The Ionosphere and Atmosphere - Ultra and Extremely Low Frequency Electromagnetic Fields - page 44

Fig. 2.1 Typical daytime ( solid line ) and nighttime ( dotted line ) distributions of electron number
density with various layers designated. In this figure R represents the monthly median solar index.
Taken from the site http://roma2.rm.ingv.it/en/research_areas/4/ionosphere

essential type of recombination, which dominates in the main part of the ionosphere.
An example of such a reaction, where the molecule breaks apart, is given by

NO C C e ! N C O: (2.1)

The reaction rate of this process is nearly 10 3 times that of usual radiative
recombination of the atomic ions followed by the radiation of photons. For example,
the radiative reaction

O C C e ! O C ; (2.2)

becomes effective just above 1,000 km where the number density of the atomic ions
is 10 5 times that of the molecular ions. It should be noted that there are a variety of
different reactions between the molecules and particles that have different reaction
rates depending on the height, plasma composition, temperature, etc. Here we omit a
complete treatise on atomic ion chemistry and do not go into the detail of numerous
reactions.
In the first approximation the ionosphere is horizontally stratified. The iono-
spheric structure can be nearly organized by a representative altitude-dependence
of the plasma number density. Typical mid-latitude profiles of electron number
density versus altitude are shown in Fig. 2.1 . This profile is controlled by the