Showing papers on "Very low frequency published in 1985"

Ionospheric modification experiments with the tromso heating facility

Abstract: The experiments performed up to mid 1984 with the heating facility at Ramfjordmoen near Tromso, Norway, are summarized. These experiments comprise D -region modification, polar electrojet modulation at VLF, ELF and ULF frequencies, excitation of E -region small-scale irregularities and of F -region small- and large-scale irregularities, anomalous absorption of HF wave on long and short time scales, excitation of incoherent backscatter plasma and ion lines, stimulated radio wave emission and F -region in situ measurements.

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

Abstract: 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.

Precipitation of radiation belt electrons by man-made waves: A comparison between theory and measurement

Abstract: The temporal and spectral shape and the absolute flux level of particle pulses precipitated by a VLF transmitter are examined from a theoretical point of view. A test-particle model of the gyroresonant wave-particle interaction is applied to the parameters of the observed cases for calculating the precipitation characteristics. The temporal shapes of the precipitation pulses are found to be controlled (1) by the pitch angle dependence of the particle distribution near the edge of the loss cone and (2) by the multiple interaction of the particles with the waves due to significant atmospheric backscatter.

DE 1 observations of siple transmitter signals and associated sidebands

Abstract: Initial results from an active wave injection experiment aimed at studying coherent VLF wave propagation and wave-particle interactions in the magnetosphere are presented. The VLF signals were injected from a transmitting facility at Siple Station, Antarctica, and were received on the high-altitude, polar-orbiting Dynamics Explorer 1 satellite. Data received by the satellite are described and measurements of the propagation delay, signal amplitude, and in situ electron densities are discussed. Ray propagation paths to the satellite for two days are discussed, and sidebands associated with Siple signals observed on one of the days are presented.

A new VLF method for studying burst precipitation near the plasmapause

Abstract: VLF signals in the 2–4 kHz range transmitted from Siple Station, Antarctica (L ∼ 4.3), and received at various Antarctic locations have been used to detect the occurrence of burst precipitation of electrons (E ≥ 50 keV) into the nighttime lower ionosphere. The receiving stations, each ∼1400 km from Siple, were located to the north at Palmer (L ∼ 2.3), to the east at Halley (L ∼ 4.3), and to the south at South Pole (Λ ∼ 74°). Rapid changes in the received phase and amplitude of the Siple signal (“Trimpi events”) were observed in conjunction with the reception of one-hop whistlers. In one case involving propagation paths lying poleward of the plasmapause, amplitude decreases by ∼20% in ∼2 s, decaying in ∼7 s, were recorded simultaneously at Halley and South Pole. Post facto analysis of the South Pole records using a new digital processing scheme showed corresponding fast phase advances of ∼15 µs. In a case of phase perturbations at Palmer, the Siple signal path crossed the plasmapause projection, and the associated whistlers propagated in the outer plasmasphere. Phase measurements appear to be a particularly sensitive means of detecting burst precipitation activity under experimental conditions of the kind described. The length and spatial distribution of the signal paths provide a basis for studying the occurrence and approximate location of burst precipitation in regions outside the observing range of most instruments used for detection of precipitation. Direction finding on correlated whistler events as well as dispersion analysis may be used to increase the spatial resolution of the method.

X-Ray Microbursts and VLF Chorus

Abstract: On January 4, 1978, at 1140 UT, a SuperArcas sounding rocket was launched from Siple Station, Antarctica (L = 4.2, 76 deg S, 84 deg W), during a geomagnetically disturbed period (Kp = 6-) with intense X-ray and VLF chorus activity. The parachuted payload observed an intense microburst precipitation event of 10-minute duration. These data have been correlated with measurements of FLF chorus by receivers on the ground at both Siple and its magnetic conjugate point, Roberval, Quebec. Detailed one-to-one correspondence between the microbursts and the chorus was not a consistent feature of the data. Time series analysis fo the data did indicate a significant correlation between the Siple X-ray precipitation and the Roberval VLF waves with an arrival time delay of 0.1 + or 0.3.

