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  • GEOPHYSICS  (17)
  • 2010-2014
  • 2000-2004
  • 1980-1984  (17)
  • 1
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    Jikiken /EXOS-B/ observation of Siple transmissions (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Preliminary results of observations by the Japanese magnetospheric satellite Jikiken (EXOS-B) of Siple transmissions and VLF emissions triggered by the Siple signals are reviewed. The experiments discussed were carried out in July, August, and September of 1979 and in December 1979 and January 1980. Only four events concentrated within the period from August 14 to 18 were found in which triggered emissions were associated with Siple transmissions. The electron distributions observed on the equatorial crossing passes, when Siple triggered emissions were detected, suggest that the cyclotron resonance condition is satisfied for Siple signals and electrons of energy around 1 keV or less, provided the interaction region is inside the plasmapause. It is noted that if these emissions were generated outside the plasmapause, electron energies much higher than 10 keV would be necessary for the cyclotron interaction, which were above the range of the measurements. For the high latitude passes of August 14 and 17, the electron fluxes were found to be very small.
    Keywords: GEOPHYSICS
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    NASA TECHNICAL REPORTS
  • 2
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    The apparent spectral broadening of VLF transmitter signals during transionospheric propagation (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: ISIS 1 and 2 and ISEE 1 VLF/ELF electric field wave data indicate the existence of a novel phenomenon, in which initially narrow band upgoing signals from ground-based VLF transmitters undergo a significant spectral broadening as they propagate through the ionosphere and protonosphere, up to altitudes in the 600-3800 km range. For transmitter signals in the 10-20 kHz range, the spectral broadening can be as high as 10 percent of the input signal's nominal frequency. In many cases, the bandwidth of the spectrally broadened signals is a strong function of the electric dipole antenna orientation with respect to the local direction of the earth's magnetic field. The unusual dispersion in the components of the spectrally broadened pulses suggests that the spectral broadening may be due to a Doppler shift effect in which the initial signals scatter from irregularities in the F region and couple into quasi-electrostatic modes of short wave length.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; June 1
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    NASA TECHNICAL REPORTS
  • 3
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    EXOS-B/Siple station VLF wave-particle interaction experiments. I - General description and wave-particle correlations (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The EXOS-B/Siple Station joint experiment on the triggering of VLF emissions by man-made signals causing some form of wave-particle interactions in the magnetosphere is presented, and results concerning wave-particle correlations are reported. In situ measurements of both energetic electron flux and VLF waves were made near the meridian connecting Siple Station, Antarctica with Roberval, Quebec, Canada in campaigns during July through September, 1979 and December 1979 through January 1980 at times of VLF transmission from Siple. Strong observed signals were found to be well correlated with a pancake pitch angle distribution of 0.3 to 6.9-keV electrons, and to exhibit a positive linear growth rate. Artificially stimulated emissions were observed to be accompanied by large electron fluxes in all energy channels in the equatorial interaction region, although the measured pitch angle distribution was not highly anisotropic. Results may be interpreted by the amplification of Siple signals by the cyclotron instability due to high pitch angle anisotropy (pancake distribution) and the triggering of emissions in the presence of high electron fluxes with some anisotropy and a sufficiently strong signal.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 88; Jan. 1
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  • 4
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    Satellite measurements during Siple Station VLF wave-injection experiments (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: GEOPHYSICS
    Type: NASA-CR-173040 , NAS 1.26:173040
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  • 5
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    ISEE-1 observations in the magnetosphere of VLF emissions triggered by nonducted coherent VLF waves during VLF wave-injection experiments (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is noted that recent data from the ISEE-1 spacecraft indicate that VLF emissions triggered by conducted coherent VLF waves often possess spectral characteristics markedly different from those of emissions triggered by ducted waves. Emission triggering by nonducted waves is found to involve a strong path selectiveness. It is also established that emission triggering by nonducted waves can take place over a wide L-range and may involve inner radiation belt particles of energy up to 200 keV. It is concluded that the VLF emission generation process can occur under much more general conditions than previously believed on the basis of the results of ground-to-ground wave-injection experiments.
    Keywords: GEOPHYSICS
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  • 6
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    Particle precipitation induced by short-duration VLF waves in the magnetosphere (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present investigation has the objective to study the precipitation of energetic electrons into the ionosphere due to the interaction of these particles with short-duration VLF waves in the magnetosphere. The physics of the interaction is considered, taking into account the wave structure, the energetic particle distribution, wave-particle interaction, and the computation of the precipitated flux versus time. The obtained formulation is applied to various different magnetospheric conditions. Attention is also given to peak flux and total deposited energy. The results of the investigation demonstrate the role of the energetic particle distribution function, the normalized wave frequency, the L value of the path of propagation, the cold plasma density, and the wave intensity. The precipitated energy flux that would be observed at 1000-km altitude is presented as a function of time relative to the injection of the wave pulse at the same point.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; Aug. 1
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  • 7
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    ISEE 1 observations of VLF line radiation in the earth's magnetosphere (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: VLF line radiation in the magnetosphere is analyzed in an attempt to clarify the role of radiation from electric power lines in magnetospheric wave-particle interactions. Observations were made by the ISEE 1 satellite from October 1977 through August 1979 between L = 2 and L = 8 and 50 to 110 deg W longitude, a region encompassing the magnetic field lines linking the Eights, Siple and Roberval stations and in which VLF chorus activity had been linked to power line radiation. Line radiation was detected on 5 of 90 orbits, in all cases at frequencies below 4 kHz. The one event with a high S/N ratio exhibited lines changing frequency at rates from 22 to 6 Hz/min over a 9-min period. The radiation was detected at a time when whistler mode echoing was quite pronounced on lower L shells, and thus may have been a scattered component of line radiation echoing between hemispheres. It is concluded that very little of the background VLF wave energy in the outer magnetosphere is contained in line radiation, although the catalytic role of line radiation in controlling wave-particle interactions remains to be assessed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; May 1
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  • 8
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    Transient nonlinear pitch angle scattering of energetic electrons by coherent VLF wave packets in the magnetosphere (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Adiabatic theory is used in studying the transient nonlinear pitch angle scattering experienced by energetic electrons under the influence of coherent VLF wave packets in the magnetosphere. Finite wave packets of both fixed and variable frequency are considered, as are wide ranges of L shell, wave amplitude, and wave frequency. The results indicate that large mean pitch angle changes can be induced in the portion of the energetic population that undergoes a nonlinear cyclotron resonance interaction with the wave packet.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Oct. 1
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  • 9
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    A comparison of equatorial electron densities measured by whistlers and by a satellite radio technique (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Magnetospheric equatorial electron densities determined from whistler observations are compared with in situ satellite measurements of electron density along near-equatorial orbits. Whistler data was recorded at Siple and Palmer, Antarctica, while the sweep frequency receiver on ISEE-1 was used to measure plasma densities during passes within about 15 deg of the whistler station longitudes at L values between 3 and 5.2. The whistler and satellite data sets are found to be in good agreement for the three rendezvous considered, suggesting that the diffusive equilibrium model applied to calculate electron densities from whistler measurements was appropriate for the description of electron density distributions along field lines in the outer plasmasphere. Data also indicate that density enhancements within the whistler ducts were not more than about 30% of the mean or interduct level, and that there were no significant east-west density gradients within about 15 deg of whistler station longitudes over the L range of the study.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; Oct. 198
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  • 10
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    High altitude satellite observations of signals from the Siple transmitter (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: GEOPHYSICS
    Type: NASA-CR-173039 , NAS 1.26:173039
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