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The influence of traveling ionospheric disturbances (TID) on the caustic structure of radio waves formed during low-inclination sounding of the ionosphere has been studied. The propagation of an ordinary wave is considered. It has been established that radio waves reflected from the TID form a caustic catastrophe of type A3—a cusp. S-shaped curves formed on graphs describing the Doppler frequency shift, as well as "time loops" on graphs describing the dependence of group time on distance, were studied. Using the methods of the wave theory of catastrophes, the phase and amplitude structures of the wave field in the three-ray region were calculated. [ABSTRACT FROM AUTHOR]

Mathematical modeling of the propagation of radio waves in the decameter range between the transmitter and receiver on inclined paths during the formation of traveling ionospheric disturbances (TID) has been carried out. The features of propagation when moving TIDs in both horizontal and vertical directions were studied. The characteristics of the radio channel: the group delay time of the radio signal, the Doppler frequency shift, the dependence of the ray exit angles on the position of the TID center at various frequencies and types of polarization of electromagnetic waves are calculated. It has been established that when the inhomogeneity moves horizontally, the center of the Doppler shift curve (zero value) move depending on the type of polarization of the radiation. The shape of the Doppler shift curve changes from a sinusoidal shape to a sawtooth with increasing frequency, the group delay curve has a minimum in the region of influence of the TID, and the region of influence of the disturbance itself significantly exceeds its characteristic size. With vertical movement, a three-ray region is formed, characterized by increased values of the Doppler frequency shift and group delay times. [ABSTRACT FROM AUTHOR]

The method of bicharacteristics is used to study the propagation of decameter radio waves in the ionosphere containing the E, F1, and F2 layers and a traveling ionospheric disturbance (TID) upon slightly oblique sounding with frequency-modulated signals. The propagation of both ordinary and extraordinary waves is considered, the ionograms are compared, and their relative shift is studied. The structure of ionograms in the vicinity of caustics, which appear at the reception point at frequencies reflected in the vicinity of the E layer and TID, is studied. The divergence of the ray flux at the point of radiation reception, which determines a decrease in the amplitude, is calculated. [ABSTRACT FROM AUTHOR]

A method for reconstructing the effective frequency of electron collisions is developed on the basis of data on the attenuation and delay of frequency-modulated radio signals during the vertical sounding of the Earth ionosphere. Numerical modeling is realized in the cases of both the single-layer and double-layer models using the method of the extended bicharacteristic system. The ray trajectories of frequency-modulated decametric signals are drawn in the time—altitude coordinates. The signal absorption depending on the frequency, signal amplitude characteristics, and the frequency dependences of the maximal reflection altitude and arrival time are investigated. The dependences of the vertical component of the wave vector on the altitude and time are studied. The developed technique of experimental data processing makes it possible to obtain the dependence of the effective collision frequency on the altitude with the good accuracy. [ABSTRACT FROM AUTHOR]