Modeling and experimental investigations for Modern Radio-Diagnostics of the impacts on ionosphere “from above and from below” using LOFAR and GNSS Data

Over the past 10 years, increasingly intensive studies of ionospheric plasma structures have been carried out using data from the Low-Frequency Array for radio astronomy (LOFAR) radio telescope system. Recently more and more attempts are taken to combine LOFAR ionospheric studies with other monitoring techniques such as GNSS observations. LOFAR detects scattering of high-frequency (HF) (MHz) electromagnetic waves (EMW) on the above-mentioned plasma structures. Astrophysical sources of such EMWs may be, for example, radio galaxies, supernovae remnants and pulsars. The plasma structures under investigations are excited due to impacts on the ionosphere “from below”, namely powerful natural hazards, including typhoons, volcanoes and earthquakes, and “from above”, in particular strong magnetic storms, accompanied by corresponding disturbances of auroral currents and due to flows of charged particles; as well as because of solar flares, eclipses and the terminator, as well as various plasma instabilities and nonlinearities, etc. Now we are focusing on identifying quasi-periodic and quasi-wave ionospheric disturbances in the low frequency range, including traveling ionospheric disturbances (TIDs). Results will be presented (1) based on developed models of linear and nonlinear TIDs in the presence of corresponding linear and nonlinear atmospheric gravity waves (AGWs); (2) appropriate modulation of the ionospheric plasma; (3) examples of scattering of high-frequency (HF) (MHz) electromagnetic waves (EMWs) on plasma structures, including the characteristics of the Doppler shift on moving plasma structures, taking into account birefringence in ionospheric plasma, as well as results regarding the qualitative influence on the scattering characteristics of EMWs such factors as height and horizontal dimensions of the ionospheric plasma scatterer. Algorithms are being developed to take into account the influence of plasma resonances and photochemical interactions on the characteristics of emerging ultra-low frequency (ULF) plasma structures. A database has been created that includes dynamic spectra of plasma disturbances with reference to the times of sunrise and sunset over a number of months in 2024. Observations of plasma structures were carried out at various LOFAR stations. Slant TEC maps are being developed on the basis of GNSS data. Spectral processing (using in particular Fast Fourier Transform, wavelets and transformation from dynamic spectra to Doppler shifter spectra) of the LOFAR and GNSS data is carried out with the aim of identifying quasi-periodic and quasi-wave ultra-low frequency (ULF) plasma structures with subsequent comparison “Theory-Experiment”.