Abstract :
There are several groups of ionospheric data which have been analyzed during the recent decades in search for long-term trends in the upper atmosphere and ionosphere. The data on the radio wave absorption in the D region indicate to some systematic trends which may be considered as a manifestation of a temperature decrease around the mesopause. Analysis of rocket measurements of the electron concentration in the D region reveals strong enough positive trend in the upper D region. Several groups claimed positive trends of the E-layer critical frequency, foE. Also negative trends of the ratio of two principal ions in the E region ([NO+]/[O2+]) were found. These trends of three independently registered parameters may be interpreted as an indication to the existence of pronounced trends of dynamical processes at altitudes of the D and E regions. In many publications trends of the F2-layer parameters have been considered. Trends in both, the critical frequency foF2 and maximum height hmF2, were found. It was also found that the foF2 trends depend strongly on geomagnetic latitude and geomagnetic activity. This fact makes it possible to assume that the trends are not a consequence of the «greenhouseå cooling of the upper atmosphere (as has been numerously suggested) but manifest secular changes of geomagnetic activity, which influences F2-layer parameters though ionospheric storms. Trends in ionospheric storm number and intensity have also been claimed. However, even if trends of a geomagnetic origin input considerably into the observed long-term changes of foF2 and hmF2, there still may be a «nongeomagneticå component in these changes manifesting «greenhouseå (or other antropogenic) trends. The question is still open.
