ИСТИНА

The results of studying the structure of the ionosphere under different geomagnetic conditions by satellite radio tomography (RT) are presented. The techniques used include the low-orbiting (LO) RT based on radio transmissions from the Parus/Tsikada low Earth orbiters and the high-orbiting (HO) RT employing the signals from the high-orbiting global navigational satellite systems (GNSS). RT diagnosed a variety of the ionospheric structures: multi-extremum distributions of electron density with anomalous high values, steep gradients of electron density, narrow density features elongated in the direction of the geomagentic field, wavelike structures, blobs, patches, ionization troughs, ionospheric traces of particle precipitation, etc. Particular attention is placed on the results of RT reconstructions based on the data from the Russian (Moscow–Svalbard) RT system. The ways for constructing new indices of perturbation of the ionospheric plasma which take into account the specificity of the HORT and LORT data are discussed. The suggested new indices of the degree of ionospheric perturbation are compared to the geomagnetic activity indices. The research is supported by the Russian Foundation for Basic Research (projects nos. 16-05-01024 and 17-05-01250).