Showing papers on "Radio wave published in 1984"

Lightning-induced electron precipitation

Abstract: The broadband very low frequency (VLF, 0.3–30 kHz) radiation from lightning propagates in the Earth–ionosphere cavity as impulsive signals (spherics) and in the dispersive plasma regions of the ionosphere and magnetosphere it propagates as tones of descending or rising frequency (whistlers)1. VLF radio waves propagating in the magnetospheric plasma scatter energetic electrons by whistler-mode wave–particle interactions (cyclotron resonance) into the atmosphere2–6. These electrons, through collisions with the atmospheric constituents, cause localized ionization, conductivity enhancement, visual and ultraviolet light emissions, and brems-strahlung X rays. We have reported previously on the precipitation of energetic electrons from the radiation belts by the controlled injection from the ground of VLF radio waves7,8. Here we report the first satellite measurements of electron precipitation by lightning. The measured energy deposition of these conspicuous lightning-induced electron precipitation (LEP) bursts (∼ 10−3 erg cm−2) is sufficient to deplete the Earth's radiation belts and to alter subionospheric radiowave propagation (≲1 MHz). A one-to-one correlation is found between ground-based measurements of VLF spherics and whistlers at Palmer, Antarctica, and low-altitude satellite (S81-1) measurements of precipitating energetic electrons.

Saturn's ionosphere: Inferred electron densities

Abstract: During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densitis measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Simultaneous observations of ELF waves from an artificially modulated auroral electrojet in space and on the ground

Abstract: Radio waves at frequencies between 525 and 5850 Hz were observed simultaneously on the ground and in the VLF receiver of the ISIS 1 spacecraft during a flight over the Max-Planck-Institut fur Aeronomie ionospheric heater near Tromso, Norway, on December 9, 1981. The heater carrier frequency, 4.04 MHz, was amplitude modulated with a set of four frequencies: 525, 1725, 2925, and 4125 Hz. The satellite detected all these fundamental frequencies plus harmonics of the 525 Hz and 2925 Hz components, caused by the nonsinusoidal modulation of the carrier. Characteristics of the signal received along the satellite track are in approximate agreement with the results of three-dimensional ray tracing applied to a model of the ionosphere around Tromso. The time dispersion of the signals is best fitted with an ionospheric density model based on real time data with relatively low peak values. Observed signal levels have been transformed to power flux by using a plasma dipole theory and wave polarization information obtained from the three-dimensional ray solutions. Through the use of a magnetoplasma dipole theory for the induced D/E region current, the observed levels are found to correspond to radiation created by effective dipole currents between about 1.0 and 100 A. The geometrical optics theory also predicts two solutions for rays reaching a given satellite point near the polar limit of the reception zone, and a northern limit corresponding to a caustic surface. The frequencies of signal fades observed in this region are also predicted by the geometrical optics theory, but the fade depths are not. Simultaneous ground observations correspond to source region currents of about 1 A or less. Also, the ELF waves observed on the ground have different harmonic signal ratios and much smaller fluctuations than those observed on ISIS.

Frequency dependence of anomalous absorption caused by high power radio waves

Abstract: High power radio waves can modify the ionospheric electron density distribution to produce field aligned plasma irregularities which give rise to the anomalous absorption of HF radio waves. The coefficient of anomalous absorption of a vertically propagated radio wave due to scattering from field aligned irregularities has been calculated, taking into account the effects of the geomagnetic field on electron motions. These results are compared with those of other theoretical models. Furthermore, the scale lengths of field aligned irregularities produced by a high power radio wave during recent high latitude modification experiments have been determined from measurements of the anomalous absorption by means of this theory.

Direct access to plasma resonance in ionospheric radio experiments

Abstract: The concept of linear conversion of radio waves into electrostatic (ES) waves is adapted to ionospheric radio heating experiments. It is identified as access to the plasma resonance through the radio window. By means of existing heating facilities, large concentrations of electrostatic wave energy can be generated. The ES waves are confined to a restricted region in space, horizontally displaced in relation to the vertical over the heating transmitter along the magnetic meridian, the displacement being southward on the northern hemisphere. Ray-tracing studies of the location of the resonance region relative to the transmitter are presented, and the horizontal dimension is estimated.

