Geoscience Reference
In-Depth Information
32
Ion drifts and neutral winds
28 February 1978 0420-49 UT
698
I 205
70
8
28
48
688
36
27
N 210
I 268
N 131
I 214
45
698
28
40
67
8
30
35
25
49
AV
1
68
8
38
N 209
N 140
N 140
26
35
30
668
23
40
28
24
N 278
24
30
67
8
65
8
30
22
25
668
0420
20
Mag.
North
20
658
155
8
153
8
151
8
149
8
147
8
145
8
Figure 9.14
Ground tracks and altitudes of neutral (N) and ion clouds (I) of the various
releases during the BaTMAn experiment shown in Fig. 9.13. [After Mikkelsen et al.
(1981a). Reproduced with permission of the American Geophysical Union.]
B
2
, this relationship may be written as
σ
P
=
nm
i
ν
in
/
δ
u
/δ
t
=
(
n
ν
in
/
n
n
)(
E
/
B
)
where we have assumed that the ion mass and the neutral mass are the same.
Now, since
ν
in
is proportional to the neutral density
n
n
, the latter cancels out, and
we have the interesting result that the neutral acceleration depends only on the
plasma density
n
. Using
ν
in
=
10
−
10
n
n
(see Appendix B), we can estimate the
time for acceleration to a velocity,
5
×
t
1
/
3
=
10
10
δ
u
=
(
1
/
3
)(
E
/
B
)
,tobe
δ
/
15
n
. For
10
5
cm
−
3
, as was the case in the Alaskan experiment,
a peak density of
n
=
3
×
t
1
/
3
=
δ
2000 s, which is quite short.
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