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.

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The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS arrays whose elements can be selected from a large set of GPS stations forming part of the international GPS network. The method was used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The NorthAmerican sector where many GPS stations are available, and also the time interval 00:00-06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough (MIT) with a conspicuous southward wall in the range of geographic latitudes 50-60• and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 hour and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000-3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it 'curled' to the west in longitude where the local time was around noon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.

Results derived from analysing the ionosphere response to faint and bright solar flares are presented. The analysis used technology of a global detection of ionospheric effects from solar flares as developed by the authors, on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. The essence of the method is that use is made of appropriate filtering and a coherent processing of variations in the TEC which is determined from GPS data, simultaneously for the entire set of visible GPS satellites at all stations used in the analysis. This technique is useful for identifying the ionospheric response to faint solar flares (of X-ray class C) when the variation amplitude of the TEC response to separate line-on-sight to GPS satellite is comparable to the level of background fluctuations. The dependence of the TEC variation response amplitude on the flares location on the Sun is investigated.

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.