Том 59, № 12 (2017)

We study the causes of sporadic and long-term variations in the polarization spectrum of the ultralow-frequency (ULF) magnetic background noise at midlatitudes. Data records of low-frequency horizontal magnetic components at the Novaya Zhizn midlatitude observatory of the Radiophysical Research Institute (56^°N, 45.74^°E) and the Japanese station Moshiri (44.37^°N, 142.27^°E) were used. Ionosonde data from the sites located in Russia (Vasilsursk station) and in Japan (Wakkanai station) were also analyzed. The effect of the sporadic E_s layers on the frequency spectrum of noise polarization was detected. It is shown that the appearance of quite intense sporadic Es layers with the cutoff frequencies f0E_s > 3–5 MHz can significantly alter the polarization spectrum parameters, which is due to variations in the optical depth and Q factor of the sub-ionospheric Alfvén resonator (sub-IAR) formed by the valley between the E and F regions. Numerical simulation of the polarization parameters of the background noise using the IRI-2012 model corrected by the ionosonde data confirmed that the Es layer about 5 km thick, with the cutoff frequencies f0E_s > 3–5 MHz, may lead to a sharp decrease in the boundary frequency f_b between the frequency ranges of the left- and right-hand polarized noise, or even to a complete disappearance of the sub-IAR manifestation in the polarization parameter spectrum. Numerical calculations have also revealed the impact of the altitude position of the E_s layer on the Q factor of the sub-IAR. The effect of variations in the altitude and cutoff frequency of the F-layer maximum, as well as the electron density at the altitudes of the E layer and the valley, on the features of the diurnal dynamics of the ULF noise polarization spectra is discussed.

We consider the features of generation of artificial ionospheric irregularities with transverse (to the geomagnetic field) scales l_⊥ ≈ 50–200 m in the ionosphere modified by high-power HF radio waves. It was found that there are at least two mechanisms for generation of these irregularities in the ionospheric F region. The first mechanism is related to the resonant interaction between radio waves and the ionospheric plasma, while the second one takes place even in the absence of the resonant interaction. Different polarization of the high-power radiation was used to separate the mechanisms in the measurements.

We numerically simulate the nonlinear phase of the Weibel instability of a two-component plasma with strong thermal anisotropy and comparable energies of the electron and ion fractions. Spatiotemporal dynamics of the current filaments and the magnetic field created by the electrons or ions is analyzed. It is found that the magnetic field resulting from the electron instability leads to the scattering of ions, decreasing the degree of their momentum distribution anisotropy and suppressing the development of the ion instability. It is shown that the long-term maintenance and evolution of a large-scale quasi-stationary magnetic field are due to the ion currents which are induced by the decaying magnetic field and start to dominate the electrons with time. The possibility of the considered scenario of the Weibel instability in a nonequilibrium laser-produced plasma is discussed.

We perform theoretical analysis and numerical simulation of cyclotron autoresonance masers, in which we propose using electrodynamic systems in the form of hybrid two-mirror cavities based on modified and conventional Bragg reflectors. It is shown that a stable regime of narrow-band generation with a multimegawatt power level can be achieved at a frequency of about 300 GHz in the described scheme of a generator based on a near-axis, moderately relativistic electron beam with an accelerating voltage of 500 kV and a current of 10 A, where the transverse size (diameter) of the interaction space is about 5 wavelengths and the guiding magnetic field is about 5 T.