Observations Indicating Parametric Instabilities in Internal Gravity Waves at Thermospheric Heights

Abstract: Theoretical studies predict a parametric instability of finite-amplitude internal gravity waves which hitherto has been observed only in laboratory experiments. The occurrence of this process in the atmosphere is of basic interest because finite-amplitude gravity waves, which are almost ubiquitous especially at upper atmospheric heights, would produce unstable flows even at large Richardson numbers. Maximum entropy power spectra of a strong internal gravity wave in the thermosphere, which was generated by a volcanic eruption and detected on records of the Doppler shift of high-frequency radio waves, in fact show good agreement with the spectra of synthetic Doppler records obtained from a calculated unstable gravity wave. The frequencies and wavenumbers observed in the gravity wave domain satisfy in particular the theoretically predicted resonance conditions. The observed Doppler records also show two significant lines in the acoustic domain which probably result from a nonlinear interaction with ...

Analysis of propagation characteristics of radio waves in tunnels using a surface impedance approximation

Abstract: A simple approximate method to analyze the propagation of radio waves in tunnels is proposed, based on a surface impedance assumption. This method is used, as a basic application, to determine the propagation constants of normal modes in circular tunnels bounded by a uniform lossy dielectric or bounded by two lossy dielectric layers. From the comparison of numerical results it is shown that our approximate solutions agree with the exact ones obtained from the general dielectric waveguide theory, with enough precision for practical purpose.

Simplified theory of first- and second-order scattering of HF radio waves from the sea

Abstract: A simplified, physically intuitive model of diffuse scattering of radio waves from a rough ocean surface is used to derive first- and second-order cross sections essentially in agreement with the standard expressions.

A comparison of radio wave and in situ observations of tropospheric turbulence and wind velocity

Abstract: The importance of radio wave scintillations introduced by tropospheric turbulence for both telecommunication and meteorological research is indicated. Amplitude, phase, and phase difference measurements of scintillation were performed at 30 GHz on an 8.2-km line-of-sight path. In situ measurements of temperature and humidity fluctuations and wind velocity and direction were done about midway on the propagation path. The measuring systems are described, and theory is presented to derive the refractive-index structure parameter C2n and wind velocity v from radio wave scintillations and the in situ measurements. Formulas are given to scale C2n and v with height. Finally, results of the experiments are presented and discussed.

Jovian decametric arcs - An estimate of the required wave normal angles from three-dimensional ray tracing.

Abstract: Three-dimensional ray tracing is applied to an analysis of variable radio wave normal angle effects on the associated decametric (DAM) arc structures in the Jovian magnetosphere. The analysis is bed on 1-40 MHz radio signature recorded during Voyage 1 and 2 passages. The frequencies considered are above the R-X cut-off, and several ratios of the emission frequency/source frequency. The ray tracing code is based on a cold plasma formula and integration of the Hasselgrove (1955) equations. It is assumed that the emission is in the R-X mode, the source lies at the foot of an Io flux tube, and the emission cone is hollow. Attention is focused on data for two intense, vertex-late, high curvature DAM arc. A possible source for the arcs is found to be doppler-shifted gyroemission from a beam of electrons with an energy of 10 keV. A value of 1.1 is set as the limit of the doppler shift of the DAM emissions.

Signal coupling apparatus

Abstract: A transmission line device for coupling two radio waves, such as horizontal and vertical polarized waves such as satellite transmissions, which are traveling in a particular direction along a pair of main transmission lines, selectively to a branch line without problem of mismatch, wherein the branch line is composed of a single feeder and selection of the two waves is effected simply by applying a positive or negative voltage to the feeder.

Multifrequency light curves of low-frequency variable radio sources

Abstract: Light curves for the low-frequency variable sources AO 0235 + 16, NRAO 140, PKS 1117 + 14, DA 406, CTA 102, and 3C 454.3, obtained in monthly observations at 318, 430, and 606 MHz using the 305-m telescope at Arecibo and in bimonthly observations at 880 MHz and 1.4 GHz using the 91-m Green Bank transit telescope during 1980-1983, are presented and analyzed. AO 0235 + 16 is found to have basically canonical variability which is attributed to relativistically moving evolving synchrotron components; but in the other sources, strong simultaneous variations at 318, 430, and 606 MHz are observed to be greatly diminished in amplitude at 880 MHz and 1.4 GHz, confirming the existence of the intermediate-frequency gap at about 1 GHz proposed by Spangler and Cotton (1981). The possibility that a second variability mechanism is active in these sources is explored.

The safe use of electro-explosive devices in electromagnetic fields

Abstract: Radio waves can induce currents in electrical firing circuits used for blasting in quarries, and for similar industrial purposes, and could cause premature detonation if sufficiently strong. The paper describes an experimental and theoretical study of the currents in typical circuits, and a set of maximum-current curves is presented. These curves form the basis of a set of safe field-strength curves contained in the British Standard guide to the prevention of inadvertent initiation of electro-explosive devices by radio-frequency radiation.

