The ionosphere as a screen for magnetospheric processes

The ionosphere acts like a television screen by lighting up with animated displays of aurora, which result from the bombardment of particles from the magnetosphere. The particles travel along magnetic‐field lines, and important information about remote magnetospheric processes is revealed by the ionospheric emissions they stimulate. More than this, the remote processes involve structured electric fields and currents, which are also conveyed along magnetic‐field lines to the ionosphere. Consequently, ionospheric observations offer the exciting opportunity to monitor magnetospheric processes in two dimensions and to thus provide an increasingly important complement to in‐situ magnetospheric observations. This type of remote sensing helps to overcome the current sparsity of satellite missions to the magnetosphere. It is also relatively low‐cost and has the potential for global coverage and high temporal and spatial resolution. Such observations are indeed becoming increasingly valuable for the study of processes occurring in the Earth's magnetosphere. The NSF Geospace Environment Modeling (GEM) program, for example, is incorporating ionospheric observations as an integral part of its program to study magnetospheric processes.