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Jicamarca
80
800
SpF
H
MP
23 September 1987
40
600
0
400
2
40
200
80
800
24 September 1987
40
600
0
400
2
40
200
80
800
25 September 1987
40
600
0
400
240
200
16
18
20
Local time
22
24
Figure 4.10
Vertical drift velocities (circles), heights of maximum backscattered power
(
x
, and spread F scattering layers (vertical lines) during March 1985. The maximum
height probed by the radar was 650 km. [After Fejer et al. (1999). Reproduced with
permission of the American Geophysical Union.]
)
4.2.2 The Generalized Rayleigh-Taylor Process: Electric Fields,
Neutral Winds, and Horizontal Gradients
Gravity is not the only destabilizing influence in the equatorial ionosphere. If
we return to (4.5), we can include the effect of the ambient electric field
E
0
as
well as the neutral wind. The latter can easily be included by remembering (see
Chapter 3) that when electric fields and winds both exist, the current density
is
E
0
where
E
0
σ
·
=
E
0
+
U
×
B
. Since the fundamental destabilizing source
σ
P
E
is the correct quantity to investigate. First we note that for
a zonally eastward electric field, the zero-order Pedersen current is in the same
direction (
g
is the current,
B
) as the gravity-driven current. The derivation outlined previ-
ously, which considered only gravity, can be generalized to include the effect
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