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12
Auroral
808
18
6
Trou
gh
0
MLT
Figure 9.9
The plasma stagnation that may produce the depletions seen in Fig. 9.8 occur
when the magnetospheric convection pattern and the corotation velocity are combined,
as shown here. [After Brinton et al. (1978). Reproduced with permission of the American
Geophysical Union.]
J
P
=
σ
P
E
. When all of these effects are considered, the ion temperature can be
expressed as (St.-Maurice and Hanson, 1982):
2
T
i
=
T
eq
+
(
m
n
φ
in
/
3
k
B
ϕ
in
)
|
V
i
−
V
n
|
(9.11)
where
T
eq
=
T
n
+
[
(
m
i
+
m
n
)ν
ie
/
m
i
ν
in
ϕ
in
]
(
T
e
−
T
i
).
(9.12)
Here the dimensionless parameters
ϕ
in
depend on the nature of the colli-
sional interactions between the ions and the neutral gas, but above about 200 km,
where O
+
collides principally with atomic oxygen, both of these parameters are
approximately unity.
These expressions show that the ion temperature will increase from its equilib-
rium value whenever a relative velocity exists between the ion and neutral gases.
This relationship between the ion drift velocity and the ion temperature can eas-
ily be seen at high latitudes, where the magnetospheric electric field can rapidly
produce ion velocities that greatly exceed the neutral gas velocity. One such
example is shown in Fig. 9.10, where an extremely good correlation between
φ
in
and
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