Geoscience Reference
In-Depth Information
Ionospheric physics as a discipline grew out of a desire to understand the
origin and effects of the ionized upper atmosphere on radio wave propagation.
The very discovery of the ionosphere came from radio wave observations and the
recognition that only a reflecting layer composed of electrons and positive ions
could explain the characteristics of the data. Most of the early work was aimed
at explaining the various layers and their variability with local time, latitude,
season, and so forth. The ionosonde, a remote sensing device that yields electron
density profiles up to but not above the altitude of the highest concentration of
charged particles, was the primary research tool. Such measurements revealed
a bewildering variety of ionospheric behavior ranging from quiet, reproducible
profiles to totally chaotic ones. Furthermore, a variety of periodic and aperiodic
variations were observed, with time scales ranging from the order of the solar
cycle (11 years) to just a few seconds. As time passed, the emphasis of ionospheric
research shifted fromquestions dealingwith formation and loss of plasma toward
the dynamics and plasma physics of ionospheric phenomena.
Ionospheric research has greatly benefited from the space program with the
associated development of instruments for balloons, rockets, and satellites (see
Appendix A
1
). The combination of remote ionospheric sensing and direct in
situ measurements made from spacecraft has accelerated the pace of ionospheric
research. Equally important has been the development of plasma physics as a the-
oretical framework around which to organize our understanding of ionospheric
phenomena. Likewise, the continuing development of magnetospheric and atmo-
spheric science has very much influenced our understanding of the ionosphere.
In parallel with these developments, the incoherent scatter radar technique
was devised (see Appendix A), and several large facilities were built to implement
it. The primary advantage of this method was the ability to make quantitative
measurements of numerous ionospheric parameters as a function of altitude
at heights that were inaccessible to ground-based ionosondes. Since interpre-
tation of the scattered signal requires detailed understanding of the interaction
between the electrodynamic waves and thermal fluctuations in a plasma, a work-
ing knowledge of plasma physics became necessary for understanding the diag-
nostics as well as the science.
Ionospheric science has thus evolved toward the point of view that is encom-
passed by the term
space plasma physics
. The central theme of this topic is the
treatment of ionospheric physics within this context, but many other important
issues are not discussed, including the topside ionosphere, seasonal behavior,
heat balance, and global morphology.
1.1.2 Organization and Limitations
As indicated in the previous section, our goal is to treat the electrodynamics and
plasma physics of the ionosphere in some detail. We do not, therefore, have the
1
Appendices A and B are located on the topic's companion Web site at http://www.elsevierdirect.
com/companions/9780120884254.
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