The results of studying the structure of the high- and midlatitude ionosphere by the methods of satellite radio tomography (RT) are presented for different conditions of geomagnetic activity during the 23rd and 24th solar cycles. Special attention is paid to the results of RT studies obtained in different years based on the data from the Russian RT receiving chain installed along the geomagnetic meridian Svalbard–Murmansk–Moscow in the northwestern Russia and from two American RT systems in the West Coast of the United States and in Alaska. A variety of plasma structures of different shapes and intensities are observed in the RT reconstructions: ionization troughs (main ionization trough, auroral oval), multi–extrema wavelike perturbations, spots (blobs, patches), narrow plasma bands or threads elongated in the direction of the geomagnetic field, etc. Numerous examples of RT reconstructions are presented and structural features revealed by RT in the distribution of the ionospheric plasma are discussed.
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