Terrestrial agents in the realm of space storms: Missions study oxygen ions

Observations from two recent space missions, the Active Magnetospheric Particle Tracer Explorers (AMPTE) and the Combined Release and Radiation Effects Satellite (CRRES), demonstrated that magnetospheric O + ions originating in the ionosphere are important terrestrial agents in geospace. In other words, the two missions showed that ionized oxygen escaping from the upper atmosphere, can play a critical role in electromagnetic processes in the near-Earth space. The major geospace processes are the magnetospheric substorm and the magnetic storm. The AMPTE and CRRES missions demonstrated that the abundance of terrestrial plasma (O + in particular) in the inner magnetosphere increases quickly, as a fast response of the ionosphere to enhanced geospace activity during magnetic storms and substorms [Daglis and Axford, 1996]. Furthermore, both the AMPTE mission and, especially, the CRRES mission showed that O + becomes the dominant ion species during the main phase of great magnetic storms [Daglis, 1997]. Great magnetic storms are most remarkable global-scale processes, and they are of particular interest because they often have severe impacts on technological systems. Neutral molecules in the ionosphere, the outermost part of the terrestrial atmosphere (altitudes above ∼100 km), are dissociated and ionized by penetrating solar ultraviolet and X-ray emissions. If the ionized atoms (mainly protons and singly charged oxygen and helium) will not recombine and if they acquire enough energy to overcome gravitation, they escape to the magnetosphere. During times of high geomagnetic activity, that is during magnetic storms or magnetospheric substorms, a variety of acceleration processes enhances the escape of plasma from the ionosphere. As a result, the active magnetosphere has a large, and occasionally dominant, ionospheric component, while the quiet magnetosphere is dominated by solar wind material. Magnetospheric He + ions originate both in the ionosphere and as a result of charge exchange of solar wind He ++ ions. Magnetospheric H + ions originate both in the ionosphere and in the solar wind. Contrary, the vast majority of magnetospheric O + originate in the ionosphere, and therefore are considered tracer ions of magnetosphere-ionosphere coupling and the associated ionospheric outflow. Only a negligible percentage of magnetospheric O + ions originates through charge exchange from solar wind oxygen ions with high charge states (O 6+). Consequently a large abundance of O + ions in the magnetosphere is equivalent to strong