Geoscience Reference
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magnetosphere or solar wind. Here, a toroidal region of relatively cold, dense
plasma, called the plasmasphere or protonosphere, exchanges plasma with the
ionosphere. In the remainder of the text after Chapter 6, we study the high-
latitude region. As previously mentioned, several experimental techniques are
described in Appendix A. Appendix B provides formulas and tables that will
help the reader describe ionospheric phenomena. Appendix B also defines vari-
ous magnetic activity indices used in the text.
1.2 Structure of the Neutral Atmosphere and the
Main Ionosphere
Owing to the pervasive influence of gravity, the atmosphere and ionosphere are to
first order horizontally stratified. Atmospheric structure can be neatly organized
by a representative temperature profile, while the ionosphere is more sensibly
organized by the number density of the plasma. Typical midlatitude profiles of
temperature and plasma density are given in Fig. 1.1. The atmospheric tempera-
ture initially decreases with altitude from the surface temperature, with a “lapse
rate” of about 7 K
km in the troposphere. At about 10 km altitude this tempera-
ture trend reverses (at the tropopause) and the stratosphere begins. This increase
is due primarily to the absorption, by ozone, of part of the ultraviolet portion
/
Neutral gas
Ionized gas
Protonosphere
Thermosphere
1000
1000
F Region
E Region
Mesosphere
100
100
D Region
Stratosphere
10
10
Troposphere
Day
Night
1
1
10
3
10
4
10
5
10
6
0
400
800
1200
1600
Plasma density (cm
23
)
Temperature (K)
Figure 1.1
Typical profiles of neutral atmospheric temperature and ionospheric plasma
density with the various layers designated.
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