The Ionosphere and Atmosphere - Ultra and Extremely Low Frequency Electromagnetic Fields - page 43

Chapter 2
The Ionosphere and Atmosphere

Abstract This chapter contains some introductory materials on the formation,
structure, and composition of the ionosphere and atmosphere. The altitude depen-
dence of electrical conductivity is extremely important in the ionospheric study and
is thus discussed in this chapter. In the remainder of this chapter we use the tensor
of plasma conductivity to derive basic properties of shear Alfvén and compressional
waves in a homogeneous magnetized plasma.

Keywords Compressional/magnetosonic wave ￿ Ionosphere conductivity ￿

Magnetized plasma ￿ Shear Alfvén wave

2.1 Structure of the Ionosphere and Atmosphere

2.1.1 Formation and Composition of the Ionosphere

The Earth's ionosphere is a partly ionized and tenuous gas that surrounds the Earth.
In this region the collisions between the ionized and neutral particles cannot be
ignored since the number density of the neutral gas exceeds that of the ionospheric
plasma. The lower margin of the ionosphere corresponds to the height about 50 km
while the upper limit is the outer boundary of the magnetosphere. The ionosphere
plays an important role in the formation of the Earth's magnetosphere.
Photoionization and photodissociation by solar UV radiation, ionization by
energetic particle impact on the neutral gas along with recombination processes
occur in the ionosphere continuously. In the dayside ionosphere the main source
of the gas ionization is shortwave solar radiation with wavelength smaller than
103.8 nm. This process, which is responsible for the production of plasma, competes
with recombination at which ions and electrons combine to form neutral molecules
or atoms. The so-called dissociative recombination of the molecular ions is the most