Geoscience Reference
In-Depth Information
10
5
18
3
16
14
12
10
8
6
4
2
0
200
250
300
350
400
450
500
550
600
Height (km)
Figure 5.3a
Electron density profiles calculated from (5.16) with a plasma flux of
F
=
0
10
8
cm
−
2
s
−
1
(lower curve). As can
be seen from Fig. 5.3a, upward flux results in a scale height that differs from that for
diffusive equilibrium at high altitudes. (Figure courtesy of Michael Vlasov.) See Color
Plate 8.
(upper curve) and an upward plasma flux of
F
=
3
×
z
/
2
z
)
corresponds to diffusive equilibrium because exp
. Height
profiles of the electron density calculated using (5.16) with and without flux are
shown in Fig. 5.3a.
(
−
2
)
exp
(
−
5.1.5 More General Nighttime Solutions
After sunset the molecular ions disappear almost immediately, leaving the F peak
well defined at around 300 km. Now
q
=
0 but
∂
n
/∂
t
=
0. We have
∂
n
∂
=−
β
n
+
D
a
D
n
(5.17a)
t
term does not have the same altitude dependence as the
other terms, since recombination depends upon the molecular neutral density
whereas
D
a
is determined by the atomic oxygen ion mass. That is,
Unfortunately, the
β
z
)
∝
β(
e
−
1
.
75
z
, which pertains for
M
O
+
=
and
M
n
=
N
2
. However, if we take
z
)
=
β
0
e
−
z
we can find an exact solution that is very interesting (Martyn,
1956). Consider, then, this modified differential equation,
β(
∂
n
∂
=−
β
0
e
−
z
n
D
0
e
z
+
D
n
(5.17b)
t
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