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500
400
300
200
p
5
0
a
z
100
p
fi
0
111111111111111111111111111
222222222222222222222222222
u
E
u
3
B
B
V
5
E
3
B/B
2
3.5
4.0
5.0
Log
10
density (cm
23
)
4.5
5.5
6.0
6.5
p
5
0
(a)
(b)
Figure 3.8
(a) Schematic equatorial plasma density profile in the evening local time
period. (b) Electrodynamics of the equatorial F region in which the density and conduc-
tivity profiles are modeled with a slab geometry, subject to a constant zonal eastward
neutral wind. Even though the plasma density does not fall off quickly with height alone,
the peak,
ν
in
and thus
σ
p
, falls off exponentially.
which yields
E
z
=−
uB
(3.7)
B
2
velocity equal
in magnitude and direction to the zonal wind speed. Furthermore, the electric
field in the reference frame of the neutral wind,
E
=
Note that the plasma inside the slab will drift with an
E
×
B
/
B
, vanishes. This
must be true because the current is independent of reference frame and we have
set the current equal to zero—that is, since
J
E
+
U
×
0,
E
must be zero.
In this simple model there is a very strong shear in the plasma flow velocity at
the two interfaces that is not shared by the driving neutral wind; that is, at the
interfaces, the plasma velocity changes abruptly from
u
to 0. This “prediction”
of a sheared plasma flow is intriguing, since such shears have been observed in
the equatorial F-region and are discussed following. However, in this model the
shear is created somewhat artificially by the slab conductivity assumption.
The insulating end plate assumption made here is most nearly valid at night
when the E-region molecular ion and electron pairs rapidly recombine with
no offsetting production by sunlight (see, for example, Rishbeth and Garriott,
1969). The dominant O
+
(atomic) ions in the F layer are much longer lived
and support the F-layer dynamo. As shown in Fig. 3.1, the maximum nighttime
J
=
σ
P
E
=
=
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