MHD-Wave Generation by HF-Heating - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 373

0.05

0.5

Day, E 0 = 0.5 V/m, γ = 1

Night, E 0 = 0.5 V/m, γ = 1

0

0.05

0

0.1

q P , right
q H , right
q P , left
q H , left

q P , right
q H , right
q P , left
q H , left

0.15

0.5

0.2

0.25

1

0.3

0.35

1.5

0.4

2 4 6 8 2 4 6 8

Frequency, MHz Frequency, MHz

Fig. 13.7. q P and q H (see (13.19)) for the dayside ionosphere (left frame) and for
the nightside ionosphere (right frame) as functions of the pump frequency

assume that

ΓW 0 ,
where W 0 is the power radiated by the antenna in kW. It is seen from Fig.
13.3 that δN e is roughly proportional to T e :

E ∝

E 2

δN e /N e 0 ≈ T e ≈ ≈ ΓW 0 .

Therefore, q P ∼ Γ. Substituting the latter relation into (13.20),

we find that the magnitude of the magnetic field disturbances does not de-
pend in this case on the antenna gain. However, for a strong field, nonlin-
ear effects result in the fact that a strong dependence of the antenna gain
develops.
Figure 13.7 presents the values of q P and q H in percents for the dayside
ionosphere (left frame) and for the nightside ionosphere (right frame) as func-
tions of the pump frequency. In the calculations 0 . 5 V/m.
The maximal magnetic disturbances δb in daytime are

Γ and q H ∼

10 − 1
in nighttime for E 0 =0 . 5 V/m. The same calculations for E 0 = 5 V/m show
that δb

10 − 3

∼ and ∼

10 − 3 in nighttime. The reduction of the
magnetic effect when passing from relatively low electric field to the stronger
field is a result of strong attenuation of the nonlinear pump wave in the low
ionosphere. Going from this region, the wave comes to the E -layer with low
intensity and cannot heat this region significantly. On the other hand, the
strong effect in night ionosphere in comparison with the dayside ionosphere
is explained by the absence of a D -layer in the night ionosphere where the
wave decays appreciably.
At middle latitudes, the magnitude of the background S q variation is of
the order of 50 nT in daytime and 1 nT at night. Then the magnitudes of
the expected variations generated during the irradiation of the ionosphere
with a strong HF wave

10 − 4 ∼ in daytime and ∼

(10 − 2 10 − 3 )nT in daytime and 10 − 1 nT in ∼ 5 × − ∼