Some current challenges in space plasma physics

An overview of the subject of space plasma physics is attempted. This encompasses a discussion of various ground-based and satellite studies of the near-Earth space environment, with its marked temporal and spatial variations, theoretical investigations, and numerical simulations. The important distinction is drawn between passive studies of elements of the natural system, aimed at the difficult task of understanding the self-consistent evolution of some natural processes, and active investigations, which either probe or modify natural processes, in order to improve understanding of cause and effect (e.g. of energy transformations) within the system. Linear, nonlinear, and chaotic processes can occur. Attention is paid to:

1. Energetic events on the Sun,
2. Large-scale features of the interplanetary medium, both observed directly and via scintillations of distant radio stars,
3. The magnetosphere in general, and the aurora in particular,
4. Wave-particle interactions, especially cyclotron resonance phenomena, and
5. The ionosphere, particularly when heated by powerful radio waves.

The approach adopted is to place these special topics in the context of the Solar Terrestrial Energy Program (STEP) of ICSU's SCOSTEP. Finally, mention is made of some benefits to humanity of studies of space plasma physics phenomena.