The interest in studying the inhomogeneous structure of the Earth's ionosphere is based on every minute use of radio communications in everyday life and the exploration of outer space. Depending on the properties, the ionosphere is used by human civilization to establish long-distance radio communication. For the correct use of radio waves frequency range it is necessary to take into account the features of ionosphere, its spatial distribution and temporal variability. In addition, each region of the ionosphere is characterized by background ionization processes that depend on the season, day, solar activity, geographical location and geomagnetic activity. It is known that the external processes of both natural and anthropogenic origin impact on the Earth's atmosphere and ionosphere. Among them, the solar terminator (ST), solar eclipses, magnetic storms, earthquakes, tsunamis, explosions, rocket launches, powerful radio emission, and others play an important role. The main mechanism of energy and momentum transfer of such perturbations in the atmosphere is acoustic-gravity waves (AGW). AGW generated in the lower atmosphere and providing the energy transfer to the upper atmospheric layers manifest themselves at the ionospheric heights as traveling ionospheric disturbances (TIDs). TIDs lead to distortions of radio waves that impact on operation radars, radio communication and satellite navigation (deteriorating the accuracy of positioning). Studies of the generation of AGW and TIDs, features of their propagation and destruction, help to improve the prediction of plasma perturbations and take into account their effect on the functioning of different radio systems. That is why the study and monitoring of AGW and TIDs is an urgent task of radio physics and physics of the atmosphere and geospace, which is not only fundamental but also of great applied importance.
One of the most informative measuring instrument for ionospheric diagnostics is incoherent scatter (IS) radar. It is the only radar in Central Europe which is located in the observatory of the Institute of Ionosphere of the National Academy of Sciences of Ukraine and the Ministry of Education and Science of Ukraine (Kharkiv). Radar allows to obtain the data on the ionospheric conditions in the range from 100 to 1500 km. More complete information about ionosphere parameters, at altitudes below the maximum of ionization, is obtained using the traditional ionosonde technique.
The thesis aims to identify and analyze TIDs parameters caused by high-energy natural processes using data of IS radars; comprehensive analysis of TIDs parameters over different longitudinal sectors for different geophysical conditions and levels of solar activity; physical interpretation of the observed effects in the ionosphere.
The scientific novelty of the dissertation is determined by the tasks and the results obtained for the first time and is as follows.
1. For the first time the TIDs characteristics over Ukraine in the range of periods 5 - 125 min during long-term monitoring of the ionosphere from 2006 to 2018 in calm conditions were obtained using IS technique.
2. The main TIDs parameters near the characteristic geophysical periods and during the geocosmic storm on September 1 – 3, 2016 are estimated. The relationship of TIDs number with magnetic field changes at high latitudes is established.
3. For the first time, according to the IS radar of Institute of Ionosphere, the presence of large-scale TIDs was established throughout the year. This indicates the lack of a clear dependence of such structures appearance with geomagnetic activity level.
4. A comparison of background ionospheric parameters in the periods close to the vernal equinox and the summer solstice in 2016 was performed.
Information about TIDs characteristics over Eastern Europe has a big importance for extending the knowledge about the physics of processes occurring in the ionosphere and the mechanisms of interaction between different atmosphere layers. The obtained results of the parameters of medium-scale and large-scale TIDs can be used for improving the local model of the mid-latitude inhomogeneouse ionosphere, as well as allow to upgrade the global ionospheric models. Also, the obtained results will allow to more accurately predict the degree of instability of radio channels and adjust their parameters under different geophysical conditions. Finally, the obtained results are important for the development of techniques for predicting and estimating the geopositioning errors of global navigation satellite systems.
