The focus is on how ionospheric variability with height produces the different regions, which are the dominant features of the plasma medium under normal and extreme conditions over the European zone, during the last few Solar Cycles. Examples are given for months representing ionospheric summer, equinox, and winter conditions during low and high solar activity epochs, revealing significant solar and seasonal dependence, as well as local time dependence from one day to another during quiet geomagnetic conditions. Sudden TEC decreases during the most recent solar eclipses are reviewed.The Earth's ionosphere morphology has been studied for a very long time and defined so well that climatologically derived models have become widely available. These models represent ionospheric changes that occur repeatedly and persistently, quite often representing the background or reference conditions of the Earth's ionized upper atmosphere. Hence the most essential information is available on ionospheric variability with height producing the different regions, its variation during the day, by season, by geographic and geomagnetic locations, and in response to solar activity. Examples are given for months representing ionospheric summer (May, June, July, August), equinox (March, April and September, October), and winter (November, December, January, February), conditions during low and high solar activity epochs, revealing significant solar and seasonal dependence, as well as local time dependence from one day to another.All these are manifestations of complex interactions between neutral and ionized constituents, dependence on the geomagnetic field, and the influence of the magnetosphere above and/or the atmosphere below. However, some unexpected variations cannot be ignored and could be referred to as disturbances, perturbations, or even ionospheric noise. When influential solar-terrestrial sources are effectively invariable for a certain period of time, for instance an interval of a few days of geomagnetic quiet and/or unsettled conditions, the ionospheric plasma medium is not stable but instead highly changeable. The extent of this variability in some examples of unexpected