We have carried out a statistical analysis of a huge array of archival experimental data on the dynamic regime of the ionosphere over Irkutsk, obtained by a radiophysical spaced-receiver method with a small base of a radio signal reflected from the ionosphere during vertical ground-based radio sounding near Irkutsk in 1958–1982. Statistical long-term characteristics of drifts of ionization irregularities over the region of the south of Eastern Siberia were obtained. We confirmed clear differences in the nature of the dynamic regime of the lower and upper ionosphere. The motion of ionization in the zonal direction is shown to be more regular than the meridional drift. We determined the characteristic seasonal features of variations in magnitudes and directions of horizontal drift motions at heights of E and F ionospheric regions. The lower ionosphere is characterized by high variability and seasonal variations in motion velocities. In winter, the zonal component of the horizontal ionization drift velocity is directed to the west; in summer, to the east. At the heights of the upper ionosphere, the dynamic regime is more regular. The prevailing zonal direction of the motion of ionization irregularities to the west is observed for all seasons (heights above 230 km). The meridional component of the horizontal drift velocity mainly has a southerly direction. Thus, the horizontal drift of plasma irregularities at the heights of the upper ionosphere is, on the whole, directed to the southwest with the zonal direction predominating.