Showing papers on "Very low frequency published in 1983"
TL;DR: The SEEP (Stimulated Emission of Energetic Particles) experiment conducted during May-December 1982 as discussed by the authors showed that approximately 15 to 50 percent of the enhanced electron flux was concentrated near the resonant energies for first order cyclotron interactions occurring close to the magnetic equator with the nearly monochromatic waves emitted from the transmitter.
Abstract: Radiation belt electrons precipitated by controlled injection of VLF signals from a ground based transmitter have been directly observed for the first time. These observations were part of the SEEP (Stimulated Emission of Energetic Particles) experiment conducted during May-December 1982. Key elements of SEEP were the controlled modulation of VLF transmitters and a sensitive low altitude satellite payload to detect the precipitation. An outstanding example of time-correlated wave and particle data occurred from 8680 to 8740 seconds. U. T. on 17 August 1982 when the satellite passed near the VLF transmitter at Cutler, Maine (NAA) as it was being modulated with a repeated ON (3--s)/OFF (2--s) pattern. During each of twelve consecutive pulses from the transmitter the electron counting rate increased significantly after start of the ON period and reached a maximum about 2 seconds later. The measured energy spectra revealed that approximately 15 to 50 percent of the enhanced electron flux was concentrated near the resonant energies for first order cyclotron interactions occurring close to the magnetic equator with the nearly monochromatic waves emitted from the transmitter.
108 citations
TL;DR: The first direct observations of the precipitation of radiation belt electrons by the controlled injection of VLF signals from a ground-based transmitter were reported from data acquired in the SEEP (Stimulated Emission of Energetic Particles) experiment.
Abstract: The first direct observations of the precipitation of radiation belt electrons by the controlled injection of VLF signals from a ground based transmitter were recently reported from data acquired in the SEEP (Stimulated Emission of Energetic Particles) experiment. That outstanding example of time-correlated wave and electron data has now been enhanced by the finding of four additional modulated events out of 65 satellite passes when one of the U. S. Navy VLF transmitters at Cutler, Maine (NAA) or at Annapolis, Maryland (NSS) was being modulated in a 3s ON/2s OFF format. During each of these events the fluxes of precipitating electrons were observed repeatedly to display a characteristic time behavior with respect to the transmitter modulation: a relatively slow rate of increase after start of the ON period leading to a maximum about 2 seconds later. Details of this consistent pattern and the statistics of occurrence of modulation events are presented along with comparisons of the absolute fluxes of precipitating electrons observed during normal transmitter operation with those recorded when one of the transmitters was modulated.
45 citations
TL;DR: In this article, the authors compare the VLF signals from modulated ionospheric heating experiments with the electric field pulsations observed by the STARE auroral radars, and show that the correlation between the VlF signals and electric field signals can provide a sensitive, high-time resolution indicator of the ionosphere electric field.
Abstract: Very low-frequency radio waves can be generated in the lower ionosphere by periodically modulating the conductivity, and thus natural currents, using high power HF radio waves. In conjunction with the heating facility near Tromso, Norway, such waves have been generated and detected on the ground using two orthogonal receiving antennas so that the polarization ellipse of the VLF signal could be reconstructed. Changes in the strength and direction of the electric field driving the modulated current are reflected in variations in the size and orientation of the VLF ellipse. During a natural Pc 5 pulsation event on October 16, 1981, a close correlation was found between the VLF signal and the electric field pulsations observed by the STARE auroral radars. This first comparison between the Heating and STARE experiments shows that VLF signals from modulated ionospheric heating experiments can provide a sensitive, high time resolution indicator of the ionospheric electric field.
33 citations
TL;DR: In this paper, the effect of ionospheric conductivity modulation at ELF and VLF frequency bands was investigated at a heating facility which generates CW power of up to 1.5 MW in the 2.5-8 MHz frequency range.
Abstract: Ionospheric modification experiments have been performed in 1980-1982 at a heating facility which generates CW power of up to 1.5 MW in the 2.5-8 MHz frequency range. D region modification experiments were performed with a partial reflection experiment facility. Amplitude-modulated heating of the D region with ELF and VLF modulation frequencies gives rise to electron temperature modulation, and therefore no ionospheric conductivity modulation. At ULF frequencies, the effect of electron density modulation dominates over the effect of electron temperature modulation. Attention is also given to HF backscatter from F region striations, the anomalous absorption of HF waves, phase changes of a diagnostic HF wave, the plasma line associated with the parametric decay instability, airglow modification, and F region cross-modulation. 19 references.
