Short-period VLF emissions as solitary envelope waves in a magnetospheric plasma maser

International audienceSpace and ground-based experiments have shown evidence of natural short-period VLF emissions in which separate spectral elements are repeated with a periodicity of 2-7 s. Their basic morphological properties are found on the basis of original experimental data. In our opinion, excitation of such emissions is the result of quasi-linear relaxation effects that compensate for natural spectral dispersion. The quasi-linear relaxation of the energetic electron distribution function incrementally changes wave cyclotron instability and hence the VLF emission spectral forms. Some properties of the quasi-linear interaction of whistler waves with magnetospheric radiation belt electrons are studied. It is shown that quasi-linear relaxation can increase the cyclotron instability at the leading edge of an electromagnetic pulse. This effective saturation of absorption facilitates the division of VLF hiss-like emission into separate electromagnetic pulses without spectral modification from one pulse to the next. Some features and manifestations of this effective saturation of absorption are discussed. The results are important for a better understanding of temporal and spatial structures of VLF whistler-mode emissions and energetic electron fluxes

Dynamics of excitation of backward waves in long inhomogeneous systems

The spatio-temporal dynamics of excitation of a long backward-wave oscillator with a profiled resonant parameter is studied in detail. It is shown that the transition to multifrequency regimes of the rf generation occurs due to splitting the long oscillator into several shorter single-frequency oscillators with different eigenfrequencies. This fact can be useful, in particular, for an explanation of the dynamics of the intense cyclotron radiation, which is detected escaping from Earth in the kilometric wavelength range

Feasibility study of ionospheric perturbations triggered by monochromatic infrasonic waves emitted with a ground-based experiment

International audienceIn the framework of an active experiment preparation with a powerful ground-based monochromatic emitter, the modification of ionospheric plasma by infrasonic waves is examined. In this paper, theoretical models and numerical calculations take into account realistic altitude temperature dependence. A modulation of the electron density for an altitude equal to similar to100 km was determined under the assumption that the plasma is a small passive admixture. To study the expected ionospheric effects we intend to use data from an ionospheric sounder and from the low-altitude Demeter satellite, which can register representative electromagnetic signals scattered by artificial ionospheric inhomogeneities. The comparison between the obtained results and the expected ones is important for the analysis of possible acoustic-gravity wave contribution to the formation of an electromagnetic earthquake precursor. The calculations developed in this paper indicate that the power of an emitter of infrasonic waves with frequencies below than 20 Hz must be equal to or larger than 10 kW to be able to trigger ionospheric perturbations