A very low frequency radio astronomy observatory on the moon

Abstract: Because of terrestrial ionospheric absorption, very little is known of the radio sky beyond 10 m wavelength. An extremely simple, low cost very low frequency radio telescope is proposed, consisting of a large array of short wires laid on the lunar surface, each wire equipped with an amplifier and a digitizer, and connected to a common computer. The telescope could do simultaneous multifrequency observations of much of the visible sky with high resolution in the 10 to 100 m wavelength range, and with lower resolution in the 100 to 1000 m range. It would explore structure and spectra of galactic and extragalactic point sources, objects, and clouds, and would produce detailed quasi-three-dimensional mapping of interstellar matter within several thousand parsecs of the Sun.

Detection of local and long‐path VLF/ELF radiation from modulated ionospheric current systems

Abstract: This paper describes the local and long-path very low frequency/extremely low frequency (VLF/ELF) radiation produced by modulation of the ionospheric current systems during high frequency (HF) heating of the ionospheric D region and very high frequency (VHF) heating of the equatorial electrojet A brief description of the theory and the geometry of the heating experiment is followed by a discussion of local VLF/ELF radiation detected near the HF transmitter locations at Arecibo, Puerto Rico, and at the Jicamarca Radar Observatory near Lima, Peru Long-path detection of VLF/ELF radiation initially recorded on a path from Tromso, Norway, to the Pennsylvania State University in 1981 is updated with current experimental long-path results over paths between Jicamarca, Peru, and Salinas, Puerto Rico, as well as Arecibo, Puerto Rico, to the Pennsylvania State University

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

Abstract: 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.

Specific resistance measuring apparatus for earth's crust

Abstract: PURPOSE:To measure 3 components in the magnetic field measurement and 2 components in the electric field measurement simultaneously by switching extremely low, ultra low and very low frequency band amplification circuits with one measuring device. CONSTITUTION:Regarding a magnetic field, an induction output of a magnetic sensor 1' is obtained as cleared of a noise frequency through a differential amplification circuit 1, a notch filter 2 and an attenuation circuit 3. When this output is amplified, VLF (very low frequency), ELF (extremely low frequency) and ULF (ultra low frequency) amplification circuts 4, 5 and 6 are changed over with a selector switch 16 and outputs of the circuits 4-6 are changed over with a selector switch 16' interlocking the switch 16. Then, waveform thereof is observed via a buffer circuit 15. Outputs of the circuits 4-6 are inputted into VLF, ULF and ELF BPF7-9, outputs of which are changed over with a selector switch 16'' interlocking the switch 16 and provided to a display circuit via a rectification circuit 10, an LPF11 and a DC amplification circuit 12. In this circuitry, sensors are provided for the magnetic field in three directions, two on the plane parallel with the ground surface and one vertical thereto and for the electric field in two directions on the plane to enable a simultaneous measurement.

The distribution of a pulsed very low frequency electric field around video display terminals.

Abstract: In a video display terminal (VDT) the flyback transformer, part of the horizontal deflection and high-voltage system which sweeps the electron beam across the face of the cathode-ray tube, is a source of pulsed very low frequency (VLF) emissions. To achieve the correct beam deflection, the horizontal voltage must be pulsed at a frequency corresponding to the product of the number of lines and the refresh rate, usually of the order of 16 kHz. The pulsed positive high voltage creates the pulsed VLF field, the subject of this study. In previous studies, it was shown that the maximum intensity of the electric VLF field existed on areas of the VDT surface other than the front screen. In this study the authors compare intensities in the front, at the sides, and above the VDT.

Multispectral analysis for electromagnetic wave field components in a magnetoplasma: application to narrow-band VLF emissions

Abstract: The multispectral analysis of the wave field components of an electromagnetic wave observed at a fixed point in a magnetoplasma is performed using a maximum entropy method. The validity of the analysis is a posteriori tested comparing the propagation characteristics of the waves, as derived from the spectral matrix estimates, to the propagation characteristics predicted by the magneto-ionic theory. The techniques so developed are applied to the analysis of ground-based transmitter signals observed on GEOS 1. Comparisons with results obtained from the Welch (1967) method show the superiority of the maximum entropy method of spectral analysis, at least in the case of narrow-band electromagnetic emissions. 34 references.

