No abstract available

No abstract available

[en] Observation of plasma waves performed by the plasma wave receiver on board KYOKKO satellite in the frequency range from 45 kHz to 3 MHz is described. Plasma emissions have been detected mainly in two regions. In the auroral region, the auroral hiss is associated with the electron precipitation. The hiss occurrs in two frequency regions. One exists below the minimum of fsub(p)^- or fsub(g)^- where fsub(p)^- and fsub(g)^- are the plasma and cyclotron frequenceis of electrons, respectively and the other extends to above it. The hiss which extends to above the minimum of fsub(p)^- or fsub(g)^- is correlated with the inverted V electron precipitation with a peak energy of a few keV to 10 keV. In the equatorial region, a hiss has been also observed. Two different modes coexist in the hiss. One is a usual whistler mode observed in geographically limited regions. The other is a UHR wave which sometimes continues to be observed in the polar regions. (author)

[en] Classification of VLF and ELF electromagnetic radiations is considered. Classification is based on types of dynamical spectra of natural radiations. Regions of production and observations, types of waves, excitation mechanisms are given. 2 tabs

[en] Dimensions of ELF-choruses are determined within the numerical experiment frames. It is found on the basis of modern approaches to the turbulence problem that not less than three differential equations of the first order are needed for theoretical description of the ELF chorus properties. Development of the methodology presented is assumed to be promissing for elaborating methods of automated determination of radiation types and accuracy comparison of theoretical developments with experimental data

[en] Propagation characteristics of VLF hiss observed at the low latitude ground stations of Moshiri (Geomag. lat. 34.3⁰N) and Hiraiso (Geomag. Lat. 26.2⁰N) in Japan during quiet and disturbed days are discussed in the light of both the ducted and nonducted modes of propagation. The ducted propagation is studied by computing the enhancement factors at different altitudes along the field lines where the hiss is likely to be generated, whereas the nonducted propagation is studied by making use of ray tracing computations. It is shown that the storm-time hiss, generated at small wave normal angles (wave normal below the field line) can propagate to low latitude ground stations in the nonducted mode of propagation under the influence of negative latitudinal gradients of ionization, whereas the quiet-time hiss, generated at relatively large wave normal angles, can propagate in the normal nonducted mode of propagation

[en] ELF radiation trajectories with almost transverse orientation of vectors propagating from auroral range of the magnetosphere in direction of mean latitudes are calculated. Trapping inside the plasmasphere is shown to occur for waves with frequencies near low hybrid resonance

[en] The plasma wave instrument (PWI) on the Dynamics Explorer-1 has been used to measure polarization of auroral kilometric radiation (AKR) at frequencies of 50 to 400 kHz in both the northern and the southern nightside auroral regions at altitudes of 1 to 3 R_E above the AKR source regions. The AKR polarization sense is found to be the same as the right hand polarized auroral hiss found in the frequency range of 0.8 to 6.4 kHz. Consequently, these unambiguous direct polarization measurements of AKR lead to the conclusion that AKR escapes the magnetosphere in the R-X mode. Since DE-1 is close to the source region, it can be inferred that AKR is generated predominately in the R-X mode

[en] Waves named whistlers, chorus, hiss, saucers and low hybrid waves are often detected in space plasmas. These emissions are observed between the lower hybrid frequency and the electron gyrofrequency, but are given different names due to properties such as coherence, time duration and polarization. The waves are often classified as either electrostatic or electromagnetic, and are somtimes said to propagate on the resonance cone of the whistler mode. With the aid of dispersion surfaces, plots of frequency versus wavevector components, it can be shown that all these waves often correspond to one wave mode (one single surface). Sometimes the emissions called broadband electrostatic noise also propagate in this mode. Since electromagnetic theory for all angles of propagation relative to the ambient magnetic field is used, the smooth transition between so called eletrostatic and so called electromagnetic waves can be described in terms of a gradual change of the wavevector. To give an example of an instability over a wide range of wavevectors, a beam of auroral (keV) electrons is introduced. The highest temporal and spatial growth rates rates caused by such a beam can occur at the plasma frequency. However, a dispersion surface may be used to give some simple arguments showing that in an inhomogeneous plasma, the strongest emissions may occur below the plasma frequency. Furthermore, the significance of the resonance cone is discussed. (Author)

[en] VLF hiss is proposed to result from convective beam amplification of incoherent Cerenkov whistler radiation by the beam of precipitating auroral electrons. The beam amplification mechanism is investigated by using the lowest-order WKB wave kinetic equation and linear growth rates. It is shown that incoherent Cerenkov radiation cannot produce strong VLF hiss without beam amplification and that the beam amplification mechanism can account for the observed bandwidth and power fluxes of strong VLF hiss when the electron gyrofrequency is less than the electron plasma frequency. The theory is not adequate for high frequencies when the electron plasma frequency is less than the electron gyrofrequency, because nonlinear processes are important for frequencies near the plasma frequency