Geoscience Reference
In-Depth Information
170 and 1700 MW the effective power in a source. The electron concentration
N e has been assumed to be independent of T e . Parameter γ indicates a depth
of the low-frequency amplitude modulation of the pump frequency ω. In the
shown examples, γ = 0 means that it is considered to be a monochromatic
non-modulated wave. The pump frequencies measured in MHZ are shown at
lined in the Fig. 13.1.
At heights over 85
T e 0 decreases with
frequency. This is caused by decrease of both the amplitude of the electric
field E , and the eciency of energy transfer from the pump-wave to electrons
with ω increasing. Besides, E -amplitude decreases due to decreasing radio-
wave damping in the D -layer with frequency. Starting with
T e = T e
90 km the jump of
85 km we have
ω
ν e and ν e can be omitted in the denominator at the right-side of (13.2).
Hence,
e 2
3 e
E 2
ω ce ) 2 .
Thus the jump of the electron temperature decreases in inverse proportion
to ( ω
T e =
( ω
±
ω ce ) 2 . The electron temperature is almost independent of wave fre-
quency at heights
±
85 km for E 0 = 5 V/m. At these altitudes the electron
collision frequency increases under heating by the wave of such amplitude up
to ν e
10 8 s 1
ω . Then in (13.2) in the denominator at right-side the term
ω ce ) 2 can be omitted. Hence the frequency of the pump-way does not
influence the electron temperature.
Equation (2.1) shows that increasing of the electron temperature T e in
the HF wave pump field leads to the electron-neutral collision frequencies,
ν en , rise and to change of the conductivities σ P (1.86) and σ H (1.87). We
obtain a new height profile of σ P ( z )and σ H ( z ) . The ionospheric conductivity
is perturbed up to the reflection point of the wave pump.
For the wave of small amplitude, the reflection point is located where the
frequency of the incident wave ω is equal to the plasma frequency ω pe .The
height of penetration of the non-linear wave depends not only on the sounding
frequency ω but also on the wave amplitude because the wave changes the
medium it propagates over.
Integrating σ P and σ H over height, we find Σ P and Σ H of the heated
ionosphere. Let perturbations of the background Σ P 0 and Σ H 0 before HF
wave pump heating be δΣ P 0 and δΣ H 0 ,thatis δΣ P = Σ P 1
( ω
Σ P 0 and
δΣ H = Σ H 1
Σ H 0 .
The relative variations of the Pedersen and Hall conductivities
δΣ P,H
Σ P 0 ,H 0
Σ ( P,H )0
Σ P 0 ,H 0
are shown in percents in Fig. 13.2 as functions of the frequency f for the
applied electric field E =0 . 5 V/m at the bottom of the ionosphere z =65km.
The dayside (left panel) and nightside (right panel) summer ionospheric mod-
els (IRI-2001 [29]) were taken. The calculations were performed to both the
right-hand and the left-hand polarized waves.
= Σ ( P,H )1
Search WWH ::




Custom Search