The D-region winter anomaly and dynamical effects of atmospheric planetary-scale waves.

Abstract: A study is presented of the D-region winter anomaly, observed by ground based measurements of long-distance VLF radio wave propagation and HF radio wave vertical sounding at several stations located in and near Japan over 3 winters from 1974 to 1977. These winters have different meteorological conditions (i. e., a mayor stratospheric sudden warming in the winter 1976/77, a minor warming in 1974/75 and no warmings in 1975/76). The activity of the anomaly is compared with that of planetary-scale waves using atmospheric data in the lower stratosphere and radiance data in the upper stratosphere and mesosphere obtained by the PMR (Pressure Modulator Radiometer) on board Nimbus 6 satellite. The latitudinal extent and duration of the anomaly are shown to be primarily controlled by the amplification of planetary-scale wave with zonal wavenumber 1. When a major warming took place as a result of an unusual amplification of wave 1, an intense event of the anomaly was observed for a long time. However, the low-latitude boundary was high (≥40°N). The situation was similar with the case of minor warming except that the low-latitude boundary was normal (-35°N). When the wave 1 was amplified but no warmings were observed, relatively weak events of the anomaly occurred. The duration was dependent on the wave 1 activity but generally short. The low-latitude boundary became low in latitude (-30°N) with the wave 1 activity. It is further demonstrated that a localized temperature increase excited by the vertical propagation of wave 1 into the mesosphere has a close relation to the enhancement of electron density in the D-region during winter anomalous days. This suggests that the decrease of effective electron recombination coefficient due to the temperature increase is a primary cause of the winter anomaly.

An Automatic System for Global Monitoring of ELF and VLF Radio Noise Phenomena.

Abstract: : A new system has been developed for automatically monitoring and recording electromagnetic noise in the ELF and VLF (10-32,000 Hz) frequency band. Eight stations are under construction, to be installed at different sites around the world in order to map the geographic distribution of noise levels. This system is called the ELF/VLF Radiometer to emphasize the attention paid during its design and installation to making accurate absolute field strength measurements. The sensing instruments installed at each site consist of two dual-channel receivers, each with two crossed loop antennas. The ELF receiver covers the frequency range 10 to 500 Hz, and the VLF receiver the range 300 to 32,000 Hz. A bank of 16 narrowband (5% bandwidth) filters is used to monitor the energy present at selected frequencies throughout the range of both receivers. The output of these filters is continuously sampled by a computerized recording system, and statistical averages are computed on-site and recorded on digital tape, along with a sample of the raw digital data. Broadband samples of both receivers are taken periodically to provide a check on system performance and to aid in interpretation of the statistical data. Also recorded on digital tape are system status and gain information, as well as messages entered by the operator.

Recent research on magnetospheric wave-particle interactions

Abstract: 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.

Active Ionospheric Generation of ELF/VLF Waves.

Abstract: : Our work during the past year on active ELF/VLF generation has produced major breakthroughs in the understanding of nonlinear interactions in a dissipating medium such as the ionosphere for the purpose of downconverting HF to ELF/VLF waves A key result was the fact that the contrary to the conventional understanding of such processes, the presence of a dissipative medium lowers the threshold for complete decay and increases the downconversion efficiency over the one expected on the basis of the Manley rowe relations Two codes were developed and optimized (I) The first code named CMPOWER required as input a model of the ionospheric electron density and magnetic field, and the transmitter characteristics It's output is the ELF/VLF signal as a function of the modulation frequency and distance from the HF facility (II) The second named TWC (three wave coupling) is a nonlinear code, which includes dissipation and finite pump size effects (Author)

Survey of VLF-Omega transmissions received during summer in the Antarctic Peninsula

Abstract: Pres de 90 SID (Perturbations ionospheriques itinerantes) ont ete observees a partir d'enregistements d'amplitudes et de phases des signaux TBF-Omega recus a Ferraz (Antarctique)