Scatter of hmF2 values as an indicator of trends in thermospheric dynamics

Analysis of the variability of the @F2-layer height, @hmF2@, from the 1950s to 1960s to the 1990s is performed on the basis of vertical sounding data for a series of midlatitude ionospheric stations. It is found that the scatter of the @hmF2@ values (standard deviation) increases sharply from the earlier decades to the later ones. This increase is better pronounced in the spring period of the year and does not depend on geomagnetic activity. The increase in the scatter of @hmF2@ indicates, evidently, the presence of systematic changes (trends) in thermospheric dynamics, the existence of these trends having been suggested in the recent publications of the author on the basis of the analysis of the foF2(night)/foF2(day) and R(foF2) parameters.