Geoscience Reference
In-Depth Information
Fig. 9.6. Twin-vortex ionospheric equivalent current system arising due to the
source at the noon meridian. Equinox (left panel). In right panel are shown corre-
sponding system for the source shifted to the sunrise hours. Summer in the Northern
hemisphere
spatial distribution depends on the terminator location. However during non-
equinox conditions, due to conductivity differences between the hemispheres,
currents flow between them. This is not true during an equinox when as it
is well know, the hemisphere's conductivities are equal. In the sunrise/sunset
hours, an appreciable azimuthal component of the magnetic field, as well
as an anomaly of the main polarization axis, should appear. If the source
field-aligned current system is shifted from the noon meridian, let say, to the
morning hours (Fig. 9.6, summer in the Northern Hemisphere), the equator
disturbance intensity can reach 25 % of its value near the source.
FMS-Wave
Let us consider currents in the inhomogeneous ionosphere associated with the
FMS-wave incident on the equator. Longitudinal electric current in the FMS-
wave is nil, therefore the electric and magnetic components in such wave can be
expressed in terms of the potential ψ (see Chapter 7). If we adopt an
-
coordinate system where the local orientation of the axis are southward, east
and upward along the Earth's radius, then the horizontal electric E ( i )
{
x, y, z
}
and
y
magnetic b ( i )
components can be written in the form:
b ( i x = ψ ( i ) ω 2
x
k y sin θ
k x
c 2 A
and the electric component as
ω 2
c 2 A
ψ ( i ) ω
c
E ( i )
y
k y cos θ .
k x
 
Search WWH ::




Custom Search