Using long-term data from Yakut meridional chain of Yakutsk — Zhigansk — Batagay — Tixie ionospheric stations, we study ionospheric signatures of fast subauroral ion drift. Sharp drops or “falls” of critical frequencies (FCF) of the ionospheric F layer are shown to be one of the main signatures of the development of fast subauroral ion drifts near or at the zenith of the observation station. Comparison between long-term ground-based and satellite measurements indicates that there is good agreement between seasonal variation in the probability of occurrence of FCF derived from ground-based data and subauroral ion drifts derived from DMSP satellite data. Such a coincidence implies that both satellite and ground-based measurement methods register the same phenomenon in the boundary layers of the plasmasphere, namely, the appearance and development of electric fields of magnetospheric origin. The local time for recording of falls of the critical frequency derived from the ground-based data is shown to closely coincide with the appearance time of subauroral polarization streams of plasma according to satellite data. We can therefore conclude that most of the observed FCFs derived from ground-based data refer to intense storms.