The paper is dedicated to analysis of total electron content (TEC) dynamics over the decade of 1994-2004. The analysis is made by calculation of vertical TEC disturbances index (W<sub>TEC</sub> index) for more than 20 stations in Northern Hemisphere. The calculation procedure allows us to obtain long series of the index for each station and thus to analyze long-term dynamics of the ionosphere disturbance level over the station. The results show that intensity of TEC disturbances rises with latitude and solar activity level. It is also shown that high-latitude station YELL W<sub>TEC</sub> variations have a pronounced leap in amplitudes at a middle of 1997. It is believed that during the period of 1997-98 there was some global changes in Earth's parameters (e.g. sea level, gravitation field, polar cap albedo, etc.). In the paper, we try to analyze the connection of the observed W<sub>TEC</sub> leap with such global geophysical changes and to find the probable reasons of the observed phenomena.