Local variations of the total electron content (TEC) of the ionosphere as measured in the north caucasus mountains

The state of the Earth's ionosphere is an important factor characterizing dynamics of the solarterrestrial relations. The total electron content (TEC) of the ionosphere is one of the basic parameters for its diagnostics. It can be measured using the delays of radio signals from satellites of a GNSS on their ways to receivers. The solar influence on the ionosphere is of a global character. As for the Earth, its contribution, due to complex topography and weather conditions (for example, thunderstorms) can have local components, variable in time and space. When studying such disturbances, one should correctly exclude from the full spectrum of TEC variations the global part, i.e., we have to investigate the difference between local delays of radio signals and predicted global delays. It is possible to do this on-line with the use of satellite clocks. We describe a method of measuring the local variations of the total electron content (TEC) in the region of the Carpet air shower array of the Baksan Neutrino Observatory (43.3$^{\circ}$N, 42.7$^{\circ}$E). The standard 6-channel one-frequency satellite clock GPS170PCI is used. The period from 29.07.2019 to 06.09.2019 is analyzed to make statistical estimates of the coupling coefficients between command execution duration for getting GPS170PCI precise time and TEC variations according to global ionosphere maps. Conclusions are compared with calibration results obtained during a magnetic storm. It is shown that there are considerable variations correlating with the muon intensity measured at the ground level. A triple local TEC increase (about 15 min) is shown to occur in the 02.09.2019 event, its commencement being in coincidence with an underground electric discharge. The form of the TEC disturbance correlates with the variation of the electric current that propagates along the river near the experiment location. Cause and-effect relations of the observed phenomena are analyzed.