30 citations
TL;DR: In this article, the long-wave reflection properties of the high-latitude ionosphere, observed under both quiet and highly disturbed conditions, were described using a short-pulse VLF ionosounder located within the polar cap in northern Greenland.
Abstract: This paper describes long-wave reflection properties of the high-latitude ionosphere, observed under both quiet and highly disturbed conditions. The data were obtained using a short-pulse VLF ionosounder located within the polar cap, in northern Greenland. Under quiet ionospheric conditions, substantial diurnal, day-to-day, seasonal, and solar cycle variations were observed. During polar cap absorption events the VLF reflection properties of the disturbed ionosphere depended greatly on the solar illumination conditions, as well as the magnitude of the incoming energetic particle flux. The use of the steep-incidence VLF reflection data to develop and validate models of the lower ionosphere is discussed; and electron density profiles are given, derived from reflection data obtained during quiet and disturbed conditions.
17 citations
TL;DR: In this article, a large geometric factor electron spectrometer was used on the S3-2 satellite to detect spikes of electrons with energies between 36 and 317 keV in the region 1.9 L 1.6.
Abstract: : Precipitation spikes of electrons, in which the energy spread of the peak is narrow (less than 50 keV) and the peak energy is a strong function of the location in L, have been observed in the region 1.5 L 2.0 and have been ascribed to interactions between waves from high power VLF transmitters on the ground and the precipitated electrons. Instrumentation on the S3-2 satellite (polar orbit, 240 km and 1557 km perigee and apogee) included a large geometric factor electron spectrometer which, due to the characteristics of the instrument and orbit, routinely observed these precipitation spikes. Additionally, on numerous occasions when these spikes were observed at low altitude, a significant depletion of electrons at the same energies was observed high on the field line. These depletions indicate that the loss rate of electrons due to VLF transmitters is significant and usually exceeds the rate at which radial diffusion is refilling those field lines. Electrons with energies between 36 and 317 keV in the region 1.9 L 1.6 were observed to have lifetimes limited to a few days by interactions with waves from VLF transmitters. Thus the outer edge of the inner zone is defined by this wave-particle process. (Author)
17 citations
TL;DR: The direct correlations obtained between the very low frequency signals and the x-rays demonstrate the limits of sensitivity required and indicate that this remote sensing technique would be useful for future study ofvery low frequency effects induced by single lightning strokes.
Abstract: Magnetospheric electrons precipitated by ground-based coded very low frequency radio transmissions have been detected by rocket measurement of bremsstrahlung x-rays, caused by impact of the electrons with the upper atmosphere. The direct correlations obtained between the very low frequency signals and the x-rays demonstrate the limits of sensitivity required and indicate that this remote sensing technique would be useful for future study of very low frequency effects induced by single lightning strokes.
12 citations
01 Dec 1983
TL;DR: In this article, the feasibility of producing ELF signals in the earth ionospheric waveguide, by downconverting H.F. pump power in the ionosphere plasma has been investigated.
Abstract: : The feasibility for producing ELF signals in the earth ionospheric waveguide, by downconverting H.F. pump power in the ionospheric plasma has been investigated. We have found that: (i) Interaction regions of horizontal width approx. 100km, localized inside an ionospheric density gradient, can deplete the pump for pump powers above a threshold value. Minimum threshold is achieved for pumps propagating almost perpendicular to the density gradient (very oblique incidence) at 100 km altitude. The threshold power required is between 3-10 MW of H.F. (ii) The conversion efficiency from H.F. to ELF in the ionosphere could reach values of the order of 0.01. (iii) The scheme can operate either as an ELF generator if we use an H.F. pump with power 3-10 MW and a lower H.F. sideband with power 100 kw, or as an amplifier of ELF signals from weak ground transmitters (such as the Wisconsin test facility), or from weak space or balloon based antennas. A variation of the scheme can operate as a broadband ELF generator for jamming purposes. (Author)
11 citations
TL;DR: In this article, the amplitude and polarization properties of the Siple signals were predicted using a ray optics analysis, and an approximately 90° anomaly in the apparent arrival bearing of the signals from Siple was attributed to the essentially horizontal polarization of the received signal.
