Geoscience Reference
In-Depth Information
E
o
x
^
E
s
- l a y e r
≠
0
E
p
z
^
y
^
h
5
1 0 5 k m
B
I
≈
5 0
8
k
radar
S
N
J
H
5
H
E
o
J
P
5
P
( E
p
1
E
o
)
≈
0
≠
0
≈
0
E
p
I
x
E
o
z
^
E
s
B
0
z
^
B
5
x
^
E
o
y
^
W
E
Figure 6.39
Geometry for generating large polarization electric fields. [After Haldoupis
et al. (1996). Reproduced with permission of the American Geophysical Union.]
E layer. But if the layer is localized zonally by sharp boundaries and if no charge
leaks off to the local F region and/or the conjugate E and F regions, a large east-
ward polarization field will build up to keep
0. Using their geometry and
notation, the eastward polarization field is denoted by
E
x
and we have,
E
x
=
σ
H
∇
·
J
=
E
y
−
E
x
(6.28)
σ
P
where
E
x
is the eastward component and
E
y
is the southward component of
the dynamo electric field. Since
σ
H
/σ
P
can easily exceed a factor of 10, the
polarization field can drive the two-stream instability. Similarly, a zonal wind (
u
e
)
will polarize a zonally localized patch with an electric field of value
u
e
B
,
which then drives a meridional current that can be quite large. But in either case,
one might wonder, why doesn't the thin sporadic E layer polarize and stop the
current? In fact, it does polarize but only in such a way as to stop the vertical
component of the current. This is easy to do since the conductivity along
B
is
very large.
(σ
H
/σ
P
)
Search WWH ::
Custom Search