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Vertical drift velocities
33.027 - Punta Lobos, Peru
Upleg
Downleg
120
2C
s
(11
)
C
s
(1
1
)
2C
s
(11
)
C
s
(1
1
)
115
110
105
100
95
90
85
21000
2500
0
500
1000
21000
2500
0
500
1000
Velocity (m/s)
Velocity (m/s)
Figure 4.35a
Vertical drift velocities associated with the horizontal electric fields mea-
sured during the upleg and downleg traversals of the electrojet by rocket 33.027.
The boundaries corresponding to
C
s
(
, which represent the two-stream instabil-
ity threshold, are also shown for a fixed value of
T
e
. The figure demonstrates why vertical
two-streamwaves were only detected in the narrow region of roughly 100-107 km for this
day. [After Pfaff et al. (1987b). Reproduced with permission of the American Geophysical
Union.]
1
+
)
The necessary condition for the generation of vertically propagating type 1 irreg-
ularities is given by the requirement (see Section 4.6) that
(δ
E
/
B
)>(
1
+
)
C
s
(4.53)
which corresponds to the dotted lines in Fig. 4.35a. Using (4.44) this can also be
written
V
D
/(
2
A
(ν
i
/
i
)
1
+
)
>
C
s
(4.54)
where again we have used
A
to represent the amplitude of the
variation
as defined above. Neglecting ion inertia, secondary gradient drift irregularities
are generated if
(δ
n
/
n
)
ν
i
V
D
k
p
2
m
2
A
2
M
k
s
C
s
/ν
i
ν
e
(
+
)
1
>
(4.55)
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