Geoscience Reference
In-Depth Information
U.T.
13
17
21
01
05
09
13
08-09 Aug 1972
500
0
AU
AL
09-10 Aug 1972
AU
0
2500
AL
Jicamarca vertical drifts - Average quiet day
08-09 Aug 1972
40
3
2
2
1
2
1
5
2
7
2
8
1
7
2
0
4
1
09-10 Aug 1972
SpF
4
1
3
1
2
1
2
2
2
1
0
4
3
1
3
2
2
40
SpF
08
12
16
20
Local time (758W)
00
04
08
Figure 3.28
Auroral magnetic fields and F-region vertical drifts at Jicamarca on August
8-10, 1972. The solid curves in the lower panel show the average quiet-time diurnal
variation. Deviations from this pattern beginning at 2300 LT on August 8 are due to
direct penetration effects, whereas the slower deviations starting at 2200 LT on August 9
are due to the disturbance dynamo. [After Fejer et al. (1983). Reproduced with permission
of the American Geophysical Union.]
3.5 Feedback Between Electrodynamics and
Thermospheric Winds
We now return briefly to the problemof the large calculated thermospheric winds
mentioned in Section 3.2. Part of the key to this dilemma lies in the crucial role
of the plasma in controlling the thermospheric wind, even though the ionized
component is only a very minor constituent (one part in 10
3
at 300 km). When
a moving neutral particle strikes an ionized particle at rest in the thermosphere,
some of the momentum imparted is converted into motion of the particle about
the magnetic field and yields a net deflection in the
q
(
U
B
) direction, where
q
includes the sign of the particle charge. Thus, unlike a collision with a neutral
particle, the momentum transfer does not appear as linear momentum parallel
to
U
in the ionized gas. A similarly dense minor neutral species would, after one
or two collisions, merely accelerate to a velocity equal to the background wind
×
Search WWH ::
Custom Search