Radio wave receiving device

Abstract: PURPOSE:To receive a radio wave incoming from a wide elevation angle and to obtain information of elevation angle area in relation to the incoming elevation angle of radio wave by selecting one of signals inputted from a low elevation angle antenna and a high elevation angle antenna by a signal selecting circuit. CONSTITUTION:Signals received by a low elevation angle antenna 7 having a radiation pattern 5 directed to low elevation angle including nearly horizontal direction in a vertical face, and a high elevation angle antenna 8 having a radiation pattern 6 directed to high elevation angle including nearly the zenith direction and having superposed part with the pattern 5 are amplified, applied with frequency conversion and detection respectively, by receiving circuits 9-1, 9-2, and the signal intensity is measured by signal intensity measuring circuits 10-1, 10-2 and sent to a signal intensity comparator circuit 11. There, the intensity of received signals measured by circuits 10-1, 10-2 is compared, and signals higher in intensity is discriminated. A signal selecting circuit 13 selects signals higher in intensity out of signals sent from delay circuits 12-1, 12-2 according to the output of the circuit 11. Thus, receiving of a radio wave wide in elevation angle range is made possible, and the uncertainty of output signal can be eliminated by making 1 target 1 output.

Nonlinear scattering of radio waves by metallic objects

Abstract: The article contains a systematized account of experimental and theoretical aspects of the nonlinear effect of the generation of harmonics and combination frequencies at metal-oxide-metal contacts at radio frequencies. The special features and the regularities of nonlinear scattering of radio waves by metallic objects containing these types of contacts are investigated.

Transmission of electromagnetic waves in hollow tubes of metal

Abstract: Electromagnetic energy may be transmitted through the inside of hollow tubes of metal, provided the frequency is greater than a certain critical value; this value is inversely proportional to the tube radius and to the dielectric coefficient for the tube interior. Calculations and measurements of the more important characteristics of this new kind of transmission system have been made, and the conditions for minimum attenuation obtained Terminal devices for connecting a hollow pipe system to a biconductor system and others, in the form of horns, for directly radiating radio waves, have been developed; these electromagnetic horns may also be fed with ordinary coaxial lines. Certain types of terminals act as sharply resonant hollow tube elements. Several independent communication channels may be established within a single pipe line by utilizing distinct types of waves for each channel in a unique kind of multiplex operation. A section of a hollow tube may be used as a high-pass filter. Although presupposing adequate technique for the generation and utilization of the shortest radio waves, this new system possesses several features, among which are a minimum dielectric loss, substantially perfect shielding, and a simplicity of structure.

Radio communication system in radio wave shielding building

Abstract: PURPOSE:To eliminate the leakage of a radio wave to the outside of a building by constituting window glass parts of a pane where a radio wave shielding material body of the radio wave is formed as a glass surface layer or with a pane which is formed by mixing a shielding material body of a received wave. CONSTITUTION:The window glass of the window glass part B of the building A constituted by outer walls made of concrete shielding the radio wave is formed by forming the shield material body of the radio wave as the glass surface layer or forming the glass material body mixed with the shield material body. The correspondence with an external device is conducted by transmitting a signal called from each terminal device 9 through a cable or an optical fiber 7 through a central transmission/reception controller 3.

a New Radio Emission at 3 kHZ in the Outer Heliosphere

Abstract: Evidence of a radio source in the outer heliosphere based on observations made by the plasma wave receivers on Voyagers 1 and 2 at heliocentric radial distances ranging from 13 to 20 AU is given. The radio emission is observed in the frequency range 2 to 3 kHz, and is above the local electron plasma frequency whenever supporting plasma density data are available. The maximum spectral density of the emission is 10 to the minus 14 th power V sq/m/Hz. The bandwidth of the radio noise is 1 kHz. One possible source for the emission is radiation at the second harmonic of the plasma frequency at the heliopause.

Effects of a local inhomogeneity in the ionosphere on the propagation of elf radio waves

Abstract: The authors use the Stratton-Chu integral equation to solve the electrodynamic problem of the propagation of elf radio waves in the nonuniform spherical gap between the earth and the ionosphere. The authors allow for the effects of a local inhomogeneity in the ionosphere with the framework of the Born approximation of perturbation theory. The change in the perturbation of the vertical component of the electric field is analyzed as the inhomogeneity migrates along the line between source and observer and perpendicular to the propagation track. It is shown that a local inhomogeneity situated above the source or the observer can produce a substantial alteration in the level of the field compared with a uniform resonator.