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10
2
5
cm
2
3
10
2
5
cm
2
3
1500 sec
N
0
1850 sec
N
0
3
3
0.0
676
0.5
1.0
1.5
2.0
2.5
0.0
676
0.5
1.0
1.5
2.0
2.5
570
570
464
464
359
359
253
2
200
253
2
200
2
100
0
100
200
West
2
100
0
100
200
West
East
(km)
East
(km)
10
2
5
cm
2
3
10
2
5
cm
2
3
2050 sec
N
0
2331 sec
N
0
3
3
0.0
676
0.5
1.0
1.5
2.0
2.5
0.0
676
0.5
1.0
1.5
2.0
2.5
570
570
464
464
359
359
253
2
253
200
100
0
100
200
2
2
200
2
100
0
100
200
East
(km)
East
(km)
West
West
Figure 4.16c
Computer simulation including a background eastward neutral wind and
finite Pedersen conductivity in the off-equatorial E region. [After Zalesak et al. (1982).
Reproduced with permission of the American Geophysical Union.]
decrease. This means that the eastward plasma drift inside the plume is smaller
than the background plasma drift, and it lags behind the rest of the ionosphere.
The result is a tilt toward the west with altitude.
4.3.2 Simulations Including Seeding and Shear
Huang and Kelley (1996) have simulated the seeding effect of gravity waves on
the ionosphere with and without plasma instabilities. To accomplish this, they
included a neutral wind of the form
=
16
a
z
e
i
(
ω
t
−
k
x
x
+
k
z
z
)
m
U
a
x
+
ˆ
4
ˆ
/
s
where
B
remains in the
a
y
direction to the north. They chose
k
x
ˆ
=
(
2
π/
240
)
(rad/km) and
k
z
=
(
(rad/km), which are reasonable values for a gravity
wave perturbation. The values of wind speed and the wave vector are such that
2
π/
60
)
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