The intrinsic magnetic field of the Earth acts as an obstacle to the solar wind and shields a volume of space, called the magnetosphere, from direct access of the solar wind. In Chapter 7, we considered the role of the magnetosphere as an obstacle to the solar wind and were mainly concerned with the region “external” to the magnetopause. The details of the internal dynamics of the magnetosphere do not seriously affect, at least to about the 95% level, the external solar wind plasma flow, but the solar wind does strongly affect the internal dynamics of the magnetosphere and ionosphere, as we will see in this chapter. This chapter will strongly emphasize macroscopic or fluid aspects of magnetospheric physics rather than the microscopic physics operating in the magnetosphere. Some aspects of the inner magnetosphere (i.e., the ring current and radiation belts) were already considered in Chapter 3.

The terrestrial magnetosphere has been extensively studied over the past 35 years with dozens of Earth orbiting satellites. The International Sun Earth Explorer (ISEE), Dynamics Explorer (DE), and AMPTE missions have been especially important, and in the near future we can expect useful information from recently launched spacecraft such as Geotail and Polar. The volume of observational and theoretical literature that exists, mainly in the Journal of Geophysics Research–Space Physics, has become immense. Much has been learned about how the magnetosphere works, although many key processes remain poorly understood.