Electrodynamic Properties of Space - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 27

N i (cm-3)
Fig. 2.1. Left frame: the equatorial distributions of the ion concentration N i (solid
line) and Alfven velocity c A (dashed line) as functions of the dimensionless radial
distance L = r/R E . Curves marked by ' a ' respect to the disturbed conditions, and
by ' b ' is quiet conditions. Right frame: as the left frame for the transversal and
longitudinal components of the dielectric permeability
The Alfven Velocity
It follows from (1.95) that the Alfven velocity c A is determined by the cold
plasma density and the magnitude of the magnetic field. The left frame
of Fig. 2.1 shows the distributions of cold plasma and c A in the equa-
torial plane of the magnetosphere versus the radial distance L = r/R E .
Line 2 a refers to c A ( L ) for a disturbed and 2 b for a quiet magnetosphere.
Corresponding distributions of cold plasma densities are lines 1 a and 1 b ,
respectively.
The transversal dielectric permeability of the magnetosphere is ε m = c 2 /c 2 A
(see (1.103)). Since the longitudinal dielectric permeability ε is greater than
ε m because of the rarity of electron and ion collisions, in the first approxima-
tion ε can be set to infinity. Hence the magnetosphere in the ULF range is a
strongly anisotropic dielectric with finite permeability ε m across the magnetic
field and infinite ε along it.
2.2 Ionosphere
High frequency radio soundings discovered the stratified structure of the
ionosphere and detected layers with different electron concentrations [11].