The atmosphere is the gaseous layer that surrounds our planet confined around the Earth by the action of the Earth's gravitational field. The atmosphere is conventionally divided following the variation of its temperature with respect to altitude. The lower atmosphere is identified with the troposphere, a region in which the temperature decreases as the height increases, the middle-upper atmosphere includes the stratosphere, where the temperature increases with altitude, the mesosphere, where the temperature decreases as the height, and the thermosphere, where the temperature increases again with increasing distance from the earth's surface. The exosphere is the outermost layer of the atmosphere and can be considered its upper limit. By upper atmosphere we mean the region starting from an altitude of about 50 km, in the mesosphere, and including the thermosphere and the exosphere. In the upper atmosphere, the gases are partially ionized and the density of free electrons is such as to influence the propagation of radio waves. For this reason this region is called the ionosphere. The study and monitoring of the ionosphere is, therefore, important not only in the purely scientific field, but also for understanding and predicting the harmful effects that it can cause to radio communications and satellite positioning systems (GPS, GLONASS, Galileo ).
The activity of researchers in this field consists in the study of the morphology and dynamics of the ionosphere and its interactions with electromagnetic waves and neutral parameters (thermosphere). Researches are mainly focused on radio propagation and ionospheric modeling on different spatio-temporal scales, from long-term variations to "ionospheric climatology" to space weather (Space Weather) for the characterization of geospatial phenomena that cause variability in the upper atmosphere. Climatology describes the trend of the ionosphere over long periods (years), while the ionospheric "weather" is aimed at characterizing the perturbations of the ionosphere induced by phenomena triggered by solar storms over short periods of time (hours/days). The data through which it is possible to monitor and study the ionosphere are those collected by the INGV observatories and ionospheric stations, by other ground-based observatories and by satellite missions.
INGV manages a network of ionospheric observatories for monitoring and studying the upper ionized atmosphere equipped with radars and receivers operating in the HF band (High Frequency, 1-20 MHz) and in the L band (1-2 GHz), which there are stations for measuring stratospheric ozone, the concentration of chemical compounds in the middle atmosphere (for example H2O and O3) and the columnar content of water vapour.
Given the harmful effects that the ionosphere can induce on technological communication and navigation systems, the monitoring and prediction of such effects are becoming crucial for the safety of operations based on technology that uses radio wave propagation. Among these applications, one of the most significant is assistance to civil aviation. In this context, INGV is a member of the European consortium which has been selected by ICAO (International Civil Aviation Organization) as one of the three global centers for the provision of a global Space Weather service for civil aviation safety. For this reason, INGV staff is engaged in the development of a national service for the Space Weather: le observations coming from the measurement stations of geomagnetic and ionospheric parameters are made available inside the monitoring and surveillance rooms in order to guarantee, on the one hand, the continuity of important historical series of data (useful for the study of long-term changes) and from 'another preparatory for the development of the national service for the Space Weather, oriented to the prediction of phenomena that take place in the circumterrestrial environment, especially for the purpose of mitigating their effect on technological systems.