Geoscience Reference
In-Depth Information
December 25-26, 1981
Arecibo, P.R.
400
300
200
40
December 25-26, 1981
Arecibo, P.R.
Neutral velocity
80
0
0
40
0
80
Ion velocity
10
0
5
0.0
20
00
04
08
20
00
04
08
Time (LT)
(a)
Time (LT)
(b)
Figure 5.16
(a) Height of the peak electron density (
h
max
)
, meridional plasma drift veloc-
ity components (
V
⊥
N
and
V
||
)
measured over Arecibo.
[After Behnke et al. (1985). Reproduced with permission of the American Geophysical
Union.] (b) Horizontal neutral wind and ion drift velocities (positive northward) for the
same night as the data shown in (a). [After Behnke et al. (1985). Wind data supplied by
R. Burnside. Reproduced with permission of the American Geophysical Union.]
, and peak in electron density (
n
max
)
ion velocity are compared in Fig. 5.16b. The agreement between the meridional
neutral wind
direction
and that of the corresponding horizontal ion wind is
clear. The ion velocity is much smaller, however, suggesting that there may be a
partial shorting out of the electric field in the local E region or in the conjugate
hemisphere.
Although consistent with an F-layer dynamo process, even this event raises
some interesting questions. The relatively constant large ratio between local neu-
tral wind and ion velocity implies that the electrical loading effect was larger than
suggested in Fig. 5.12 for a local E-region load. Also the loading was relatively
constant with time. This seems surprising considering the length of time involved.
However, we note that the local height-integrated conductivity, which is propor-
tional to
n
ν
in
, may have been relatively constant since the layer descended (larger
ν
in
)
at the same time as the peak density was decreasing (2100 to 0100 LT). The
density and height of the layer were subsequently relatively constant until 0330.
If the conjugate F layer had a smaller neutral wind and a relatively constant
height-integrated conductivity that was slightly higher than the local F-region
conductivity, then it would act as a load and the data could be explained.
Turning to the effects of an applied electric field, the magnetosphere
supplied such an event on October 10-11, 1980, as illustrated in Fig. 5.17a. The
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