Studies of wave disturbances in the mid-latitude mesosphere on VLF radio network data

1Fedorenko, AK, 1Kryuchkov, EI, 1Cheremnykh, OK, 1Zhuk, IT, 1Voitsekhovska, AD
1Space Research Institute of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, Kyiv, Ukraine
Space Sci. & Technol. 2019, 25 ;(1):48-61
Publication Language: Ukrainian
A wide global network of very low-frequency radio waves (VLF) transmitters and receivers provides the data for study the state of the lower ionosphere on a global scale systematically. However, the determination of the characteristics of the ionospheric plasma and the neutral atmosphere from measurements of amplitudes and phases of the VLF radio signals encounters considerable difficulties. This is due to both the complex nature of the interaction of radio waves with the medium when they are reflected from the ionosphere and the complexity of the chemical processes occurring with charged and neutral particles in the lower ionosphere. In this work, the possibility of determining the properties of acoustic-gravity waves from measurements of amplitudes of radio signals on relatively short paths (less than ~ 1500 km) was studied in terms of geometric optics.
          We have analyzed the possible physical mechanisms of the effect of the acoustic-gravity wave propagation at ionospheric altitudes on the amplitudes of the VLF radio signals. The obtained theoretical relations allow to calculate electron concentration fluctuations, the vertical displacement of the reflection height of radio signals, and to estimate the amplitudes of neutral concentration fluctuations due to the propagation of acoustic-gravity waves. Seasonal and daily fluctuations of the amplitudes of VLF radio waves on several European paths during 2013-2014 were studied. Data from transmitters at stations in Germany (DHO38), Great Britain (GQD) and Italy (ICV) with a reception point in France (A118) were used for this study. The features of amplitude fluctuations of radio signals in day and night conditions are analyzed. The approximate background level of acoustic-gravity waves at reflection heights is calculated by measuring the amplitudes of VLF radio signals. Its value turned out to be 200-400 m for fluctuations of the vertical displacement of volume and 1-2% for fluctuations of the relative concentration of neutral particles. It is shown that the background levels of AGW in the mesosphere of middle latitudes in the daytime at altitudes of ~ 70 km and at night at altitudes of ~ 90 km are close in magnitude.
Keywords: acoustic-gravity wave, ionospheric disturbance, very low-frequency radio wave
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