V.P. Melchinov1, A.A. Pavlov2

1,2 North-Eastern Federal University (Yakutsk, Russia)

1 melchinovvp@mail.ru; 2 aisen-pavlov@outlook.com

In this paper, we consider the seasonal variations in the field level in the LW-MW bands on a short 25 km path in the zone of permafrost. Field level measurements were carried out by using a selective voltmeter at a stationary observation point in Yakutsk within 10 years. The propagation path of radio waves passes through a treeless valley of the river. Lena. The location of transmitting radio stations with frequencies of 171, 549 and 864 kHz at the same place made it possible to reveal the frequency dependence of the range of seasonal variations at a fixed distance. On treeless paths, to which the considered path belongs, seasonal variations of the field level are associated with changes in the electrical parameters of the underlying medium. In solving the problems of propagation of radio waves, the concept of the so-called surface impedance is used, which is a complex value and is determined by the total effect of electrically inhomogeneous layers of the earth in depth. Knowing the surface impedance makes to calculate the energy characteristics of radio wave propagation. The modulus and phase of the surface impedance were measured by using the signals of transmitting the radio stations in different seasons of the year.

It has been established, that the winter values of the field level in the LW band are higher than the summer ones, and in the MW band, on the contrary, the summer values of the field level are higher than the winter ones. Theoretical calculations of the modulus of the attenuation function at frequencies of 171, 549 and 864 kHz confirmed the indicated frequency dependence of seasonal variations, which is caused by changings of the electrical parameters the underlying medium because of seasonal thawing-freezing of permafrost. An analysis of long-term measurements of the field level showed that the onset of seasonal changes in recent years at all frequencies is shifted to earlier calendar dates, which leads to a decrease the winter conditions in radio wave propagation over the earth surface. In was also established that a decrease of the field level in the abnormally hot summer months at frequencies of 549 and 864 kHz. Model calculations the attenuation function give a qualitative explanation of such a phenomenon, which consists in a change in the phase of the impedance due to an increase in the conductivity of the upper layers of the earth due to their intense heating. Due to climate warming, the conductivity of the layer of frozen loose deposits increases and the phase of the surface impedance changes, which also leads to a decrease in the field level at 171 kHz. This is indicated, by the results of measurements of the field level over the last years of observations.

Accounting for seasonal variations is of practical importance for improving the efficiency of communication systems in the LW-MW bands in permafrost conditions.

Melchinov V.P., Pavlov A.A. Variations of the groundwaves field at LW-MW bands for 1998-2009 years. Radiotekhnika. 2023. V. 87. № 12. P. 78−87. DOI: https://doi.org/10.18127/j00338486-202312-09 (In Russian)

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