10 citations
TL;DR: In this paper, the NLK Jim Creek transmitter in Alaska on 18.60 and 18.65 kHz has been observed on GEOS-1 for one pass over Alaska on June 11, 1977, and the peak amplitude of the signals is ∼5 pT (0.6 mV/m), which is received when the satellite is close to exact conjugacy at 7500 km altitude.
Abstract: Signals launched by the NLK Jim Creek transmitter in Alaska on 18.60 and 18.65 kHz have been observed on GEOS-1. Data for one pass over Alaska on June 11, 1977, are presented here. The peak amplitude of the signals is ∼5 pT (0.6 mV/m), which is received when the satellite is close to exact conjugacy at 7500 km altitude. While the weaker signals received at some distance from conjugacy behave as expected from linear theory, the stronger signals received closer to conjugacy have features which indicate that some non-linear process is active. These features are: 1) a turbulent electric frequency spectrum 2) an increased electrostatic character of the waves. The threshold field amplitude of the supposed (but unidentified) non-linear interaction is ∼1 pT.
5 citations
Patent•
16 Mar 1983
TL;DR: In this paper, an underground structure was analyzed two-dimensionalally, by providing a device, which receives a very low frequency band and an ultra-low frequency band, and a noise eliminating filter which eliminates the noise due to a commercial power source and comparing an apparent specific resistance value with a model calculation result value.
Abstract: PURPOSE:To analyze an underground structure two-dimensionally, by providing a device, which receives a very low frequency band and an ultra low frequency band, and a noise eliminating filter which eliminates the noise due to a commercial power source and comparing an apparent specific resistance value with a model calculation result value. CONSTITUTION:Very low frequency electromagnetic waves, which are propagated by the Schumann resonance phenomenon or the like and exist naturally, and ultra low frequency electromagnetic waves transmitted from an omega station are used, and the magnetic field is measured by an inductance coil 11, and the electric field is measured by electrodes 12 and 12. The coil 11 has about 50,000 turns, and electrodes 12 and 12 are about several tens meters apart from each other. A band eliminating filter 2 is installed for the purpose of eliminating the noise due to the commercial frequency. An apparent specific resistance value for every frequency is obtained on a basis of measured numeric values and is compared with the calculation result value of a layered structure model by a preliminarily programmed computer, and next, the specific resistance is changed in the depth direction and the horizontal direction, and the underground structure is analyzed two-dimensionally similarly.
TL;DR: In this article, it was shown that wave-particle interactions involving both broadband incoherent ELF waves and narrow band coherent very low frequency (VLF) waves may not produce a sufficiently high rate of pitch-angle scattering.
Abstract: Recent satellite observations1 have revealed details on the strength of the pulsing extremely low frequency (ELF) hiss in the equatorial region which maps down to the auroral zone. It is shown here to be insufficient to produce pitch–angle scattering of energetic electrons into the loss cone at a sufficiently high rate to explain the characteristics of the measured pitch-angle distributions in pulsating auroras, within the framework of the theory proposed by Coroniti and Kennel2. It is suggested that wave–particle interactions involving both broadband incoherent ELF waves and narrow band coherent very low frequency (VLF) waves may be able to produce a sufficiently high rate of pitch-angle scattering.
TL;DR: The results of the Intercosmos-19 satellite experiment which receives VLF signals arriving via a magnetospheric path have been examined in this paper, showing that the reception zone in the magnetically conjugate region (MCR) has been shown to be centred near the L -value (2.6) of the transmitter of 15 kHZ radio waves.
Journal Article•
TL;DR: The very low frequency electromagnetic prospecting equipment measured different space and phase components of the electromagnetic field in the frequency range 15-25 kHz emanating from distant naval radio stations as discussed by the authors, which demonstrated the usefulness of the investigations in groundwater and geological mapping.
Abstract: The very low frequency electromagnetic prospecting equipment measures different space and phase components of the electromagnetic field in the frequency range 15–25 kHz emanating from distant naval radio stations. The field application of the equipment designed and constructed for this purpose has demonstrated the usefulness of the investigations in groundwater and geological mapping. The amplitude measurements necessitate correction of the diurnal variations of the electromagnetic field at the observation point.