The article is a review of studies of ionospheric effects carried out in ISTP SB RAS. The main results of GPS/GLONASS radio sounding of ionospheric disturbances of natural and anthropogenic origin are presented. The article is devoted to ionospheric effects of solar eclipses, solar flares, solar terminator, earthquakes, tropical cyclones, large-scale ionospheric disturbances of auroral origin, rocket launches. Dynamics of global electron content analysis is also presented. The special attention is paid on the influence of solar flares and ionospheric irregularities on GPS and GLONASS performance. The work is a tribute to the leader of GNSS-monitoring workgroup Prof.

We have obtained first experimental evidence in favour of the magnetohydrodynamic (MHD) nature of night‐time medium‐scale travelling ionospheric disturbances (MSTIDs). We used total electron content (TEC) measurement data from the dense GPS networks in California and in Japan for 2008–2009. It was found that the spectral MSTID characteristics are determined by the solar terminator (ST) dynamics. In summer, MSTIDs are detected 1.5–3 hours before the evening ST at 100 km above the point of observations, but at the moment of the evening ST passage through the magnetoconjugate point. At the equinox MSTIDs are registered at once after ST appearance. In winter, MSTIDs are observed 1.5–3 hours after the evening ST occurrence at the point of observations, but at the moment of the evening ST passage in the magnetoconjugate point. The MSTID occurring synchronously with the ST passage through the magnetoconjugate area suggest that the ST‐excited MSTIDs are of MHD nature.

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The ionospheric weather is affected not only from above by the Sun but also from below by processes in the lower-lying atmospheric layers. One of the most pronounced atmospheric phenomena is the sudden stratospheric warming (SSW). Three major SSW events from the periods of very low solar activity during January 2009, February 2018, and December 2018/January 2019 were studied to evaluate this effect of the neutral atmosphere on the thermosphere and the ionosphere. The main question is to what extent the ionosphere responds to the SSW events with focus on middle latitudes over Europe. The source of the ionospheric data was ground-based measurements by Digisondes, and the total electron content (TEC). In all three events, the ionospheric response was demonstrated as an increase in electron density around the peak height of the F2 region, in TEC, and presence of wave activity. We presume that neutral atmosphere forcing and geomagnetic activity contributed differently in individual events. The ionospheric response during SSW 2009 was predominantly influenced by the neutral lower atmosphere. The ionospheric changes observed during 2018 and 2018/2019 SSWs are a combination of both geomagnetic and SSW forcing. The ionospheric response to geomagnetic forcing was noticeably lower during time intervals outside of SSWs.