The earth's magnetosphere is composed of three major components. The first
is the solar wind, a fully ionized hydrogen and helium plasma that
originates at the sun and streams outward into the solar system at speeds of
several hundred kilometers per second. It is pervaded by a large-scale interplanetary
magnetic field (IMF), which plays an important role in the interaction
with the second essential component, the magnetosphere, a region in space
pervaded by the magnetic field. Within
about six earth radii of the earth's center,
this field is approximately a dipole field whose alignment is slightly
tilted from the earth's spin axis. At larger distances, the earth's magnetic
field is decidedly non-dipolar. It interacts with the solar wind and the
IMF in such a way as to confine the earth's field to a magnetic cavity
called the magnetosphere. Inside this cavity, a third component
is present: the earth's ionosphere. As the upper atmosphere above 80 km
is partially ionized by solar radiation an ionospheric source of plasma forms
which consists mainly of electrons, protons and singly charged helium and
atomic oxygen ions [Cow95]. It is this ionospheric plasma component of
the magnetosphere system that is
observed experimentally with the SuperDARN radars and whose properties
are analyzed in this thesis. Certain regions in the ionosphere will
be referenced frequently in the discussion that follows:
the E-region (or E-layer) located at around 100-170 km and
the F-region (or F-layer) at around 170-500 km in
height.
Each layer has a distinct maximum
in the electron density versus height profile; the heights of the maxima
are roughly 110 km for the E region and 320 km for the F region.
They are not really at fixed values but rather are indicative of
the center of regions that are very
dynamic. Figure 2.1
shows an example of the electron density profile at
latitudes where the Saskatoon SuperDARN radar makes measurements.
Figure 2.1: Electron density profile for local noon and midnight
at Rabbit Lake, Sask. as derived from the
International Reference Ionosphere (IRI) model