonics of power line frequencies over industrial regions. Ground observations from Eights and Siple, Antarctica indicate that power line radiation effects on magnetospheric ducted paths peak at 3 kHz and near dawn, and exhibit a pronounced decrease on Sundays in the conjugate region, when power consumption is at a minimum. Experiments simulating power line radiation effects have also been performed. It is suggested that power line radiation effects magnetospheric activity by lowering the threshold for wave growth, with the localization of VLF sources acting to localize corresponding particle precipitation without necessarily affecting global average precipitation.
    Keywords: GEOPHYSICS
    Type: Wave instabilities in space plasmas; Jul 31, 1978 - Aug 08, 1978; Helsinki; Finland
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  • 8
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    Spacecraft observations of man-made whistler-mode signals near the electron gyrofrequency (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The reported investigation extends the range of whistler-mode wave observations to a wave frequency/electron gyrofrequency ratio of about 0.9, where an abrupt cutoff is observed. This cutoff can be explained entirely in terms of accessibility and hence, if there is damping, it must be limited to normalized frequencies above 0.9. In connection with a study of the behavior of the signal intensity, ray tracings were carried out at 80 kHz. The ray-tracing calculations were carried out with the aid of a computer program written by Walter (1969) and modified by Angerami (1970).
    Keywords: GEOPHYSICS
    Type: Radio Science; 12; Sept
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  • 9
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    Magnetospheric chorus - Occurrence patterns and normalized frequency (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Over 400 hours of continuous broadband data obtained by the OGO 3 satellite are analyzed to provide a statistically accurate description of band-limited (magnetospheric) chorus. Certain aspects of the chorus frequency distribution are interpreted in terms of a gyroresonant electron feedback model of generation. An example of high chorus activity during an outbound pass through the noon magnetosphere is examined in detail, the spectral complexity of some chorus is illustrated, and the diurnal variation of chorus occurrence is investigated. The frequency and bandwidth distributions of chorus are analyzed. The results indicate that chorus occurrence depends strongly on local time and dipole latitude, the general region of maximum chorus occurrence approximates the previously reported zone of 'hard' electron precipitation, and the normalized chorus frequency is strongly dependent on dipole latitude. It is shown how a change in the curvature of the whistler-mode refractive-index surface affects focusing of radiation along magnetic field lines and how interference can occur between modes with slightly different ray velocities. It is concluded that most magnetospheric chorus consists of rising emissions which are probably generated by gyroresonant electrons slightly off the equator.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science; 24; Nov. 197
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  • 10
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    The heating of suprathermal ions above thunderstorm cells (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We estimate ion heating in the topside ionosphere directly over thunderstorm cells. The primary heating is due to lower hybrid waves excited through linear mode coupling as intense electromagnetic (EM) whistler mode radiation from lightning is scattered from small scale (2 - 20 m) magnetic-field-aligned plasma density irregularities in the topside ionosphere. For typical radiated EM fields, we find that suprathermal H+ ions in the 6 eV and greater energy range can be heated by 20 to 40 eV as a result of a single lightning discharge. We also show how the number density of 6 eV and greater H(+) ions is enhanced by preheating resulting from the absorption of proton whistlers in the 500-1000 km altitude range. For lightning discharge rates of one or more per second over a 10 exp 4 sq km area, our model predicts a total energy gain for the H(+) ions of 400 eV to 2 KeV and a perpendicular ion flux of about 10 exp 5 to 10 exp 6/sq cm sec. These fluxes should be observable on low altitude spacecraft using presently available instrumentation.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8534); 20; 18; p. 1991-1994.
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