Local perturbations of the ionosphere can now be produced using powerful radio waves directed vertically upward. These changes have short lifetimes of the order of seconds, minutes, or hours. The modified region is about 100 kilometers in diameter, centered at a height between 250 and 350 kilometers, and shaped in the form of a spheroid, prolate along the lines of the geomagnetic field.
Artificial modification of the ionosphere by such methods as chemical release, atomic bomb detonation, and small electron-beam accelerators has been used as a means for studying this region. The possibility of temporarily modifying the ionosphere by means of high-power, ground-based radio transmissions, has long been a goal of researchers, in view of its relative controllability, repeatability, and rapid reversibility. Such modification is useful for the determination of parameters of interest in aeronomy, for application to ionospheric telecommunications, and for the production and study of instability phenomena related to plasma physics.