Effective Conductivity of a Cloudy Ionosphere - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 293

10

Effective Conductivity of a Cloudy Ionosphere

10.1 Introduction

Up to this point, we have treated the ionosphere as a thin anisotropic layer.
As indicated in Chapter 1, to obtain the integral conductivity expression, we
use the three-fluid hydrodynamics model for electron, ion and neutral gases
and derive expressions for their specific conductivities. Due to the high con-
ductivity along the external magnetic field B 0 , the longitudinal electric field
vanishes and the transversal electric component is necessarily constant. This
allows us to simplify the detailed treatment and to use the height-integrated
conductivity Σ ( x, y ) instead of the specific conductivity σ ( x, y, z ).
This implies that distributed, isolated or random inhomogeneities can be
considered to be perturbations of Σ . Hence, small electron concentration per-
turbations and integral conductivity perturbations both produce small per-
turbations of local Pedersen and Hall currents. These currents flow through
an inhomogeneous ionosphere and as a consequence produce magnetic pertur-
bations above and below the ionosphere ([3], [4]).
Using Σ ( x, y ) instead of σ ( x, y, z ), we in fact replace a real physical ob-
ject by a thin sheet current. This invariably leads to some significant plasma
features to be lost. The lack of these features can, in general, have a drastic
impact on the current and as consequence on the value of Σ . Specific conduc-
tivity over the whole ionosphere is defined by both ions and electrons. It can
be presented as a sum of tensor electron σ e ( x, y, z ) and ion σ i ( x, y, z ) conduc-
tivities. Both of these conductivities have Pedersen σ P ( e,i ) ( x, y, z ) and Hall
σ H ( e,i ) ( x, y, z ) components, four tensor components in whole. The relative
contribution of these four components to the total σ P ( x, y, z )and σ H ( x, y, z )
is defined primarily by electron β e and ion β i magnetization parameters (see
Fig. 2.5).
Over the whole ionosphere from 80 km, β e 1 , but β i can be larger or

smaller than 1. As a result, Hall conductivity is governed mainly by electrons
while σ P is determined by either electrons or ions. In the low ionosphere