Introduction

Planetary magnetospheres, by their very nature, provide plenty of possibilities for the development of energy conversion processes. Fundamentally a planetary magnetosphere (see e.g. Vol. I, Chapter 10) is simply the interface between two distinct regions: on the outside, the solar wind; on the inside, the ionosphere, atmosphere, and surface of the planet. The quite different motions of matter within the two regions, together with the role of the magnetic field in mediating the interaction between them, lead (almost unavoidably, it seems) to configurations of changing energy; the changes occur on a variety of time scales, ranging from quasistatic to explosive.

In keeping with the general approach adopted in this series of textbooks, this chapter aims to present energy conversion in planetary magnetospheres in general terms as part of a sub-branch of physics, namely the discipline of magnetospheric physics (which in turn is a sub-branch of heliophysics). Many of the concepts and basic results, however, originate from specific observations at and near Earth; accordingly, the chapter begins (Section 10.2) with a phenomenological overview of geophysical processes related to space storms and radiation. The physical description of energy conversion processes is then developed (Sections 10.3, 10.4, 10.5) and applied to interpret the phenomenology of energy-conversion events, both at Earth (Section 10.6) and at other planets (Section 10.7). The chapter concludes (Section 10.8) with a sketch of a possibly universal process.