Geoscience Reference
In-Depth Information
Conjugate observation of MSTID
Jun 1, 2003 630 nm airglow
Shigaraki
13.32 UT
14.02 UT
14.32 UT
40
38
38
38
20
36
36
36
0
34
34
34
32
32
32
2
20
30
30
30
40
2
132
134
136
138
140
132
134
136
138
140
132
134
136
138
140
Long. (deg.)
Long. (deg.)
Long. (deg.)
Renner springs
13.32 UT
14.02 UT
14.32 UT
40
2
14
2
14
14
2
20
16
16
16
2
2
2
18
18
18
2
2
2
0
2
20
2
20
2
20
20
2
22
22
22
2
2
2
2
40
130
132
134
136
138
130
132
134
136
138
130
132
134
136
138
Long. (deg.)
Long. (deg.)
Long. (deg.)
Figure 6.29
Simultaneous images of MSTIDs in both hemispheres from June 1, 2003.
Note that when projected along the magnetic field, a feature in the top left-hand side
of the Shigaraki image (upper panel) maps to a feature on the bottom left-hand side of
the Renner Springs image (bottom panel). [After Otsuka et al. (2004). Reproduced with
permission of the American Geophysical Union.] See Color Plate 19.
outside the equatorial region. The plasma simply falls down the magnetic field
lines. The situation in Fig. 6.14b is unique in that it seems to describe a situation
that is not in equilibrium but remains at a high enough altitude for a long enough
time that gravitational current can drive the Rayleigh-Taylor instability.
Perkins noted, however, that an equilibrium was possible if the plasma was
supported against gravity by a southward neutral wind,
U
s
. In this case, the
condition for no vertical ion motion is:
sin
2
I
U
s
cos
I
sin
I
=
(
g
/<
v
in
>)
(6.18a)
The situation is illustrated in Fig. 6.14a. On Sept. 16-17, 1999, the post-
sunset ionosphere was held aloft stably for several hours and then fell quickly
into the atmosphere and almost disappeared. In the stable equilibrium state, if
the ionosphere is displaced upward,
decreases and gravity causes it to fall
back. If it is displaced downward, the wind (or electric field) causes it to move
back up to the equilibrium height. On other nights it seems that the effective
wind was variable, causing modulations of the equilibrium, but near midnight a
general collapse occurred.
v
in
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