Том 61, № 4 (2018)

Using a high-resolution numerical model, we simulate the gravity wave (GW) modes having supersonic horizontal phase velocities on the Earth’s surface and propagating to the upper atmosphere. Such GWs can be produced, for example, by low-frequency spectral components of the seismic waves propagating over the Earth’s crust surface with horizontal velocities of up to a few kilometers per second. According to the linear theory, GW modes with so high horizontal velocities should be trapped, with their amplitudes exponentially decreasing with the altitude. Numerical experiments with a nonlinear wave model showed that the initial acoustic–gravity wave pulse occurring when a non-stationary ground wave source is “switched on” can create a system of relatively slow moving mesoscale irregularities at altitudes from the Earth’s surface to the upper atmosphere. The trapped GW modes excited by a supersonic surface source may feed this system of irregularities with energy and ensure its existence within time intervals of up to tens of wave periods. The irregularities can form undulatory inclined wave fronts, similar to effective upward propagating GWs. Thus, the supersonic trapped modes excited on the Earth’s surface can create atmospheric internal GWs having subsonic horizontal phase velocities and spreading to high altitudes.

We study the possibilities of integral representation for the two-frequency mutual coherence function of the wave field in a randomly inhomogeneous ionosphere. The integral representation was obtained using the Double Weighted Fourier Transform (DWFT) method. We point out that the conditions of validity of the geometrical-optics approximation for frequency coherence are weaker than the same condition for individual samples. Examples of calculation of the frequency coherence functions for waves in the ionospheric plasma with the irregularities described by the Gaussian spectrum and Shkarofsky’s model are given. Simulation results show that diffraction effects reduce the width of the frequency coherence function. The capabilities of the methods for spatial processing of the wave field and its two-frequency mutual coherence function, which eliminate these effects through the Fresnel and DWFT inversions, are examined.

We reveal features of the radiation from symmetric constant-width slot lines on a conducting infinite half-plane in the electrodynamic H plane when their widths change and the lengths remain constant. Analysis of the theoretical and experimental results demonstrates that as the slot width increases in the range (0.5–1.5) ⋋₀ (the radiation frequency is equal to 10 GHz, the wavelength ⋋₀ = 3 cm, and the slot length is 5⋋₀), the width of the main lobe of the radiation pattern narrows in the E plane (which is predictable), whereas in the H plane it remains almost unchanged, which is confirmed by the consistent results of the mathematical simulation and experiments.

Although the spun light guides were developed in early 1980s, their quantity production has started only a few years ago. At present, the spun light guides with both strong and weak natural (unperturbed) linear birefringence are produced. The former are used for creating sensors of various physical parameters, mainly, current and magnetic field. The latter are very promising for use in fiber communication lines, since they have a considerable advantage over the conventional telecommunication light guides. In this work, we consider the influence of the polarization mode dispersion due to random inhomogeneities in the single-mode fiber light guides (SMFLGs) on propagation of ultrashort optical pulses in the fiber communication lines, which are based on the SMFLGs with very weak linear birefringence and strong regular twisting (such SMFLGs are called telecommunication spun light guides). The dependences of evolution of the envelope function of the ultrashort optical pulses and their spectra on the length of a spun light guide with very weak linear birefringence and random inhomogeneities are obtained by the numerical-simulation method. It is shown that an increase in the pulse width is proportional to the SMFLG length rather than occurs as per the diffuse law, as it is the case in the absence of torsion. It is established that the pulse widening to a certain (rather long) length with increasing length of the spun light guide occurs much slower than that in the untwisted light guides and faster for very long lengths. It is also shown that the relative intensity of radiation which is pumped from one orthogonal polarization mode to another over the depolarization length of nonmonochromatic radiation in the telecommunication spun light guides is small compared with unity, whereas an opposite situation is observed in the conventional telecommunication light guides.