MHD-Wave Generation by HF-Heating - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 362

Choosing different regimes of the amplitude modulations of the HF-pumping
wave one can generate an ULF-magnetic signal of the desire geomagnetic pul-
sation type. The first results on the producing and extraction of an artificial
ULF-signal were obtained in ([4], [10], [15], [22], [25]).

13.2 Ionospheric Heating

The basic regularities in the behavior of the non-stationary chemical kinetics
of the E -layer, numerical and analytical estimations of the intensity of ge-
omagnetic variations for various powers of the emitting system and various
regimes of the pump wave frequency, amplitude modulation, etc., are briefly
presented here. The following procedure is used: first, the distortions of the
ionospheric parameters at the axes of the nonlinear wave beam radiated from
the ground are calculated; then the perturbation of the integral conductivity
within the heated ionospheric spot is found; and, finally, the intensity of the
produced variation on the ground is estimated.
To estimate the disturbances of conductivity and, hence, the values of
anomalous currents, we use Ohm's law (1.82), (1.83). We concentrate on the
most conductive ionospheric region, i.e. E -layer. In Ohm's law, we neglect the
neutral-ion collisions in comparison with the modulation frequency ω . This
assumption is valid for the processes with scale less than 1 hour, virtually
irrespective of altitude. We also assume that the electron-neutral collision fre-
quency, ν en , to be equal to the sum of electron collision frequencies, ν ek , with
k th neutral components of the ionospheric plasma, each ν ek being dependent
on the electron temperature, T e .
A modulated HF-wave comes to the ionosphere and when it reaches heights
where electrons are magnetized, it splits into two components, the ordinary
and extraordinary waves. In the case of the longitudinal propagation along
the geomagnetic field, the ordinary wave has right-hand circular polarization
and rotates clockwise together with the electrons. The wave energy stored in
the wave is being converted into heating, mainly in the electron component
of the ionospheric plasma.
The rate of electron temperature change must satisfy the equation of en-
ergy conservation for the E -layer [14]

dT e
dt

2
3 e v e ·

= − E − δ en ν en ( T e − T n ) , (13.1)

where δ en is a portion of the energy transferred through the collision of an
electron with neutral particles, v e is the directed velocity obtained by an
electron under joint action of the electric and magnetic fields. For elastic
collisions, δ en ≈

2 m e /m n . Let the right-hand and the left-hand circularly
polarized waves are incident normally onto the ionosphere with a vertical B 0 .
Then a solution of (13.1) for the electron temperature T e with initial T e = T e 0