Introductory and Background Material - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 24

Interplanetary
medium

Magnetosheath
Magnetopause

Bow
shock

Tail
boundary
layer

Cusp

Northern
tail lobe

Dayside
boundary layer
(entry layer)

Field-aligned
currents

Geomagnetic
field lines

Magnetotail

Auroral
precipitation

Ring current

Plasma sheet

Solar
wind
plasma

Radiation
belt region

Radiation
belt region

Plasmasphere

Neutral
sheet

Southern
tail lobe

Auroral oval

Bow
shock

Magnetosheath

Figure 1.17 Schematic representation of the magnetosphere. (Courtesy of J. Roederer.)

field lines that convect back to the earth. As the hot plasma sheet flows toward
the earth into an increasing magnetic field, the differential motion of the ions
and electrons produces a ring current somewhat analogous to the interaction
between the solar wind and the magnetosphere itself on the sunward side of
the earth. Some of these hot plasma sheet particles move along the magnetic
field lines and precipitate into the atmosphere in a ring around the polar regions
called the auroral oval. This ring forms the light pattern seen in Fig. 1.6. Most
of the solar wind and magnetospheric effects occur at high latitudes, although
many interesting phenomena do extend to lower latitudes during active times.
The active region is skewed in the antisunward direction, extending to 70 ◦ mag-
netic latitude on the sunward side and 60 ◦ on the nightside. In this text, some
of the phenomena indicated in Fig. 1.17 will be treated in detail and others in a
more sketchy fashion. The interested reader is referred to the text by Lyons and
Williams (1984) and Kivelson and Russell (1995) for more complete treatises on
magnetospheric processes.
Particle energization processes will not be discussed quantitatively at all in
this text, but a brief sketch is in order here. Solar wind electrons have thermal
and flow energies of only a few electron volts, while the bulk flow energy of
the ions is about a kilovolt. The earth's bow shock wave, shown in Fig. 1.17,
energizes the electrons to many tens or even hundreds of electron volts in the
magnetosheath. Some of these hot electrons and ions directly penetrate into the
ionosphere in the connection process or through the cusp in the magnetic field
geometry. This precipitation of energetic particles contributes to the dayside part