Working group 3 of the Solar-Terrestrial Energy Program (STEP) will be coordinating research on “Ionosphere-Thermosphere Coupling and Response to Energy and Momentum Inputs” in 1990–1995. The research is on plasma processes leading to ionospheric structure and irregularities, the coupling of the ionosphere-thermosphere-magnetosphere system, the special electrodynamics of the equatorial ionosphere-thermosphere region, wave processes, coupling of the mesosphere to the lower thermosphere, and aeronomic models of the ionosphere.
The earliest viewpoint of the ionosphere and thermosphere was that the state of each was determined by local processes, for example, photoionization by solar extreme ultraviolet radiation, ion chemistry, and diffusion under gravity. However, it is now understood that the states of the local ionosphere and thermosphere depend, in a complex way, not only on these factors but also on distant and global processes, such as the interaction of the solar wind with the magnetosphere and the input of tidal and gravity wave energy from the lower atmosphere. The most spectacular outcome of solar wind interaction is the polar aurora and its accompanying electrojets. Their effects are not confined to the polar regions; they result in global changes in the ionosphere-thermosphere system.