M-I coupling scales and energy dumping

Abstract

The paper reviews three magnetosphere-ionosphere coupling scales characterizing (1) inverted-V auroral arcs, (2) so-called Alfvenic arcs, and (3) dense plasma clouds artificially injected into the magnetosphere. The three scale-breaking processes are different but follow all from the principle of perfect matching of the wave impedance of the energy and momentum carrier with the effective resistance of the energy dump. As a consequence, wave reflections from the ionosphere are absent or present only in a short initial phase and lead to quasi-stationary wave fields. In inverted-V auroral arcs the energy conversion occurs in the low magnetosphere by postacceleration of the current-carrying hot electrons. For the Alfvenic arc the energy is transferred first to dispersive Alfven waves which are then damped in the topside ionosphere by accelerating electrons along B and ions transversely to B. Barium plasma clouds break into narrow striations mapping to ionospheric scales that experience a strongly reduced Pedersen conductivity and thus achieve the perfect matching. It is also argued that the scale ΣP/K, derived from electrostatic mapping, is not suited to describe M-I coupling.