Page 107 - Intro to Space Sciences Spacecraft Applications

Introduction to Space Sciences and Spacecraft Applications
94
magnetic field can be modeled by a (quite large) dipole magnet placed
within the earth and tilted about 11.5' from the earth's axis of rotation.
This theoretical magnet would not reside exactly at the geometric center
of the planet but would be displaced about 436 km off-center in the direc-
tion of the Pacific Ocean.

Interaction of the Solar Wind and the Geomagnetic Field. When the
solar wind encounters the Earth's magnetic field, an electromagnetic inter-
action occurs that deforms the geomagnetic field as depicted in Figure 4-9.
As the supersonic charged particles of the solar wind encounter the mag-
netic field of the earth, a shock front is formed across which the solar parti-
cles are deflected and slowed, similar to that which occurs in aerodynam-
ics. The distance to the earth of the shock front is about 14 earth radii (14
Re) at its closest in the direction of the incoming solar wind, increasing
greatly as the angle away from this direction increases.
Inward from the shock front, the particles exchange kinetic energy for
magnetic energy, which is what causes the geomagnetic field to deform.
The magnetopause represents the boundary where the magnetic forces
overcome the dynamic forces of the solar wind. This is a relatively stable
boundary requiring an increase in solar kinetic energies, such as occurs
with solar flares, to change significantly. The magnetopause is closest at

MAGNETO-
TAIL

Figure 4-9. Solar wind. The earth's magnetic field is distorted with its inter-
action with the solar wind.