Radio Physics and Radio Astronomy (Jun 2019)
TO THE QUESTION OF CHOOSING THE MODEL OF WEAK INTERPLANETARY SCINTILLATIONS OF COSMIC SOURCES RADIOEMISSION IN RANGE FROM 8 TO 80 MHZ
Abstract
Purpose: An overview of the models of electromagnetic wave propagation in random media for the possibility of using them to describe the weak interplanetary scintillations of radio emission of cosmic sources in the range from 8 to80 MHz, as well as estimation of the applicability conditions of the models for this case and comparison of the scintillation spectra calculated on the basis of different models. Design/methodology/approach: literature review, analysis, mathematical calculations. Findings: On the basis of scientific publications, the problem of propagation of radio emission of cosmic sources with frequency in the range from 8 to 80 MHz in the interplanetary plasma in the weak scattering regime (large elongations) is considered. The stages of solving the problem are shown, when by taking into account some certain constraints a gradual transition from the Maxwell equations to the simpler parabolic equation is carried out. The main approximate methods of solving the parabolic equation (the Rytov method, path integral technique, the phase screen model) are considered. An estimation of the conditions for the applicability of the parabolic equation itself and the above-mentioned methods for finding approximate solutions is made. The evaluation showed that both the parabolic equation and the above-mentioned methods for finding its approximate solutions can be used in the case of the problem of propagation of radio emission of cosmic sources with frequency in the range from 8 to 80 MHz in the interplanetary plasma in the weak scattering regime. For each method, expression for the scintillation spectrum taken from literary sources is given. By calculation it is shown that in the weak scattering regime, the Rytov method, path integral technique and the phase screen model give close scintillation spectra. A small change in the parameters of the interplanetary plasma can fit each model spectrum with the experimental one, but such variations of the model spectrum will be of the order of the error of obtaining the experimental spectrum, which, in the normal statistics of interplanetary scintillation observations in the range from 8 to 80 MHz, is 10 to 20 %. Conclusions: Three methods: the Rytov method, path integral technique, the phase screen method (with caution) can be applied to simulate the weak interplanetary scintillations of cosmic sources radio emission in the range from 8 to 80 MHz.
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