Engineering topics

Katsufrakis, J. P.

Publications and source records attributed to Katsufrakis, J. P..

9 records

NASA NTRS1985

A new type of VLF emission triggered at low altitude in the subauroral region by Siple Station VLF transmitter signals

The present paper has the objective to report the existence of a new phenomenon in which coherent VLF signals from the Siple Station VLF transmitter (Antarctica, 76 deg S, 84 deg W) are observed to trigger a new type of VLF emission, taking into account the propagation of these signals upward through the ionosphere and low-altitude magnetosphere to the ISIS 2 satellite at 1400 km altitude. The existence of the impulsive emission (IE) effect lends credence to the idea that coherent VLF signals can act as catalysts to trigger natural plasma instabilities in the subauroral ionosphere and lower magnetosphere. Controlled studies of these instabilities may, therefore, be possible.

Bell, T. F.↗

NASA NTRS1985

Recent research on magnetospheric wave-particle interactions

Highlights of recent Stanford University VLF research in the Antarctic include new observations of wave-induced particle precipitation and controlled experiments on nonlinear wave growth phenomena. Higher-than-expected levels of burst precipitation have been discovered inside the plasmasphere, near L = 2, using subionospheric signal perturbations called 'Trimpi events'. Studies of burst precipitation have been extended to the region poleward of the plasmapause using the Siple transmitter signal as a waveguide probe. Experiments on the 'coherent wave instability', using the amplitude and frequency modulation capability of the new Siple transmitter, have produced exciting new results. Examples are: (1) better definition of the power threshold for the stimulation of temporal wave growth, (2) generation of strong sidebands by unamplified 'beat' waves and (3) generation of chorus-like elements within a band of simulated hiss. Using a new digital processing technique developed at Stanford, new features of the phase behavior of growing waves have been found. Opportunities for extending these experiments are discussed.

Helliwell, R. A.↗

NASA NTRS1985

Subionospheric VLF/LF phase perturbations produced by lightning-whistler induced particle precipitation

Rapid phase perturbations of subionospherically propagating VLF/LF signals are associated with lightning-generated whistlers which propagate in the magnetosphere. The perturbations, called 'Trimpi events' or 'Trimpi effects' after their discoverer, are attributed to alterations in the earth-ionosphere waveguide caused by localized enhancements in the ionospheric D region. These enhancements are produced by bursts of high-energy electrons which are precipitated out of the earth's radiation belts by the whistler waves. The present paper has the objective to present and discuss new evidence of whistler-associated phase perturbations of subionospheric signals. Events of this type, called phase Trimpi's were first reported by Lohrey and Kaiser (1979). Attention is given to occurrence statistics in terms of the seasonal distribution and hourly rate of events, possible effects on global VLF/LF navigation, and an interpretive model.

Inan, U. S.↗

NASA NTRS1984

Perturbations of subionospheric LF and MF signals due to whistler-induced electron precipitation bursts

Increasing attention is now being devoted to the problem of the pitch angle scattering and resulting precipitation of magnetospheric energetic electrons by coherent waves. The present investigation has the objective to report the first evidence of a correlation between whistlers and amplitude perturbations on low-frequency (LF) signals at 37.2 kHz and medium-frequency (MF) signals at 780 kHz. Whistler-correlated amplitude perturbations were observed on a 780-kHz MF signal propagating on an approximately 1800 km path from South America to Palmer. The observed MF perturbations were of order 50 percent in amplitude and developed much more quickly than other changes of comparable magnitude on the signal.

Carpenter, D. L.↗

NASA NTRS1983

The apparent spectral broadening of VLF transmitter signals during transionospheric propagation

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.

Bell, T. F.↗

NASA NTRS1983

EXOS-B/Siple station VLF wave-particle interaction experiments. I - General description and wave-particle correlations

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.

Kimura, I.↗

NASA NTRS1981

Jikiken /EXOS-B/ observation of Siple transmissions

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.

Kimura, I.↗

NASA NTRS1981

EXOS-B/Siple Station VLF wave-particle interaction experiment

Preliminary results of experiments made using the EXOS-B satellite to make simultaneous observations of VLF signals transmitted from Siple Station, Antarctica and interacting particles are reported. VLF measurements carried out by the EXOS-B wideband receiver upon satellite crossings of the Siple meridian at equatorial and high latitudes were able to detect the Siple signal on about 50% of the passes, and observed four instances of artificially stimulated emissions. Two of these cases exhibit triggering with a clear relation to the transmitted frequency format, while in the remaining two this relation is absent. Electron fluxes at energies from 3 eV to 9.5 keV are observed to be enhanced during the Siple stimulated emission events, with a distribution on the equatorial passes sufficient to satisfy the cyclotron interaction condition for parallel propagation of Siple signals of frequency about half the local cyclotron frequency.

Kimura, I.↗

NASA NTRS1975

VLF line radiation in the earth's magnetosphere and its association with power system radiation

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.

Helliwell, R. A.↗