Inhomogeneous Ionosphere - Hydromagnetic Waves in the Magnetosphere and the Ionosphere - page 287

Fig. 9.7. Left panel. Ionospheric equivalent current system excited by the FMS-
wave with the E 0 ∝ sin θ . Azimuthal wavenumber is assumed to be 0. Equinox.
Right panel. Same as left panel, but for the summer in the Northern hemisphere

E ( ion )
S
E ( g )
S

1+ h

i h

≈

d g − d g .

(9.32)

Therefore the ratio

I ( ion )
I ( g )

10 − 2 10 − 2 =4 × − 3 ×

10 8 km/s, oscillations with period
T = 60 s under variation of the ground conductivity from σ g =10 6 s − 1 to
10 7 s − 1 . It follows from (9.30) and (9.32) that with T increasing the role of
the ionospheric current diminishes.
The left panel of Fig. 9.7 shows the ionospheric current distribution in-
duced by FMS-waves. Two current, oppositely directed vortices appear on the
sunlit part of the ionosphere in the Northern and Southern Hemispheres, and
close to the poles and the equator. These currents and their magnetic field
increase at the equator. The terminator effect takes place everywhere in the
ionosphere, and is especially strong at the geomagnetic equator.
The seasonal difference between the hemispheres leads to a significant
enhancement of the equator oscillations intensity near the terminator (Fig. 9.7,
right panel). The magnetic vector makes a π/ 2 turn when going from nightside
SW - NE to dayside SE - NW . A transition from summer to winter in the
Northern Hemisphere leads to the symmetrical rotation of the current density
vectors with respect to the equator, and to significant seasonal variations of
the polarization ellipse main axis. This effect should not appear under equinox
conditions.
However, owing to the finite conductivity of the Earth, the magnetic ef-
fect of the FMS-wave reflected from the Earth's surface will be much more
significant than that associated with the incident wave. Therefore, the total
magnetic field of the FMS-wave (incident + reflected) will not represent some

for the dayside ionosphere with Σ P =0 . 9 ×